SLOVAK AGRICULTURAL UNIVERSITY
FACULTY OF AGROBIOLOGY AND FOOD RESOURCES
Dean: Prof. Ing. Daniel Bíro, PhD.
DEPARTMENT OF PLANT PROTECTION
Head of department: Prof. Ing. Ľudovít Cagáň, CSc.
European corn borer populations and their natural enemies in
central Europe
Supervisor:
Prof. Ing. Ľ. Cagáň, CSc
Ing. Anna Plačková
CONTENT
1. INTRODUCTION
2. LITERATURE REVIEW
2.1. Description of Ostrinia nubilalis
2.2. Ostrinia nubilalis characteristic
2.2.1. Bacteria and fungies assosiated with Ostrinia nubilalis
2.2.2. Influence of environmental conditions on Ostrinia nubilalis
2.2.3. Overwintering and diapause of Ostrinia nubilalis larvae
2.2.4. Influence of adult feeding on Ostrinia nubilalis satges
2.2.5. Role of sex pheromones and population structure
2.2.6. Choise of oviposition site
2.2.7. Damage of maize caused by Ostrinia nubilalis
2.3. Ostrinia nubilalis in Slovakia
2.4. Occurrence of Ostrinia nubilalis in Europe and USA
2.5. The sources of control
2.5.1. Agrotechnics
2.5.2. Possibilities of chemical control and biological solutions (treatment)
2.5.3. Sources of control with “Bt corn”
2.5.3.1.
Correlation between Bt corn and natural parasitoids of Ostrinia
nubilalis
2.5.4. Mechanisms of natural control and new technics
2.5.4.1.
Influence of vegetation and natural conditions on the parasitoids
of Ostrinia nubilalis
2.5.4.2.
Use of modern technologies and biological control
2.5.4.3.
Role of order Hymenoptera
2.5.4.4.
Natural predators of Ostrinia nubilalis
2.6. Parasitoids of Ostrinia nubilalis and their bionomy
2.6.1. Lydella thompsoni Herting
2.6.2. Sinophorus turionus Ratz
2.6.3. Eriborus terebrans Gravenhorst
2.6.4. Microgaster tibialis Nees
2.6.5. Macrocentrus grandii Goidanich
2.6.6. Bracon hebetor Say
2.6.7. Sympiesis viridula Thompson
2.7. Characteristic of microsporidia
2.7.1. Effect of environmental factors
2.7.1.1.
Solar radiation/ sunlight
2.7.1.2.
Temperature
2.7.1.3.
Moisture/ humidity
2.7.1.4.
Effect of pH
2.7.1.5.
Wind
2.7.1.6.
Interactions between above factors
2.7.1.7.
Substrate effects
2.7.1.8.
Food
2.7.1.9.
Insect cadavers
2.7.1.10.
Infected living host
2.7.1.11.
Insecticides/ adjuvans
2.8. Nosema pyrausta Pailot
2.8.1. Infection and the way of spread of Nosema pyrausta spores
2
2.8.2. Influence of Nosema pyrausta spores on the life stages of Ostrinia
nubilalis
2.8.3. Influence of Nosema pyrausta on the food consumption
2.8.4. Nosema pyrausta and Bt maize
2.8.5. Influence of Nosema pyrausta on the parasitoids of Ostrinia nubilalis
2.9. Ostrinia nubilalis and host plants
2.9.1. Natural plant resistance
2.9.2. Plant base odors influencing Ostrinia nibilalis
2.9.3. Plant odors influencing parasitoids of Ostrinia nubilalis
2.9.4. Weed abundance influencing Ostrinia nubilalis infestations
3. GOALS
3.1. To characterize Ostrinia nubilalis population and infestation in Slovakia
3.2. To characterize species spectrum of the Ostrinia nubilalis parasitoids
3.3. To get information about microsporidian infection in north-west part of
Slovakia and south part of Czech Republic
3.4. To check the influence of microsporidian infection caused by Nosema pyrausta
from Slovakia on populations of Ostrinia nubilalis from various countries
4. MATERIAL AND METHODS
5. RESULTS
6. DISCUSSION
7. SUMMARY
8. CONTRIBUTION OF THE WORK FOR PRACTICAL USE AND SCIENCE
9. REFERENCES
10. APPENDIX
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1. INTRODUCTION
Practical plant protection is not possible without very intensively study of bionomy,
noxiousness, environmentalism and methods of control. This study is possible only, when the
observation is oriented to the pest in special ecological conditions. The European corn borer
(ECB), Ostrinia nubilalis (Hübner), is the most important maize pest in Slovakia and is
responsible for considerable yield loss each year (Cagáň, Grenčík, 1990). O. nubilalis is
originated in Europe, where it is widespread. It also occurs in northern Africa. North
American O. nubilalis population is thought to have resulted from multiple introductions from
more than one area of Europe. Thus, there are at least two, and possibly more, strains present
(Capinera, 2000). O. nubilalis is known to be polyphagous species. It is known to attack over
200 plants (Lewis, 1975), but maize is a preferred host. O. nubilalis has achieved pest status
in crops like potato (Kennedy, Anderson, 1981) and cotton (Gossipium hirsutum L.) (Savinelli
et al., 1986). Occasionally it causes economic damage in diverse other crops such as apple
(Pyrus malus L.), onion (Allium cepa L.), soybean, snap bean and pepper (Shower et al.,
1989, cit. Capinera, 2000). At the moment, new possibilities how to reduce O. nubilalis are
looked out. Goidanich (1931) mentioned more than 1000 species of enemies of O. nubilalis,
out of these 78 are parasitoids (Goidanich, 1931).
2. LITERATURE REVIEW
2.1. Description of Ostrinia nubilalis
There are 20 species within the genus Ostrinia, four of which are recognized as a pests:
Ostrinia nubilalis, O. furnacalis, O. obumbratalis, O. zaguliaevi. The European corn borer,
Ostrinia nubilalis (Hübner), is also known under the synonyms : Pyralis nubilalis Hübner,
Micractic nubilalis Hübner. This insect species that belongs to the:
Superkingdom: Eukaryota
Kingdom: Animalia
Subkingdom: Metazoa
Phylum: Arthropoda
Subphylum: Hexapoda
Superclass: Hexapoda
Class: Insecta
Subclass: Pterygota
Superorder: Endopterygota
Order: Lepidoptera
Suborder: Glossata
Superfamily: Pyraloidea
Family: Crambidae
Subfamily: Pyraustinae
Genus: Ostrinia
(Merops, 2005)
Adult - The moths are fairly small, with males measuring 20 to 26 mm in wingspan, and
females 25 to 34 mm. It is colored pale yellow to light brown. The outher third of the wings is
usually crossed by dark zigzag lines. The male moth is smaller, more slender, and darker than
the female. The outer third of its wings is usually crossed by two zigzag streaks of pale
4
yellow, and often there are pale yellow areas on the forewings. The sex pheromone has been
identified as 11-tetradecenyl acetate, but eastern and western strains differ in production of Z
and E isomers. The preoviposition period averages about 3.5 days. Duration of oviposition is
about 14 days, with oviposition averaging 20 to 50 eggs per day. The female often deposits
400 to 600 eggs during her life span. Total adult longevity is normally 18 to 24 days
(Capinera, 2000; Carter, 1984).
Egg - Eggs are deposited in irregular clusters of about 15 to 20 on the underside of leaves, and
overlap like shingles on a roof or fish scales and are covered with a shining waxy substance.
Eggs measure about 1.0 mm in length and 0.75 mm in width. Each white egg is about half the
size of a pinhead. The eggs change to pale yellow and darken just before hatching as the
brown head of the borer inside becomes visible. Eggs hatch in four to nine days (Capinera,
2000; Carter, 1984).
Larva - The newly hatched larva, about 1.5 mm long, has a black head, five pairs of prolegs,
and a pale yellow body bearing several rows of small black or brown spots. It develops
through 5 or 6 instars to become a fully grown larva about 25 mm long (Capinera, 2000;
Carter, 1984; Hagerman, 1997). Head capsule widths are about 0.30, 0.46, 0.68, 1.03, 1.66,
and 2.19 mm in instars 1 through 6, respectively. Mean body lengths during the six instars are
about 1.6, 2.6, 4.7, 12.5, 14.5, and 19.9 mm, respectively. Young larvae tend to feed initially
within the whorl, especially on the tassel. When the tassel emerges from the whorl, larvae
disperse downward where they burrow into the stalk and the ear. Mortality tends to be high
during the first few days of life, but once larvae establish a feeding site within the plant
survival rates improve (Capinera, 2000; Carter, 1984). After fifth instar, the first generation of
the bivoltine strain turns to a pupa inside the stalk, tassel, etc. and emerges a few weeks later
as an adult to begin the second generation. Corn borers that reach fifth instar in the fall enter
an inactive phase called diapause, in which they spend the winter. They will not pupate until
spring (Hagerman, 1997). Larvae in the final instar overwinter within a tunnel in the stalk of
corn, or in the stem of another suitable host. Duration of the instars varies with temperature.
The developmental treshold for the larvae is about 11 °C. Under field conditions development
time was estimated at 9.0, 7.8, 6.0, 8.8, 8.5, and 12.3 days for instars 1 through 6,
respectively, for a mean total development period of about 50 days, but this varies
considerable from year to year according to weather conditions. (Capinera, 2000; Carter,
1984).
Pupa - Pupae usually occur in April or May, and then later in the year if more than one
generation occurs.The brown pupa is 13 to 15 mm long with a smooth capsule-like body.
Pupae usually occur in April or May, and normally is yellowish brown color. The pupa
measures 13 to 14 mm in length and 2 to 2.5 mm in width in males and 16 to 17 mm in length
and 3.5 to 4 mm in width in females. The pupa is ordinarily, but not always, enveloped in a
thin cocoon formed within the larval tunnel. Duration of the pupal stage under field conditions
is ussually about 12 days. The developmental treshold for the pupae is about 13 °C (Capinera,
2000; Carter, 1984).
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2.2. Ostrinia nubilalis characteristic
2.2.1. Bacteria and fungies assosiated with Ostrinia nubilalis
Lynch et al., (1975) isolated bacteria from egg masses of O. nubilalis which were identified
by biochemical and other definitive tests as: Bacillus thuringiensis var. kurstaki, B. cereus, B.
megaterium, Acinetobacter spp., Erwinia herbicola, Enterobacter cloacae, Serratia
marcescens, Pseudomonas spp., and Xanthomonas sp. With the exception of S. marcescens
and Pseudomonas spp., this is the first report of these bacteria from insect eggs. In addition,
Enterobacter sp., Klebsiella sp., Micrococcus luteus, Streptococcus sp. and S. faecalis were
isolated from first-instar larvae. Lynch and Lewis (1977) in their later tests with egg masses
isolated fungies from field-collected egg masses of O. nubilalis, which were identified as
Alternaria spp., A. porri, Fusarium spp., Fusarium oxysporum, Beauveria bassiana, Mucor
spp., and an unidentified yeast. Most fungi were associated with predator injury to the egg
mass. Bioassay of fungi on egg masses, however, showed that Alternaria spp. and A. porri
reduced the hatch of both injured and uninjured egg masses, and Mucor sp. reduced the hatch
only when the egg mass was injured (Lynch, Lewis, 1977). Bruck and Lewis (1999) sampled
natural enemies of O. nubilalis along field borders with differing vegetation levels. Maize
fields adjacent to three broad classes of border vegetation: herbaceous, intermediate, and
wooded. Collected larvae were evaluated for presence of the entomopathogens Beauveria
bassiana (Balsamo) Vuillemin (Deuteromycotina: Hyphomycetes) (Bruck, Lewis, 1999).
Fungies of the genus Fusarium, are common fungal contaminants of maize and are also
known to produce mycotoxins. Maize that has been genetically modified to express a Bt
endotoxin has been used by Bakan et al., (2002) to study the effect of insect resistance on
fungal infection of maize grains by Fusarium species and their related mycotoxins. Maize
grain from Bt hybrids and near-isogenic traditional hybrids was collected in France and Spain
from the 1999 crop, which was grown under natural conditions. According to the ergosterol
level, the fungal biomass formed on Bt maize grain was 4-18 times lower than that on
isogenic maize. Fumonisin B, grain concentrations ranged from 0.05 to 0.3 ppm for Bt maize
and from 0.4 to 9 ppm for isogenic maize. Moderate to low concentrations of trichothecenes
and zearalenone were measured on transgenic as well as on non-transgenic maize.
Nevertheless, significant differences were obtained in certain regions. The protection of maize
plants against insect damage (O. nubilalis and Pink stem borer) through the use of Bt
technology seems to be a way to reduce the contamination of maize by Fusarium species and
the resultant fumonisins in maize grain grown in France and Spain (Bakan et al., 2002). O.
nubilalis is a major pest of maize in Central Europe and is suspected to promote infection of
maize with Fusarium species. Magg et al., (2003) in their study determined moniliformin
(MON) concentration in early maturing European Bt maize hybrids, their isogenic
counterparts, commercial cultivars and experimental hybrids. Also evaluated the association
between MON concentration and O. nubilalis resistance and correlated MON concentration
with concentrations of other mycotoxins determined from the same plant materials. The field
experiments were performed at five locations in Germany. MON concentration was
significantly higher with manual infestation of O. nubilalis larvae (296 mug/kg) than under
insecticide protection (66 mug/kg). Bt hybrids showed significantly lower MON
concentrations and higher grain yields under manual O. nubilalis infestation than their
corresponding isogenic counterparts, as well as commercial and experimental hybrids. All
ECB resistance traits and grain yield under O. nubilalis infestation were significantly
correlated with MON concentration. Correlations between concentrations of MON and other
Fusarium mycotoxins were not significant. The use of Bt maize hybrids or insecticides to
control O. nubilalis reduces the contamination of maize grains with MON in Central Europe.
6
The presence of resistance genes against Fusarium species in the current elite maize
germplasm was indicated by O. nubilalis susceptible non-Bt hybrids with low-MON
concentrations (Magg et al., 2003). Fusarium ear rot of corn is associated with feeding
damage from the ECB and the corn earworm (CEW), Helicoverpa zea Boddie. Specific
transformation events encoding for Cry1Ab protein from Bt corn may reduce Fusarium ear rot
and fumonisin concentration in grain by minimizing damage from certain insects. The
objective of this study was to determine if effects from Cry1Ab protein in kernels and silks on
fumonisin concentration in grain vary depending on the genotype of the hybrid or the
predominant insect species. Four Bt corn hybrids and their corresponding nontransgenic, nearisogenic hybrids were compared for ear rot severity and fumonisin concentration in grain in
four environments. Treatments included inoculation with F. verticillioides (Sacc.) Nirenb.
(Syn=F. moniliforme J. Sheld.) and F. proliferatum (Matsushima) Nirenb., infestation with
ECB larvae, infestation with CEW larvae, and controls. Cry1Ab protein from the Mon810
transformation event was associated with reduced ear rot severity when hybrids were not
inoculated with Fusarium spp., regardless of whether hybrids were infested or not infested
with insects. Cry1Ab protein was associated with reduced fumonisin concentration in grain
when ECB was the predominant insect, but not when CEW was the predominant insect.
Cry1Ab protein was not associated with reduced fumonisin concentration in grain for the
most resistant hybrid pair in this study. Results suggest that Bt hybrids can reduce fumonisin
concentration in grain during seasons when ECB is favored, but not during seasons when
CEW is favored. Hybrid genotype was an important factor in reducing fumonisin
concentration in grain (Clements et al., 2003). Stalk and ear rots caused by Fusarium
subspecies are often related to mycotoxin accumulation in maize kernels. Various
mycotoxicoses in livestock and humans are triggered by the consumption of these toxins. O.
nubilalis reportedly promotes the infection by Fusarium spp. Papst et al., (2005) in their study
evaluated the concentration of deoxinivalenol (DON), 3-acetyl-deoxynivalenol (3-A-DON),
15-acetyl-deoxynivalenol (15-A-DON), fumonisin (FUM), fusarenon-X (FUS-X),
moniliformin (MON), and nivalenol (NIV) in kernels; and determined the level of O.
nubilalis resistance and investigated the association between the concentration of mycotoxins
and O. nubilalis resistance. Their study used early maturing European Bt (Bacillus
thuringiensis) cultivars, their isogenic counterparts, and commercial hybrids. The field
experiments were conducted at three locations in Germany. The mycotoxins most prevalent
were DON, FUM, and MON. Plots infested by and protected from O. nubilalis differed
significantly for DON and FUM concentrations. In addition, significant differences were
found for concentrations of FUM between isogenic Bt and non-Bt hybrids. The two Bt events
- Bt176 and Mon810 - were also significantly different for FUM concentrations. Not all
mycotoxins were related to O. nubilalis damage. According their results the insect
management and, therefore, the use of Bt cultivars may be a short-term solution to minimize
toxins in kernels (Papst, 2005). Alma et al., (2005) studied the relationships between the
feeding activity of O. nubilalis and mycotoxin contamination of kernels in Italian maize crop
systems. At harvest, kernel contamination by fumonisins and zearalenon was measured and
related to the number and position of tunnels on maize ears. The number of maize plants
injured from second-generation larvae was partially reduced by using deltamethrin (-35%)
and by bringing forward planting (-12%), whereas differences in nitrogen and water supply
had little effect. The abundance of the first generation was, on average, low. The amount of
fumonisin was generally one scale point higher in injured ears, and was positively related to
ear tunnelling: tunnels in the apex seemed to increase the amount of contamination. No links
were detected between O. nubilalis presence and zearalenon contamination (Alma et al.,
2005). Ozakova et al., (2006) conducted field trials in southern Russia during 2001-02 to
study the effect of biological control agents, including Flavobacterin [Pseudomonas
7
fluorescens], Agrophyl, Mizorin, and strains 8, 076, 137G and 880 on plant and disease
control. The results of investigations revealed occurrence of flea beetles, leafhoppers, aphids,
corn earworm H. armigera and corn borer O. nubilalis. Smut fungi, Helminthosporium,
bacterial spot disease and Fusarium of cobs were the main diseases, followed by white rot of
stems and bacterial disease of cobs. Popov et al., (2006) in his field study also confirmed that
O. nubilalis and D. virgifera are the most harmfull pests in maize which are associated with
Pythium spp. and Fusarium spp. Slezakova et al., (2006) studied in 2002-2004, the efficacy of
Bt maize for controlling the O. nubilalis and grain infection by toxigenic micromycetes in
Bohemia (Praha-Ruzyň) and Moravia (Ivanovice na Hané), Czech Republic, and compared
with that of biological control by a Trichogramma wasp. Injury on plants caused by ECB
differed according to the locality. In Ivanovice na Hané, the occurrence of pest and toxigenic
micromycetes species was greater. Bt maize showed a high level of resistance to ECB, thus,
no injured plants was observed. In grain samples, a total of 15 taxa of the genus Fusarium and
9 taxa of the genus Penicillium were identified. A similar complex of micromycetes was
recorded on Bt maize and the non-transgenic hybrids. However, the frequency of Fusarium
species was significantly lower in Bt maize than in the non-transgenic hybrids. In Bt maize,
the reduction in frequency reached 35.3% for Fusarium oxysporum, 100.0% for F.
proliferatum, 61.6% for F. sporotrichioides, 32.4% for F. subglutinans [Gibberella fujikuroi
var. subglutinans], and 77. 6% for F. verticillioides [Gibberella moniliformis]. Bt maize was
infected by toxigenic micromycetes at a lower level compared to non-transgenic hybrids, and
its grains had lower amounts of fumonisins, deoxynivalenol and zearalenol (Slezakova et al.,
2006). Sass et al., (2007) also has confirmed that O. nubilalis is one of the most important
pests of maize. Injuries to the plants caused by the larvae of the ECB may represent entrance
gates for fungal-spores. In the conventional variety on both of the experimental fields was
found a high Fusarium spp. infestation (70%). Especially species of the section Liseola
dominates, among them: F. subglutinans, F. proliferatum und F. verticillioides (Saas et al.,
2007). The most common Fusarium diseases of maize, causing cob, root and stem rots, are F.
graminearum [Gibberella zeae], F. verticillioides [G. moniliformis], F. proliferatum and F.
subglutinans [G. fujikuroi var. subglutinans]. Infection processes, O. nubilalis as a vector and
mycotoxin production are discussed. Growing resistant hybrids as a means of disease
prevention, and chemical and cultural control methods are considered (Ivic, Cvjetkovic,
2007). O. nubilalis is the main maize pest in Central and South Europe and it promotes the
infection of maize with Fusarium verticillioides, which produces fumonisins. (Saladiny et al.,
2008; Blandino et al., 2008) in his study determined the effect of time of application of
insecticide treatments on ECB damage, F. verticillioides [Gibberella moniliformis] infection
and fumonisin contamination. The field experiments were performed from 2006 to 2007 in 2
locations in North West Italy. Seven times of insecticide application were compared, from
maize flowering to approximately 15 days after the ECB flight peak. At harvest, ears were
rated for the incidence and severity of ECB damage and Fusarium ear rot symptoms;
moreover, the harvested kernels were analysed for fumonisins B1 + B2 ( (b) Blandino et al.,
2008). Fusarium verticillioides, a known producer of fumonisins, has been reported to be the
most common pathogen of maize causing Fusarium ear rot and grain fumonisin
contamination. Field tests were carried out in 2004 and 2005 growing seasons in two sites
located in the North of Italy to determine the effects of sowing date and insecticide treatment
against ECB on maize susceptibility to Fusarium ear rot and fumonisin contamination under
natural infection conditions ((a) Blandino et al., 2008). Mycotoxins are the result of the
penetration of maize cobs by the pyralid O. nubilalis; this allows fungi such as Aspergillus
spp., Fusarium spp. and Penicillium spp. to develop on the cob and metabolize, producing
aflatoxin, fumonisine and ocratoxin respectively (Mingardo, 2008).
8
2.2.2. Influence of environmental conditions on Ostrinia nubilalis
Young larvae are extremely sensitive. Those which fall to the ground or into a drop of water,
or emerge at a point of the plant where food material is not sufficiently tender or is in the
other ways unsuitable, propably die very rapidly. A slight injury of any kind or a short
deprivation of proper food is sufficient to cause a very high mortality among the young larvae
(Anonymous, 1928). Most caterpillars do not survive more than a few days, but succumb to
desiccation, predatory insects, drowning in rainwater. There are many reports that weather
influences O. nubilalis survival. Heavy precipitation during egg hatch, for example, is
sometimes given as an important mortality factor. Low humidity, low nighttime temperatures,
and heavy rain and wind are detrimental to moth survival and oviposition. However, during a
10-year, 3-state study, (Sparks et al.,1967) reported no consistent relationship between
weather and survival. According to Showers et al., (1976, 1980) environmental conditions can
have a major impact on the size of insect population. O. nubilalis adults aggregate in dense
vegetation at the edge of maize fields (action sites) to mate and rest. Under favorable
conditions females leave the action sites at the night to oviposit in nearby maize fields. Under
unfavorable conditions for oviposition – cool, wet weather, moths remain in the action sites
and do not oviposit (Showers et al., 1976, 1980). The results are reported of field studies in
1975-78, by means of light-traps in maize fields in the Bergamo area of Italy, on the adult
emergence of O. nubilalis, especially as affected by temperature; these indicated a close
relationship between the cumulative frequency of emergence and the cumulative number of
thermal units, which confirmed the paramount importance of temperature in controlling the
life-cycle of the insect. The regression equations relating to the mean frequencies of moth
flights and the accumulation of thermal units were calculated for the first and second
generations, and made possible the forecasting of the number of thermal units required to
obtain given emergence frequencies (Coppolini, 1979). During outdoor tests in Romania of
different varieties of maize for their relative susceptibility to O. nubilalis environmental
factors influencing the population level of the pest were noted. Unfavourable weather
conditions such as heavy showers, rain and hail together, storms, or temperatures of over 32
deg C for several days on end reduced Ostrinia populations drastically if they occurred during
the hatching period or the first larval instar. Other environmental factors adversely affecting
populations of O. nubilalis were parasites (such as Lydella thompsoni Herting (senilis auct.)
and Bracon brevicornis Wesm. (Microbracon brevicornis)), pathogens (such as Beauveria
bassiana) and predatory birds near woods (especially woodpeckers), besides plant resistance
to pest attack (Barbulescu, 1984). Hagerman (1997) confirmed in his tests in Ontario, that the
weather conditions that occur while female corn borers are laying eggs are probably the
greatest factor in determining the size of the population in a given year. For most of Ontario,
peak egg laying occurs in a two-week period, usually in late July. In the bivoltine area there
are two peaks usually in late June and again in late August. Warm calm nights with dew will
maximize egg laying and increase the risk of damage in the field. Over-wintering weather also
influences corn borer survival to a small extent. The diapausing larvae are able to survive very
cold temperatures but mortality is increased by freeze and thaw cycles. Many borers are also
killed over the winter by insect-eating mammals and birds (Hagerman, 1997). Keszthelyi and
Lengyel (2003) has also confirmed that the meteorological elements (temperature,
precipitation and relative humidity) significantly influenced the possibility of trapping in the
case of both sexes. The female sex ratio had close correlations with the minimum, maximum
and average temperature and precipitation data (Keszthelyi Lengyel, 2003). Trnka et al.,
(2007) in their study used the multi-generational phenology model ECAMON. The model
enabled to predict the development of the ECB, to estimate the risk of its establishing a
permanent population, and to give an indication of climate-related stress factors affecting the
9
species. The evaluation of ECAMON demonstrated that it provides accurate predictions of the
onset and duration of the key phenological stages over a broad range of sites. It explains over
70% of the variation in the timing of key developmental stages based only on daily weather
data. ECAMON simulations correctly predicted the presence/absence of the ECB over the
study region during the 1961-1990 reference period. It also helped to explain the sudden
increase in the maize infestation over the territory of the Czech Republic during the unusually
warm period of 1991-2000. The ECAMON results demonstrated that the effect of climate will
be significant and complex (Trnka et al., 2007). Three years (2000-2002) of field studies were
conducted in mid-Missouri, USA, to assess the impact of various compositions of herbaceous
field borders on populations of the O. nubilalis. Border treatments of: (1) a mixture of warmseason grasses and legumes, (2) a mixture of cool-season grasses and legumes, (3) tall fescue
alone, and (4) a corn border control were planted around plots of field corn. Percent stalks
infested with European corn borer and number and length of larval tunnels in stalks were
analysed. Warm-season vegetation-bordered corn had consistently lower percent stalks
infested than corn bordered by cool-season vegetation, tall fescue or a corn control (Stamps et
al., 2007). The small-scale dispersal of the ECB was studied in a release-recapture experiment
using reared dye-marked adults. Thereby, six light trap cages were set up across two maize
fields at 50-m intervals. In total, 736 marked ECBs were released, of which 10.2% were
recaptured together with 212 unmarked naturally occurring adults after a period of 48 h. All
marked-released individuals left the release point, with a mean dispersal distance of 195 m.
Eighty-two per cent of the recaptured ECBs moved to the second maize field across a ditch
and associated shrubs. The spatial and temporal patterns of incidence of naturally occurring
ECBs in the traps were consistent with those of the marked moths and showed an
inhomogeneous distribution. There was a highly significant relationship between male and
female densities in the cages. No ECBs were caught during a period of adverse weather
conditions. Dispersal distances may be influenced by plant size, weather conditions during the
flight, pheromonal patterns in the field and the timing of the flight (Engels et al., 2008).
2.2.3. Overwintering and diapause of Ostrinia nubilalis larvae
Mature larvae in fifth instar overwinter inside tunnels in stubble, stalks, ears, or other
protective plant material. Ben-Yakir et al., (1999) compared development of O. nubilalis
under five types of covers (treatments): exposed, pea, sunflower, 30% shade and 60% shade.
In the exposed plots O. nubilalis developed the fastest but 60-90% died before emergence.
Under sparse vegetation (sunflower) or 30% shade O. nubilalis emergence took 1-2 weeks
longer and about 50% emerged. Under thick vegetation (peas as green manure) or 60% shade
O. nubilalis emergence was delayed 2-4 weeks and over 70% emerged. Thus, the density of
ground cover was inversely correlated with developmental time and directly correlated
overwintering success. Hot spells had a major role in reducing the overwintering success.
Leaving late season maize fields exposed (without crops and with herbicides treatment) until
May is expected to significantly lower the size of the O. nubilalis population that will
overwinter successfully (Ben-Yakir et al., 1999). During overwintering the larvae accumulate
glycerol and become cold resistant. In the spring the level of glycerol in the larvae decreases
(Barnes, Hodson, 1956; Gadenne et al., 1987). Many insects in temperate regions overwinter
in diapause, during which they are cold hardy. In these insects, one of the metabolic
adaptations to the unfavorable environmental conditions is the synthesis of cryoprotectants/
anhydroprotectants (Stanic et al., 1986). Overwintering larvae of O. nubilalis from different
parts of France and 1 locality in Spain were kept in the laboratory at Bordeaux, France, at 8
deg C until the termination of diapause and thereafter at 22-24 deg C and 70-80% RH, with a
photophase of 16 h. Their offspring were reared after hatching either at 27-29 or 22-24 deg C,
10
with about 75% RH and 16 h photophase. Several types of population could be distinguished
according to the incidence of larval diapause. These were polyvoltine populations from
southern or central regions with a low incidence of diapause that varied according to
geographic latitude, a northern population that had only 1 generation a year, and an aberrant
population from Lenesville in central France which, although geographically near at least one
of the populations from the south-central regions, had no diapause under either temperature
regime (Robin, 1982). Cold stress rather than diapause is though to responsible for the
glycerol acumulation (Nordin et al., 1984). Higher activity of antioxidative enzymes at the
beginning of the diapause period (November), compared to late diapause (February), showed
that glutathione and ascorbate were higher in February. Similarly a lower activity of the
hexose monophosphate shunt enzymes in February. Exposure of larvae to –12 °C resulted in
an elevation of hexose monophosphate shunt enzyme activity, especially in November. This
significant increase in glycerol content in February. Changes in ascorbate levels and
dehydroascorbate suggest a connection between the antioxidative system, metabolism during
diapause and cold hardiness. Antioxidative defense in larvae of O. nubilalis is closely
connected with metabolic changes characteristic of diapause, mechanisms of cold hardiness
involved in diapause and the maintenance of a stable redox state (Stanic et al., 1986). During
postdiapause development larvae in plant debris may be completely exposed or under various
types of vegetation. These differences in ground cover create various climatic conditions for
the developing larvae (Ben – Yakir et al., 1999). Diapause of the O. nubilalis larvae starts
very early in the summer when mean photophases are longer than 15 hours/day (Ellsworth et
al., 1989). Brains from non-diapause-bound, diapause-bound and diapausing O. nubilalis
contain prothoracicotropic hormone (PTTH) which stimulates the prothoracic glands of larvae
to produce ecdysone and 3-dehydroecdysone in a dose-dependent manner. At a dose of 0.75
brain equivalents, PTTH activity is highest in non-diapause-bound and diapausing prepupae.
Levels are approx. 50% as high in younger 5th instars. In diapausing prepupae, PTTH activity
again falls to approx. 50% after 5–8 weeks of refrigeration. Prothoracic glands from
diapausing O. nubilalis prepupae were refractory to stimulation. In vivo experiments indicate
that brains from diapausing prepupae have more moult-stimulating activity than those from
non-diapause-bound prepupae (Gelman et al., 1992). Diapause of O. nubilalis larvae is
influencing with many factrors. Ammonium ions, administered by injection of ammonium
acetate at a rate of 500 μg/borer, greatly accelerated the completion of diapause in the O.
nubilalis. The biochemical mode of action of ammonium has not been determined, but the
ions apparently exerted specific stimulation of some developmental process that is normally
regulated via the insect's temporal-photoperiodic responses. Diapausing borers tended to be
relatively refractory to ecdysone, but displayed a pathological apolysis in response to high
hormone levels under some conditions, including (1) injection of ammonium acetate, (2)
injection of sodium chloride, (3) during recovery from severe wounds, and (4) during
restoration of water balance following water deprivation. These factors influencing the borer’s
response to ecdysone were interpreted as being associated with physiological stress or injury
metabolism, because of their non-specificity. Only ammonium acetate had the effect of
accelerating the termination of diapause, and in this regard the developmental stimulation was
highly specific (Beck et al., 1969). Beck also (1987) in his later study made of another factors
determining the intensity of larval diapause in O. nubilalis. Intensity was measured in terms
of the number of days of long-day exposure (8 h dark–16 h light) at 30 °C required to evoke a
50% incidence of pupation (Days to P50) in the experimental cultures. Intensity of diapause
was found to be regulated by the duration of the scotophase and the temperature of the diel
rearing regime. Rearing temperatures of 25 and 22 °C evoked more intense diapause than did
19 °C. Within the diel range of scotophase durations, 12 h evoked greater intensity of
diapause than did either longer or shorter scotophases. Circadian resonance in the effect of
11
scotophase duration on intensity of diapause was observed at both 22 and 19 °C.
Intensification of diapause was demonstrated to occur with a rearing temperature of 19 °C,
but not at higher temperatures (22 and 25 °C). Experimental conditions that intensified
diapause (increased Days to P50) did not increase the percentage incidence of diapause. No
correlation was detected between incidence and intensity of diapause induced by
thermoperiodic regimes (Beck, 1987). Yi et al., (1986) incubated fat bodies of diapausing
fifth-instars larvae of O. nubilalis in vitro at 5 or 23 °C in Grace's medium and he determined
the glycerol contents of the organ and incubation medium. Fat bodies from diapausing larvae
chilled 3 weeks at 5 °C secreted glycerol into the medium at 5 °C at a net rate of approx. 0.75
nmol/mg fat body dry wt/h for at least 96 h while the tissue levels remained essentially
constant. Depending upon the experiment, from 6 to 15 times more glycerol was produced in
24 h at 5 °C by these fat bodies than by those taken from diapausing unchilled larvae and
incubated at either 5 or 23 °C. A minimal chilling period of 10–12 days was recognized as
necessary for chilled larval fat bodies to demonstrate rates of glycerol synthesis greater than
those of unchilled larvae and the lag showed a temporal correlation with changes in
haemolymph glycerol concentrations. These results suggested that this response to chilling by
O. nubilalis is relatively slow. While incubation, at 23 °C, of fat bodies from previously
chilled larvae did not result in cessation of glycerol secretion, the rate of its appearance in the
culture medium decreased during the 24-h incubation period. Although the ability of chilled
fifth-instar larvae to accumulate glycerol did not depend upon the diapause state results
showed that clearance of glycerol from the haemolymph by rewarmed O. nubilalis is related
to diapause intensity (Yi et al., 1986). Haemolymphatic trehalose concentration in the larvae,
high in winter, decreased in April, two months before the 50% pupation (Gadenne et al.,
1987). Maximum of the adult moths in the action sites was found in the last decade of June or
in the first decade of July in Slovakia (Cagan et al., 1995). The age-dependent cold hardiness
profile of O. nubilalisis compared between nondiapausing and diapausing larvae, as well as
with field-collected larvae. The results suggest that both cold tolerance and accumulation of
cryoprotectants depends upon the age of O. nubilalis larva. Late fifth-instar nondiapausing
larvae are more cold tolerant than younger fifth-instars because they show enhanced ability to
withstand sub-zero temperatures. No appreciable difference is observed between the
experimental groups of diapausing larvae as far as their supercooling ability and tolerance at
sub-zero temperatures above the supercooling point. In general, both field-collected and
diapausing larvae are more cold tolerant than nondiapausing larvae, indicating a direct link
between diapause and cold hardiness. The age of diapausing larvae affects the ability to
accumulate glycerol. Glycerol levels of 45-day-old diapausing larvae are significantly higher
(2.7-fold) compared with 90-day-old diapausing larvae. Moreover, diapausing larvae display a
five- to 13-fold higher glycerol content compared with nondiapausing larvae. There is a trend
for an age-dependent cold hardiness profile in O. nubilalis (Andreadis et al., 2008). The
implementation of maize with the event MON810 suggested the possibility of studying the
survival of larvae in old maize and some aspects of their diapause. To accomplish this, 6
maize cultivars, one with the event Bt176, two with the event MON 810 and the
corresponding three isogenics with neonate larvae of Sesamia nonagrioides and a natural
infestation of O. nubilalis were tested. The larvae of S. nonagrioides withdrawals from the
event Bt176 were supposed to be 14% of the total of larvae sampled for this species, whereas
25% was the total sampled for O. nubilalis. Nevertheless, in the varieties with the event MON
810, only 0. 25% and 1.9% of S. nonagrioides and O. nubilalis larvae were found,
respectively. The larvae gathered in the event Bt176 did not show differences in diapause
intensity. The effect of photoperiod in the completion of the diapause was different for both
species, the long photoperiod was accelerating the completion of diapause in S. nonagrioides
12
whereas darkness seemed to have a more pronounced effect in O. nubilalis (Perez et al.,
2008).
2.2.4. Influence of adult feeding on Ostrinia nubilalis stages
Males usually emerge a few days before females (Hagerman, 1997). Several studies have
demonstrated that water consumption by adults extended adult longevity and fecundity
(Caffrey, Worthley, 1927; Barlow, Muchmore, 1963; Schurr, Holdaway, 1966; Kira et al.,
1969; DeRozari et al., 1977), and more recent resuts demonstrate that sugar feeding by adults
also increases adult longevity and fecundity (Miller, 1988; Leahy, Andow, 1994). However,
the influence of adult feeding on progeny survival and behavior is not known (Andow, 2002).
Several authors (Barbosa, Capinera, 1978; Rossiter, 1991a, 1994; Fox, 1993, 1994) have
suggested that the nutritional condition of adults could affect the performance of immature
insects one or more generations later. Some characteristics such as egg size, which could be
influenced by the nutritional condition of adults, were heritable and their variation could be
correlated with the offspring survival (Rossiter, 1991a, b; Rossiter et al., 1993). Eggs hatch in
7 to 14 days, depending upon temperature (Guennelon, 1972; cit. Carter, 1984). The influence
of adult feeding of Trichogramma nubilale and larval competition within an egg of O.
nubilalis on progeny fecundity and longevity was tested. The number and sex of eggs
oviposited were determined through direct observations. Hind tibial lengths were measured on
females that were solitary or had shared a host egg with another T. nubilale. Females were
separated by size and provided either honey and excess hosts, honey and no hosts, no honey
and hosts, or no honey and no hosts each day for their lifetimes. The number of mature eggs
at eclosion was determined for several females by dissection of their ovarioles and counting
their eggs. The mean hind tibial lengths of solitary females was 0.18 mm, whereas females
that had shared a host egg with a male or female had hind tibial lengths of 0.14-0.16 mm.
Solitary females had 2.3 times more eggs and lived 1.2 times longer than females that had
shared the host with a male or female. Honey increased fecundity by factors of 1.6 and 1.9
and longevity by 5.4 and 4.8 days for solitary females and those that had shared a host egg,
respectively. Females that were not fed oviposited the same number of eggs as estimated from
dissected females at eclosion, suggesting that females mature additional eggs only if they are
fed as adults (Olson, Andow, 1998). Fadamiro and Baker (1999) tested the connection with
the pheromone-mating disruption of the O. nubilalis. A significant reduction in mating
frequency, as well as a marked delay in mating in feral females captured in disruptant-treated
fields, was recorded. In order to be able to accurately interpret the results in terms of effective
population control, the current study was undertaken on the effects of multiple matings and a
delay in mating on reproductive performance. Female O. nubilalis that mated at least twice
had a significantly higher fecundity and fertility, compared with once-mated females. In
addition, multiple-mated females deposited a significantly larger portion of their egg
complement, relative to single-mated or unmated females. Females that experienced a 3-day
delay in mating showed a significant reduction in fecundity compared with females that mated
soon after emergence. A 1-week delay in mating resulted in a further reduction in fecundity
and a near zero fertility. The effect of sugar feeding on reproduction was not significant. In
general, unmated females lived longer than mated females, and sugar-fed mated females had a
higher longevity than water-fed mated females (Fadamiro, Baker, 1999). Due to Andow
(2002) larval survival was higher when either the grandparental or parental generation had
fed, but the feeding sites of the surviving larvae were not affected by ancestral feeding
condition. This was the first evidence that grandparental feeding could influence larval
survival in the field. Larval movement was observed in the laboratory. Silking speed of
neonates was faster when either grandparents or parents had fed, while walking speed was
13
faster only when parents had fed. No broad-sense genetic correlation was found between
silking speed and walking speed. Broad-sense heritability among feeding histories were not
significant for silking speed, but was significantly greater than zero for walking speed when
grandparents fed and parents did not. These intergenerational effects could induce complex
population dynamics in this species (Andow, 2002). O. nubilalis is a polyphagous corn pest
species that includes two host races: one feeding on corn and one feeding on mugwort
(Artemisia vulgaris L.) and hop (Humulus lupulus L.). Being able to determine the type of
host plant on which field-caught moths fed as larvae would allow for the quantification of
mating rates within and between races, as well as the quantification of the spatial distribution
and oviposition of both races in the field. Ponsard et al., (2004) found that stable carbon
isotopes (δ13C) are a reliable indicator of host-plant photosynthetic type (C3 or C4)
regardless of adult food and intensity of metabolism; so even when food or metabolism had a
significant effect on wing δ13C values, the magnitude of this effect was too small to obscure
the signal characterizing host-plant type. Egg and spermatophore δ13C values similarly reflect
female and male host-plant type, respectively, regardless of adult feeding. Ponsard et all.,
(2004) found 224 host-plant species of O. nubilalis in the literature, including 19 species with
C4-type photosynthesis. However, in temperate areas, corn is probably the only significant C4
source of adult moths. Accordingly, wing δ13C values were more variable in field-caught
moths showing a typical C3-type δ13C value than in those showing a typical C4-type δ13C
value (Ponsard et al., 2004).
2.2.5. Role of sex pheromones and population structure
Insects of the order Hymenoptera are biologically and economically important members of
natural and agro ecosystems and exhibit diverse biologies, mating systems, and sex
pheromones. Ayasse et al., (2001) reviewed what is known of their sex pheromone chemistry
and function, paying particular emphasis to the Hymenoptera Aculeata (primarily ants, bees,
and sphecid and vespid wasps), and provide a framework for the functional classification of
their sex pheromones. Sex pheromones often comprise multicomponent blends derived from
numerous exocrine tissues, including the cuticle. However, very few sex pheromones have
been definitively characterized using bioassays, in part because of the behavioral
sophistication of many Aculeata. The relative importance of species isolation versus sexual
selection in shaping sex pheromone evolution is still unclear. Many species appear to
discriminate among mates at the level of individual or kin/colony, and they use
antiaphrodisiacs. Some orchids use hymenopteran sex pheromones to dupe males into
performing pseudocopulation, with extreme species specificity (Ayasse et al., 2001). Studies
of several species of moths have shown that males of these species fly in a sex pheromoe
plum using two behavioral mechanisms, optomotor anemotaxis (the use of visual information
for heading and groundspeed to stear a resultant track upwind), and an internal program of
self – steered counterturns. The combination of these two mechanisms during pheromone
mediated – flight is thought to shape the comonly observed zigzag – shaped flight tracks on
male moths flying upwind toward a pheromone source (Baker, 1989). This moth has been the
subject of much study of sex pheromones in Europe and North America. First because of its
pest status and a desire to find better ways to controlling it, and a second, because two
biotypes or so – called “strains”. That use distinct sex pheromone blends have been identified
within the described entity. One strain uses a blend of (Z) – 11 – tetradecenyl acetate (Z11 –
14:Oac) and (E) – 11 –tetradecenyl acetate (E11 – 14:Oac) in a ratio roughly 97:3,
respectively (so – called Z strain) (Klun et al., 1973), while the other uses the same chemicals
in the opposite ratio of 3:97 (So – called E strain) (Kochansky et al., 1975). Recently, Roelofs
et al., (2002) reported that females of the O. nubilalis, and the Asian corn borer, O. furnacalis,
14
had the genes for key desaturase enzymes that are involved in producing both species’
pheromone blends, but that in each species the gene for the related species is not expressed.
Female O. nubilalis use a 11-desaturase, which is common to many moths, and acts on a
chain-shortened 14-carbon fatty acyl chain to produce a mixture of (Z)- and (E)-11tetradecenoic acids. The acids are reduced and acetylated to give the pheromone components,
(Z)- and (E)-11-tetradecenyl acetates which have been described before (Roelofs et al.,
2002). In France Bourguet et al., (1999) investigated the inefficiency of pheromone traps to
control the O. nubilalis on hop crops. Evidence was gained for the existence of 2 O. nubilalis
strains with distinct sex pheromones. A hybrid population was also found. The population
present in hop fields appeared to be strain E and that on maize crops was found to be strain Z.
The strains differed according to either their choice of geographical location, or their specific
action on the host plant (Bourguet et al., 1999). Ngolo et al., (2000) studied the flight activity
based on the sex pheromones of O. nubilalis moths. His tests were based on comparing
pheromone trap types and within-field trap locations and its relationship to egg mass density
and crop damage in sweet maize in central Maine from 1995 to 1996. The use of both 3:97
Z:E-11-tetradecenyl acetate and 97:3 Z:E-11-tetradecenyl acetate pheromone blends studied
by Klun et al., (1973) confirmed that O. nubilalis in central Maine is attracted to both
pheromone lure types. O. nubilalis moths were captured predominantly with the E-lure type
than with the Z-lure type in both years. The Scentry Heliothis trap was more effective than the
Multi-Pher trap, but similar to the pheromone-baited water pan trap for monitoring O.
nubilalis flights. With the Scentry Heliothis trap, the grassy border and 1st maize rows were
the best locations for moth capture during the early flight period, but during the peak flight
period, traps located in the middle of the field caught the most moths. Maize damage was
recorded before moth captures in some sites and before egg mass counts in others, indicating
poor efficacy of traps for early flights. Significant and positive correlations were found
between moth captures in the midfield location and egg mass counts, and maize leaf damage,
and between egg mass counts and corn leaf damage. However, low coefficients of variation
suggested that pheromone trap captures were not good predictors of O. nubilalis leaf damage
in sweet maize (Ngoloet al., 2000). The moth adults are attracted to the microclimate of the
action sites. Free water collects in the grass from rain and dew is an important source of
drinking water for the moths (DeRozari et al., 1977). After obtaining water, females release
sex pheromone, mate, and subsequently move into attractive maize fields to oviposit
(Showers et al., 1976). Moths are known to aggregate in patches of dense vegetation. The
most sexual activity occurs up to 100 m away from the nearest cornfield in areas of dense
foxtaigrass (Shovers et al., 1976). Female moths produce and release species-specific sex
pheromone to attract conspecific males for mating purposes (Tang et al., 1987; Itagaki et al.,
1989), O. nubilalis males have hair pencils located ventrally on the 8th sternite and these are
axtruded when a male approaches a calling female (Royer, McNeil, 1992). The production of
sex pheromone in a number of moth species follows a diel rhythm which may be regulated by
neutral (Tang et al., 1987; Itagaki et al., 1989), neuroendocrine (Raina, Klun, 1984) or
hormonal factors (Cusson, McNail, 1989). Among these three regulatory mechanisms,
neuroendocrine regulation of sex-pheromone biosynthesus have received much attention in
recent years. An active factor, PBAN (pheromone biosynthesis activating neuropeptide), was
isolated from H. zea (Noctuidae) and shown to be a 33 amino acid peptide (Raina et al.,
1989). Using an in vitro bioassay, PBAN was shown to stimulate pheromone production in a
number of moth species (Raina et al., 1989). Female of O. nubilalis use a mixture of (Z)-11and (E)-11-tetradecenyl acetate as their sex pheromone. The production of sex pheromone in
O. nubilalis also appears to be under the control of a PBAN-like factor (Klun et al., 1973;
Ma, 1992). Decapitation of female causes a rapid decline in the sex pheromone to a nondetecable level in 24 h. Injection of a crude extract of the brain-subesophageal ganglion
15
complex or of 4 pmol of Hez- or Bom-PBAN I into the decapitated females restores the
pheromone titer to that comparable of a normal female within 3 h (Ma, 1992). In vitro
pheromonotropic action of Bom-PBAN on isolated ECB sex-pheromone gland has a specific
and dose-depended requirement for physiological concentrations of calcium. Sex pheromone
production stimulated by Bom-PBAN is inhibited when the pheromone gland is incubated in
medium lacking calcium, and blocked in the presence of lanthanum, which is a potent calcium
channel blocker. This requirement for calcium is specific and can not be replaced by another
divalent ion, magnesium. The calcium ionophore, A23187 mimics the action of PBAN by
stimulating pheromone production. Ma and Roelofs were able to stimulate sex pheromone
production in isolated O. nubilalis pheromone glands with synthetic Bom-PBAN using a
dose as low as 0.25 nM. These results corroborated others that show that PBAN acts directly
on the sex pheromone gland to stimulate sex-pheromone production (Ma, Roelofs, 1995).
Fadamiro and Baker (1999) in their tests studied pheromone-mating disruption of the O.
nubilalis. They recorded a significant reduction in mating frequency, as well as a marked
delay in mating in feral females captured in disruptant-treated fields. In order to be able to
accurately interpret the results in terms of effective population control, the current study was
undertaken on the effects of multiple matings and a delay in mating on reproductive
performance. Females O. nubilalis that mated at least twice had significantly higher fecundity
and fertility, compared with once-mated females. In addition, multiple-mated females
deposited a significantly larger portion of their egg complement, relative to single-mated or
unmated females. Females that experienced a 3-day delay in mating showed a significant
reduction in fecundity compared with females that mated soon after emergence. A 1-week
delay in mating resulted in a further reduction in fecundity and a near zero fertility. The effect
of sugar feeding on reproduction was not significant. In general, unmated females lived longer
than mated females, and sugar-fed mated females had a higher longevity than water-fed mated
females (Fadamiro, Baker, 1999). Examination of sequence variation at nuclear loci could
give insights into population history and gene flow that cannot be derived from other
commonly used molecular markers, such as allozymes. The O. nubilalis has been divided
into three races in New York State on the basis of differences in pheromone communication
and life history. Previous allozyme data have suggested that there is a small but significant
amount of genetic differentiation between these races. The Pheromone-binding protein (PBP)
did not appear to be involved in the pheromone differences between these races. Examination
of variation at the PBP locus in the three races reveals no fixed differences between races
despite high levels of polymorphism. There also appears to have been considerable
recombination in the history of the pheromone-binding protein alleles. Observation of both
recombination between alleles and lack of significant nucleotide or insertion/deletion
divergence between races leaded to suggest that these populations are either recently diverged
or have continued to exchange genetic material subsequent to divergence in pheromone
communication and life history (Willett, Harrison, 1999). Frolov (1994) studied the structure
of populations of O. nubilalis, O. narynensis, O. scapulalis and O. persica [O. nubilalis
persica] on dicotyledonous fodder crops. Test were conducted in 1976-92 in over 60 localities
in the European and 5 in the Asiatic part of former USSR with reference to the hereditary
factors determining morphological characteristics (Mt and i) of the male tibiae. In
confirmation of the author's earlier conclusions - that distribution of the pyralids must be
viewed against the background of a real or potential polymorphic population structure, wide
areas occupied by practically monomorphic populations were found to alternate with
territories occupied by polymorphic ones. Changes in gene concentration from near 0 to near
1 were observed within distances of about 50 to 60 km. The observed alternation of
population structures correlates with precipitation gradients. The values for average
precipitations in June and in May-August as well as those for the hydrothermal coefficient for
16
June differ significantly for areas occupied by different species. The zones where the average
precipitation in June is no less than 77 mm are inhabited by O. nubilalis, those where it is 5577 mm like wise by O. narynensis and O. scapulalis (the former being somewhat more
moisture-loving than the latter) and those where it is less than 50 mm by O. persica. The areas
with intermediate precipitation values were occupied by polymorphic populations (Frolov,
1994). Mixing the sex pheromones of the Sesamia nonagrioides, and the O. nubilalis, results
in significantly lower captures of O. nubilalis when compared to traps loaded with its
pheromone alone. Rubber septa loaded with a constant concentration of the pheromone of O.
nubilalis and different percentages of the S. nonagrioides pheromone (from 1 to 100%) causes
dose-dependent antagonism in the field. Electroantennograms of O. nubilalis males showed
high antennal responses to its own pheromone components, followed by smaller responses to
the major, [(Z)-11-hexadecenyl acetate (Z11-16:Ac)], and two minor components [dodecyl
acetate (12:Ac) and (Z)-11-hexadecenal (Z11-16:Ald)] of the S. nonagrioides pheromone.
There was almost no response to the S. nonagrioides minor component (Z)-11-hexadecenol
(Z11-16:OH). Field tests that used traps baited with the O. nubilalis pheromone plus
individual components of S. nonagrioides showed that Z11-16: Ald causes the antagonism.
Adding 1% Z11-16:Ald to the pheromone of O. nubilalis reduced oriented flight and
pheromone source contact in the wind tunnel by 26% and 83%, respectively, and trap captures
in the field by 90%. The other three pheromone components of S. nonagrioides inhibited
pheromone source contact but not oriented flight of O. nubilalis males and did not inhibit
capture in the field. Cross-adaptation electroantennogram suggests that Z11-16:Ald stimulates
a different odor receptor neuron than the pheromone components of O. nubilalis. Z11-16:Ald
is a potent antagonist of the behavioral response of O. nubilalis (Gemeno et al., 2006).
Dominigue et al., (2006) used the cut-sensillum technique to assess the effect of both adult
age and egg-to-adult development time on olfactory neuron responses of Z strain moths of the
O. nubilalis. Compounds tested included the pheromone components, (Z)-11-tetradecenyl
acetate and (E)-11-tetradecenyl acetate, the behavioral antagonist, (Z)-9-tetradecenyl acetate,
and components of the O. furnicalis (Asian corn borer) sex pheromone, (Z)-12-tetradecenyl
acetate and (E)-12-tetradecenyl acetate. The proportion of moths having neurons responding
to the two O. nubilalis sex pheromone components and antagonist increased with longer
development time and age. The spike frequency of neurons responding to (E)-11-tetradecenyl
acetate and the antagonist increased with longer development time. Fourteen of 45 moths with
neurons sensitive to either of the O. nubilalis pheromone components responded to (Z)-12tetradecenyl acetate or (E)-12-tetradecenyl acetate. The likelihood of (Z)-12-tetradecenyl
acetate stimulating a neuron similar in spike shape and waveform to that responding to (E)11-tetradecenyl acetate increased with development time (Dominigue et al., 2006). A flight
tunnel study showed that 3-5% of O. nubilalis (Z/E11-14:OAc), could fly upwind and make
contact with sources releasing the sex pheromone of the related Asian corn borer (ACB), O.
furnacalis (2:1 Z/E12-14:OAc). Linn et al., (2007) showed that rare males (3-4%) are also
present in South Korean ACB that respond to the sex pheromone blends of the ECB UZ (97:3
Z/E11-14:OAc) and BE (1:99 Z/E11-14:OAc) pheromone races. We also show that the
upwind flight response of a significant proportion of male ACB was antagonized by the
addition of 1% Z9-14:OAc to the ACB blend, a compound that also antagonizes the upwind
flight of ECB males. Male ACB flight behavior was not, however, affected by adding either
of the ECB blends to the ACB blend, or by the addition of 50% 14:OAc, a compound
identified from female pheromone glands of ACB and a number of other Ostrinia species.
Additional flight tunnel tests with ACB to study the comparative aspects of ECB and ACB
pheromone response specificity showed that male ACB exhibited maximal levels of upwind
flight and source contact with doses of pheromone (30 and 100 micro g on rubber septum
sources) that also elicited maximal levels in the two ECB pheromone races. The maximal
17
level of source contact for ACB (66%) was lower than observed with the UZ race of ECB to
its pheromone blend (>95%), but comparable to those for the BE race of ECB (65-70%).
Male ACB also flew upwind in high proportions to a broader range of ratios of Z/E12-14:OAc
(80:20 to 20:80) than was previously observed for either of the ECB races (Linn et al., 2007).
Periodicity of pheromone titre in female moths, modulated by various factors (age,
photoperiod, temperature), has been reported for a number species, however, comparative
studies on pheromone strains of those species where pheromone polymorphism is known to
occur has so far scarcely been studied. In study made of Karpati et al., (2007), the rhythm and
age dependence of calling behaviour as well as of the titre of the respective main sex
pheromone components, and timing and frequency of mating within E-and Z-strains of O.
nubilalis were compared during scotophase, under laboratory conditions (18/6 hours
photoregime, 26 deg C). Very similar trends were fund in both strains in the diel fluctuation
of both calling behaviour and pheromone titre within the scotophase, as well as its age
dependence, and also in timing and mating frequency. The titre of the respective main
pheromone component gradually increased during the scotophase. Highest titers were found
in freshly emerged females, however even 6-day-old females produced roughly half amounts.
Freshly emerged females of both strains were ready to mate with males of their own strain,
however, the percentage of matings were higher in 1-3-day-old age cohorts. Differences
between strains was found in the total amount of the respective main pheromone components
in the gland. The average amount of (Z)11-tetradecenyl acetate extracted from the ovipositor
of Z-strain females 10 min. before the end of the scotophase was 2.17 ng/female equivalent,
whereas the corresponding value of (E)11-tetradecenyl acetate for E-strain females was 8.25
ng/female equivalent. Moreover, E-strain females tended to start calling somewhat earlier,
and the percentages of calling females was higher during the peak calling period than that of
the Z-strain (Karpati et al., 2007). Isomeric mixture of 11-tetradecenyl acetate with the Z/Econformation in a 95:5 ratio that was extracted from the peritoneal cavity of male O. nubilalis
in Xinjing (PRC) (Li et al., 2008).
2.2.6. Choice of oviposition site
Chemical analyses of leek leachates show a large variety of metabolites as already observed
on different plant species (maize, sunflower, tansy ragwort), especially free amino acids and
soluble carbohydrates. Leek leachates 1) permit leek discrimination from other plant species
by free amino acids proportions, 2) show caracteristic unknown ninhydrine positive
substances and 3) higher levels of fructose, glucose and sucrose than leachates from young
maize plant. These last substances, known to be active in the oviposition site preference of the
generalist lepidoptera O. nubilalis, are still active in the host oviposition preference between
leek and young maize plant. However, the highest number of eggs masses laid on reek leaves
come off, and first instar larvae do not feed (Derridj, 1996). In the maize – belt, first flight of
females were attracted to the tallest maize plants in the area of oviposit on early planted
maize (Showers et al., 1989). Second flight females were attracted to late planted fields and
oviposit on silking and tasseling plants (Everett et al., 1958; Showers et al., 1989). Plant
maturity is an important factor in the choise of oviposition site and O. nubilalis females
reportedly were able to discriminate between maize plants differing in only a few days
development (Huber et al., 1928). If maize is comercial vegetable growing areas has
progressed beyond the silking and tasseling stage, females have moved to more attractive
alternative hosts (Shovers et al., 1989). Proponents of organic farming have been long
suggested that their methods produce "healthy" crops that are less susceptible to insects and
diseases. Experimental comparisons of O. nubilalis egg-laying response to maize plants
grown in a greenhouse in soil collected from either organically or conventionally managed
18
farms provided evidence consistent with these assertions. In each of three paired comparisons,
higher egg-laying occurred on plants in conventional soil. Subsequent studies suggested that
differences in ovipositional preference were related to plant-mineral balance; a three-mineral
quadratic model showed strong predictive power for O. nubilalis oviposition. A role for plant
minerals was also suggested in a study of paired maize fields with high and low O. nubilalis
populations compared at three different geographic locations. Significant differences in leafmineral profiles between fields were measured that were consistent across locations. Based on
these cumulative findings, it is hypothesized that: (1) maize plants with an optimal mineral
balance show lower susceptibility to insect pests, (2) determining the effects of minerals on
susceptibility must include consideration of both ratios and absolute levels, and (3) a more
resistant physiological state is more likely in organically managed soils because of the
inherent greater capacity of these soils to buffer availability of minerals to plants (Phelan,
1997). For young maize in the early whorl stage, when maize plants are up to 40 cm tall, the
maize plant itself may increase their mortality rate using a chemical called DIMBOA. This
natural plant chemical reduces corn borer feeding and increases the tendency of small
caterpillars to leave the plant. DIMBOA is one of the factors responsible for the so called
"natural resistance" of certain maize hybrids. Unfortunately, it dissipates as the plant grows
and is of no real value by the late whorl stage (Hagerman, 1997). The ability to attract adults
to aggregation sites also could be important to producers. Refuge crops planted near O.
nubilalis aggregation sites probably will attract high levels of adult oviposition. This would
increase the refuge value of these plants. Aggregation sites also could be strategically placed
to encourage rare resistant moths to mate with susceptible moths. According to Hellmich et
al., (undated) results from 1996, suggested that oat and switchgrass are excellent firstgeneration O. nubilalis aggregation plants; German millet is the best second-generation
aggregation plant (Hellmich et al., undated). Oviposition by O. nubilalis, was examined by
Apangler et al (2003) in relation to sweetcorn development from 1994 to 1996 in
Pennsylvania, USA, and related to harvest infestation levels. Stepwise multiple regression and
linear regression showed that 79-87% of the variability of larvae per ear or proportion of ears
infested at harvest was explained by the number of egg masses laid from about anthesis to
brown silk stages. The analyses indicated three periods of oviposition with differing
implications to harvest infestation level: (1) eggs laid from 784-337 degree-days (DD) before
harvest (before green tassel) had very low correlation to harvest infestation; (2) eggs laid from
336-169 DD before harvest (green tassel to green silk) were highly correlated with harvest
infestation; and (3) eggs laid during the last 168 DD of sweetcorn development (green silk to
harvest) had low to moderate correlation with harvest infestation. The 336-169 DD period
corresponded to the anthesis to brown silk growth stages, which was approx equal to 14-21
days long, and would be the likely period for optimum chemical control (Spangler et al.,
2003). Effects on O. nubilalis oviposition were assessed directly by counting egg masses and
indirectly, through assessment of the damage done to corn stalks resulting from O. nubilalis
infestations. The impact of weeds on the main generalist predators in this system was
quantified through direct counts and predation trials on sentinel egg masses. In this study,
altering the timing of herbicide application in herbicide-resistant field maize did not appear to
affect the oviposition preference of O. nubilalis or the beneficial insects that prey on its egg
masses. End-of-season stalk comparisons showed no differences in O. nubilalis infestation
levels among the treatments. Predation on sentinel egg masses showed few significant
differences among treatments, and predator densities were only rarely significantly different
by treatment and showed no evident trends (Wilson et al., 2004). ECB larvae detect and avoid
feeding in the presence of phytoecdysteroids (PEs) such as 20-hydroxyecdysone (20E).
Therefore, we hypothesized that females would have taste receptors similar to larvae and
avoid laying eggs in the presence of 20E. Calas et al., (2007) found female-specific taste
19
sensilla on the tarsi that respond to 20E at concentrations as low as 10-6 M, a threshold
comparable to that of larvae. However, in choice tests, females laid a similar number of eggs
on 20E-treated and on nontreated artificial substrates (filter paper, glass, and nylon), although
they spent significantly more time in behavioral sequences related to substrate assessment
when 20E was present. In contrast, when given a choice between maize plants (eight leaves)
sprayed with 20E or only the solvent, females laid 70% fewer eggs on the treated than on
control plants. These observations suggest that other chemical cues of plant origin must be
present at the same time as 20E for females to modify their oviposition behaviour (Calas et
al., 2007). Changes in host preferences are thought to be a major source of genetic divergence
between phytophagous insect taxa. In western Europe, two sympatric taxa, O. nubilalis and
O. scapulalis, feed mainly on maize and hop or mugwort, respectively. These two species
may have diverged without geographic isolation after a host shift of ancestral populations
onto maize or another cultivated species (e.g. sorghum). A previous study using inbred
laboratory strains revealed that the two species differ in their oviposition choices in maizemugwort tests. Malausa et al., (2008) sampled four natural populations in France (two of each
taxon) and tested their oviposition behaviour toward four of their main host plant species:
maize, sorghum, mugwort and hop. O. nubilalis females showed a very high preference for
laying their eggmasses on maize, whereas O. scapulalis females displayed a more balanced
range of preferences. O. nubilalis females were attracted slightly to sorghum, suggesting that
this plant is an accidental, rather than a regular and ancestral host plant of O. nubilalis. One
important result arising from this study is the significant proportion of eggs laid by both
Ostrinia species on hop. This may explain why some stands of hop are sometimes not only
infested by O. scapulalis but also by O. nubilalis larvae, a situation preventing assortative
mating based on microallopatry. Hence, further studies must be conducted to see whether the
host preference in the genus Ostrinia might be linked to assortative mating by a mechanism
that is not mediated by the host plant (Malausa et al., 2008). Oviposition behaviour and egg
distribution of O. nubilalis is reviewed based on published information and new research
made by Suverkropp et al., (2008). The position of egg masses of O. nubilalis on maize plants
and leaves were sampled in the field. Most egg masses were found on the lower leaf side, on
the middle part of the leaf or close to the stem, and close to the mid-rib. Direct observations of
oviposition behaviour were made in laboratory and field cages. O. nubilalis moved very little
on the plants and only 10% of the females that landed on the plants oviposited. The number of
actual ovipositions was quite low compared to the number of landings, with females walking
only a few centimetres if at all. Shed scales of adult moths were not abundant near egg masses
with only 37% of egg masses associated with scales and 45% with only a few scales. Many
scales were found on other places of the plants. At the leaf and plant level, scales might serve
as a useful host-cue to Trichogramma brassicae, an egg parasitoid of O. nubilalis. However,
scales are not an indicator for the presence of egg masses in their immediate vicinity
(Suverkropp et al., 2008).
2.2.7. Damage of maize caused by Ostrinia nubilalis
O. nubilalis is serious pest of both sweet maize and grain corn, and before the availability of
modern insecticides this insect caused very marked reductions in corn production (Cagáň,
1993; Capinera, 2000). Corn borers feed on all parts of the corn plant except the root. Their
damage leads to physiological yield loss, harvest yield loss, loss of quality and loss from
secondary pests (Hagerman, 1997). Young larvae feed on tassels, whorl and leaf sheath tissue;
they also mine midribs and eat pollen, that collects behind the leaf sheath. Sometimes they
feed on silk, kernels, and cobs, or enter the stalk. Older larvae tend to burrow into the stalk
and sometimes the base of the corn ear, or into the ear cob or kernels. Feeding by older larvae
20
is usually considered to be most damaging, but tunnelling by even young larvae can result in
broken tassels. The presence of one to two larvae within a corn stalk is tolerable, but the
presence of any larvae within the ear of sweet corn is considered intolerable by commercial
growers, and is their major concern. Heavily tunnelled stalks of grain corn suffer from
lodging, reducing the capacity for machine harvesting. Lodging is not a serious threat to sweet
corn. Most yield loss can be attributed to the impaired ability of plants to produce normal
amounts of grain due to the physiological effect of larval feeding damage in leaf and
conductive tissues (Cagan, 1993; Capinera, 2000). Harvest yield loss results when stalk or
shank breakage leads to less efficient harvesting. Grain is there but the combine doesn't pick it
up. Harvest yield loss is greatest with weak-stemmed hybrids and increases when late
harvesting and/or adverse weather lead to more lodging in the field (Hagerman, 1997).
Damages of O. nubilalis are very suitable enter gate for pathogenic fungies (Cagan, 1993;
Capinera, 2000). The most important secondary pests are ear molds and stalk rot organisms.
These diseases can enter through corn borer entry holes. Ear molds may cause the grain to be
downgraded as it is less suitable as livestock feed. Some ear molds produce mycotoxins which
cause adverse reactions in livestock at very low levels. Stalk rot organisms accelerate stalk
deterioration, leading to reduced carbohydrate transport during grain fill (more physiological
yield loss) and more lodging. Other secondary pests which may follow a corn borer
infestation include sap beetles and birds. The latter can potentially cause extensive grain
losses (Hagerman, 1997). O. nubilalis larvae also damage both the stem and fruit of beans,
pepper, and cowpea. In celery, potato, rhubarb, Swiss chard, and tomato, it is usually the stem
tissue that is damaged. In beet, spinach, and rhubarb, leaf tissue may be injured. Entry of
borers into plant tissue facilitates entry of plant pathogens. The incidence of potato blackleg
caused by the bacterium Erwinia carotovora atroseptica, for example, is higher in potato
fields with stems heavily infested by corn borers. Direct damage by corn borers to potato
vines, however, results in negligible yield loss (Capinera, 2000). Losses caused by the pest O.
nubilalis range from 250-1000 kg/ha, depending on the degree of infestation, year, and yield
averages. This fact justifies protection measures in Hungary on the whole of the seed
production and sweetcorn fields, and on 40% of the commercial maize production areas. In
addition to direct damage, indirect losses are also considerable, since the injuries caused by
the pest facilitate infection by Fusarium species. For these reasons, it is worth reviewing the
biology and behaviour of this pest, the extent of the economic loss resulting from the damage,
and the methods of controlling it (Szoke et al., 2002). The effects of the O. nubilalis on the
protein, fat and starch content of maize hybrids Colomba, Occitan and DK-471 were
determined in a field experiment conducted in Hungary during 2001. Infestation with ECB
reduced the cob weight of the hybrids examined. Fat, protein and starch content in the kernels
of the hybrids also decreased with ECB infestation (Takacs, 2002). In maize, the timing of
vegetative phase transition from juvenile to adult vegetative phases can be modified through
selection. A reduction in the juvenile vegetative phase has been associated with resistance to
diseases and pests. The major maize pest in temperate areas is O. nubilalis and in Europe
Sesamia nonagrioides Lefebvre. The objective of study was to determine the effects of
divergent selection for the timing of vegetative phase transition in maize on resistance to corn
borers. Three cycles of divergent selection for early and late phase transition in a field corn
synthetic and in a sweet corn population were evaluated separately under S. nonagrioides and
O. nubilalis artificial infestation. For the field corn experiment, yield and moisture improved
with selection for phase transition in both directions, but improvement was due to artifacts of
selection, rather than to the change in phase transition. There were no correlated responses for
corn borer damage, yield, or grain moisture due to selection for the timing of vegetative phase
transition. In the sweet corn experiment, selection for the timing of vegetative phase transition
had no significant effects on corn borer damage in sweet corn harvested at the fresh stage.
21
Results did not support the use of phase transition as an indirect criterion for improving
resistance to corn borers in maize. The relationship between phase transition and pest
resistance reported by other studies could depend on the genotypes or could be too weak to be
detected in a selection programme with wild-type maize (Revilla et al., 2005). A study was
conducted in 2000-2002 at field sites in central and western Kentucky to investigate whether
infestation by O. nubilalis differentially affects the production of high-oil corn compared with
traditional field corn. Statistical differences in grain weight and percentage of oil content
between the five infestation levels were significant at both locations and for all years. Average
grain yield was reduced by 0.40% and average oil concentration by 0.011% for each 1% of
damaged plants, and there was a strong correlation (0.76) between leaf damage ratings (i. e.,
Guthrie scale) and yield reduction. In general, corn planted at the early planting date tended to
have a higher yield (grain weight) and oil content (Quinton et al., 2005).
2.3. Ostrinia nubilalis in Slovakia
The native area of occurrence O. nubilalis is Europe, the north part of Africa and some places
of south-east part of Asia. Periodical occurrence we can find in Slovakia too (Cagáň, 1993 a).
The European corn borer, O. nubilalis, is the most important maize pest in Slovakia and is
responsible for considerable yield loss each year (Cagáň, Grenčík, 1990).
The weight of O. nubilalis larvae was investigated during 1991-92 in Slovakia on 17 inbred
lines of maize. No significant differences in the weights of larvae developed on different
genotypes were found under natural infestation, while artificial infestation resulted in
significant differences. However, a selection of maize genotypes based on the weight of
larvae did not guarantee better pest resistance (Cagan, 1997). Spring behaviour of larvae of
the O. nubilalis was observed in south-western Slovakia during 1989-96. The number of
larvae in maize stems covered with soil and in intact maize stems was compared. The first
larvae of the ECB were found on the soil surface from 16 March to 23 April (depending upon
the year). The highest spring movement of the ECB larvae was found in the second half of
April. Soil temperature was the main factor influencing the movement of the larvae, which
were active even at temperatures below 10 deg C. High rainfall in the first half of April 1990
and in the second half of March 1992 forced some larvae to the soil surface. The time interval
between spring movement of the ECB larvae and their pupation was nearly 2 months. The
time of pupation did not correlate with the time of spring movement of larvae. Analysis of the
remnants of maize stems covered with soil showed that all larvae abandoned their winter
shelters during spring. The number of larvae in new shelters (made from corrugated paper)
was almost half the number of larvae surviving in intact maize stems on the surface of the soil
(Cagan, 1998 a).
Light-trapping of adults of O. nubilalis in maize fields in southern Slovakia, Czechoslovakia,
in 1973-83 indicated the occurrence of a partial 2nd generation of the pest, in which larvae
failed to complete their development, in years with above-average temperatures. The
abundance of the pest was highest in the years in which this partial 2nd generation occurred,
and reached the economic threshold mainly in years in which the average daily temperature in
May-August exceeded 19 deg C (Barabas et al., 1985). In a field study in 1987-95 in
Slovakia, the occurrence of the second generation of O. nubilalis was investigated. More than
30000 larvae were found in maize stalks in autumn. In 1994, for the first time in Slovakia,
pupal cases were observed in stalks, indicating the development of the second generation
adults of the pest. This was largely related to temperature. Minimum daily temperatures in
July 1994 never dropped below 12 deg C (Cagan, 1998 c). During monitoring of O. nubilalis
populations on maize in 1956-59, there were an average of 250-310 eggs/100 plants, at the
peak of oviposition. Of these eggs, 35-80% were parasitized by Trichogramma evanescens.
22
Irregular inspections were performed in 1980-85 for the presence of eggs of O. nubilalis at
various sites with intensive maize cultivation. Average occurrence of eggs per 100 plants
ranged from 47 to 147 and the levels of parasitism by T. evanescens were 0.0-43.4% at one
site in 1980, 0 in the same place in 1981, 1.6% in 1983 and 0 in 1984. The average occurrence
of O. nubilalis eggs per 100 plants was much lower in 1980-85 than in 1956-59, but natural
parasitism by T. evanescens had decreased to a minimum (Birova, 1988). Studies on
infestation made by Cagan and Grencik (1990) of 5 maize hybrids by O. nubilalis carried out
in 7 localities in the former Czechoslovakia in 1986-88 showed that when the percentage
infestation in a stand was no higher than 80% the damage to the infested plants was about the
same. The average numbers of holes in the stems and of damaged ears per infested plant
increased only when infestation increased beyond this (Cagan Grencik, 1990). On the basis of
observations in 1991-1993 was found, that in Slovakia there are the locations with permanent
high ocurence of the O. nubilalis. In western Slovakia were these locations in hilly region
with altitute 170-220 m and in eastern Slovakia also in plains with the altitude nearly 100 m.
Average yearly temperature at the locations with high occurrence of the O. nubilalis was in
western Slovakia 9-9.4 °C and in eastern Slovakia 9-9.7 °C. The highest occurrence of the
pest was found at the locations with nearly 600 mm rainfall per year. The area with the
highest occurrence of the O. nubilalis corresponded to the warm and moderate dry climatic
area (the number of summer days in year above 50, moisture index acc. (Konček, 1980;
Cagáň et al., 1995), from –20 to 0). Climatic moisture coefficient (Tomlain, 1980; cit. Cagáň
et al., 1995 ) in these area was 200 – 300 mm and sum of average daily temperatures above 10
°C was 2800-3000 °C in the western Slovakia and 2800 - 3100 °C in the eastern Slovakia.
Weather conditions also influenced the occurrence of the pest. There was found very strong
positive correlation between the sum of rainfall in the period 21 days with maximum increase
of leaf damage caused by O. nubilalis larvae and percentage of damaged plants in autumn.
Maximum of the moths in signalization cages was found usually sooner than their maximum
in action sites. Maximum of the moths in the action sites was found in the last decade of June
or in the first decade of July. The first eggs of the pest on the maize plants were found usually
in the third or second decade of June respectively. Egg laying maximum was observed either
at the end of June or at the beginning of July. The first damages of maize leafs caused by the
ECB larvae were usually found in the first decade of July (Cagáň et al., 1995). In 1994, for
the first time in Slovakia, pupal cases of O. nubilalis were observed in stalks, indicating the
development of second generation adults of the pest. Degree-days accumulation during the
whole year was 1545.3 °C (Cagáň, 1998). According to Tancík and Cagáň (2004) the first
moths in cages were found in the middle of June and their maximum was found in the last
decade of June or at the beggining of July. The first egg masses on the maize plants were
found usually in the second half of June. At the time of the first O. nubilalis eggs, the sum of
temperaturesabove 10 ºC was 400-450 ºC. Maximum of egg laying occured at the end of June
or at the begining of July, 3-4 weeks after the maximum of adults in cages. During this time
the sum of temperatures above 10 ºC was 530-580 ºC. The last egg masses on the maize
plants were generally observed at the end of the second decade of July. The first damage
caused by O. nubilalis larvae was found during the time of the maximum egg laying. The
period between the first eggs andthe leaf damage was nearly two weeks (Tancík, Cagáň,
2004).
In a field study in 1989-95 near Nitra in southwestern Slovakia, the incidence of O. nubilalis
eggs was observed on maize plants. At the beginning of the egg-laying period, the clusters
were usually found on the 4th and 5th lower leaves, whereas during the peak egg-laying
period, the clusters were mostly observed on the 5th-7th leaves. The eggs were found on the
lower maize leaves in 1992, 1993 and 1994 when the first eggs were observed earlier in the
season. Height above soil level of the egg clusters was not influenced by average daily
23
temperatures. During wet seasons, eggs were laid higher up the plants. Over seven years, the
mean number of eggs in one cluster ranged from 15.03 to 18.24. The average number of eggs
in one cluster during all years of observation was 16.66. Analysis of variance did not show
significant differences due to year. The correlation coefficient between mean number of eggs
in one cluster and average daily temperature was r = -0.686 (p = 0.08894). A very strong
correlation was obtained between the amount of eggs observed on the maize plants and the
percentage of damaged plants in autumn (r = 0. 894, p = 0.00662) (Cagan, Tancik, 1996).
Experiments to study the phenology of O. nubilalis were carried out at three locations near
Nitra, Slovakia, in 1987-91. The first moths in the cages emerged during the first half of June,
and in the field at the end of June. The maximum moth number in the cages occurred 11 days
earlier, compared with the maximum of the flight in the field. The first egg masses on maize
plants were usually observed at the end of June. The average maximum of moths in the field
was observed on 7 July (ST10 = 519 deg C), and the average date of the greatest occurrence
of the eggs was 8 July (ST10 = 524 deg C). The first evidence of leaf damage caused by the
ECB larvae was found on average on 9 July (ST10 = 531 deg C). Mean date of the first stalk
damage was 18 July (Cagan, Barabas, 1996 b).
From 1989-92 the damage caused by the O. nubilalis larvae to maize plants was observed in
southwestern Slovakia. The first damage was usually found in the upper internodes of the
plants. Larval entrance holes were found at a higher position at the first date of observation as
compared to the second and the third dates (one week later or in autumn). The highest amount
of larval entrance holes was found in internodes 7, 8 and 9. The plants sown earlier were
damaged on a lower internode than the plants sown later (Cagan, 1998 b). Natural parasitism
of the O. nubilalis eggs by Trichogramma was assessed in 1993 to 1996 in south-western
Slovakia. No parasitized eggs were found in 1993. In 1994, parasitized ECB eggs were
observed on July 7th, July 11th and July 13th. The average percentage of egg parasitism was
3.86 and 1.54 at two locations. Only one parasitized egg cluster was observed at the beginning
of the ECB egg laying in 1995. At the end of the egg laying period (10th, 13th, 17th and 24th
July), parasitism varied between 1.29 and 100% and averaged 4.15% at the location NitraMalanta. Parasitism was high in 1996 at the location Nitra-Malanta and reaching an average
of 15.21%. Parasitized eggs were detected throughout the ECB egg laying period. At NitraJaníkovce in the same year, average parasitism reached 2.46%. It was assumed that extremely
dry weather probably reduced the egg parasitoid populations in 1993-95. The egg parasitoid
species was identified as Trichogramma evanescens. The study showed that the egg parasitoid
appears sporadically in maize fields, was often absent but sometimes occurred in low numbers
in spring, early summer and increased towards the end of the season. Therefore, the release of
mass reared Trichogramma can be recommended to ensure predictable biological control of
the pest (Cagan et al., 1998). Eriborus terebrans [Diadegma terebrans], a parasitoid of the O.
nubilalis, was studied at four locations in central Europe during 1993-95. Regular parasitism
of O. nubilalis was found only at Blatnice in Moravia (eastern part of the Czech Republic). At
this location, the parasitism was 2.22% in 1993, 0.47% in 1994 and 0. 06% in 1995. In 1994
and 1995, low parasitism (0.56 and 0.12%, respectively) was found at Král'ovský Chlmec
(eastern Slovakia). The records are the first from the Czech Republic and Slovakia. The
parasitoid was not found at Nitra (south-western Slovakia) and Wroclaw (south-western
Poland). The first cocoons of D. terebrans developed in the first half of June. Parasitoid adults
emerged from mid-June to mid-July. Results showed complete coincidence between
bionomics of D. terebrans and bionomics of its host O. nubilalis (Bokor, Cagan, 1999). The
occurrence and phenology of S. turionus was studied between 1993 and 1996 at Král'ovský
Chlmec and Nitra (Slovakia), Blatnice (Czech Republic) and Wroclaw (Poland). Parasitism of
O. nubilalis, collected from maize crops, reached rates of 0.76-2.04% at Nitra, 0.24-2.72% at
Král'ovský Chlmec and 0.88-2.78% at Blatnice. S. turionus was not found at Wroclaw.
24
Parasitoids did not develop until the end of July. S. turionus pupae developed in October. S.
turionus adults emerged during 17-31 March in 1994, 27 March to 11 April in 1995 and 21-27
April in 1996. The developmental threshold temperature for 50% adult emergence was 0 deg
C and the respective thermal constant was 358.2-390.3 deg C day-degrees. Under laboratory
conditions, there were a minimum of 2 S. turionus generations per year. It is concluded that S.
turionus is of little significance in the biological control of O. nubilalis in Central Europe
(Cagan, Bokor, 1998). Phenology, bionomics and parasitism of Microgaster tibialis, a
parasitoid of the O. nubilalis, was studied in four regions of Central Europe in 1993-95.
Regular parasitism of O. nubilalis larvae (1.83-2.95%) was observed at Blatnice in Moravia
(eastern part of the Czech Republic). Parasitoid cocoons were also found in SW Slovakia and
E Slovakia during 1994-1995 and at Wroclaw (SW Poland) in 1994. These records are the
first from Moravia, Slovakia and from Poland. The findings suggest that M. tibialis generally
pupates at the end of September and at the beginning of October in Central Europe. Parasitoid
adults emerged during April. Development threshold temperatures for 50% adult emergence
was 2 deg C, the corresponding thermal constants were 294.6-311.0 Celsius degree-days. M.
tibialis has probably two generations a year, the first one parasitizing an alternate host (Bokor,
Cagan, 1999). It is shown that, within Central Europe, parasitism of the by the tachinid
parasitoid, Lydella thompsoni increased from 0.47 to 1.49% in south-western Poland (51 deg
03'N), and to 4.31-21.95% in eastern Slovakia (48 deg 20'N). The synchrony between the
parasitoid L. thompsoni and its primary host, the ECB, was studied in Central Europe under
conditions where the host is univoltine, but the parasitoid is bivoltine. A cumulated total of
more than 400 LT was field-collected from overwintering ECB larvae. The parasitoid
hibernated as larva inside the host. Pupation started in the second half of the following March
and 50% of pupation was surpassed in the first half of April. The first parasitoid adults
emerged at the end of April and the majority at the beginning of May. Development threshold
temperatures for 50% pupation was determined to be 2.7 deg C, and for 50% adult emergence
5.0 deg C; the respective thermal constants were 178.8-179.8 and 237.7-251.8 Celsius degreedays. Emerged adults did not parasitize overwintered ECB larvae in spring, hence there must
be an alternate host for the first generation of L. thompsoni in areas of univoltine life cycle of
the ECB. Parasitization of the ECB larvae by L. thompsoni continued until the end of July.
The first parasitoid adults from this second generation emerged in the second half of August.
By the end of the season, nearly one-third of L. thompsoni adults had emerged. The rest of
this generation apparently overwintered in the larval stage (Cagan et al., 1999).
Metathion E 50 parathion-methyl], Decis 2.5 EC [deltamethrin] and Furadan 350 F
[carbofuran] were applied on different dates for the control of O.nubilalis on maize in
Slovakia. Spray applications of deltamethrin and carbofuran substantially reduced the
abundance of the pest, while parathion-methyl was less effective (Cagan, 1993 b). Field
studies were conducted in Slovakia during 1991-93 to determine the injuriousness of O.
nubilalis on maize and to study the efficacy of various control measures. There was a strong
and positive correlation between the amount of rainfall and the level of damage caused by O.
nubilalis. Pyrethroid insecticides gave the most effective level of control, with Bacillus
thuringiensis giving only partial control. Larvae of O. nubilalis were infected by spores of
Nosema pyrausta, and the entomogenous fungi Beauveria bassiana. Arthropod predators
comprised Coccinellidae, Chrysopidae, Anthocoridae and Araneidae. Numbers of predators
peaked ten days after a peak in the pest population. Parasitoids consisted of Ichneumonidae,
Braconidae and Tachinidae (Cagan et al., 1995).
The analysis of pheromone glands from individual females of O. nubilalis originating in south
Moravia and Slovakia showed that this population utilizes the Z pheromone system. The ratio
of (Z)- and (E)-11-tetradecenyl acetates was found in the range of 98.5:1.5–99.5:0.5. Field
experiments confirmed the identity of the local population as being predominantly of the Z
25
strain. Individuals responding to E and hybrid blends were also detected (Kalinová et al.,
1994). Pheromone traps with different blends of pheromone were tested in maize fields in
Slovakia and Austria during 1992-94. Four pheromone formulations were selected for use in
the survey (with 99 : 1, 97 : 3, 35 : 65, 3 : 97 ratios of Z to E of 11-tda). Males of O. nubilalis
at all locations were mostly attracted to the 97 : 3 Z:E blend. Usually only a few males were
found in pheromone traps with 99 : 1 Z:E, 35 : 65 Z:E, and 3 : 97 Z:E blend. Compared with
the other locations investigated, a higher percentage of the males in pheromone traps with
blends different from 97 : 3 Z:E was observed at the Schloβhof location in Austria. Male
maxima in pheromone traps occurred after the egg maxima. Extremely dry climatic conditions
in June and July 1994 negatively influenced the numbers of captured moths. In conclusion,
this study showed that flight peaks of O. nubilalis could not be determined with certainty by
using pheromone traps (Cagan et al., 1996). Cagan and Barabas (1996a) during 1987-1991,
monitored O. nubilalis in light traps at three locations in Slovakia. The first pyralids in the
light traps were found in the warmest region of Slovakia, usually at the beginning of June and
within the physiological threshold of maize cultivation in the second half of June. The average
peak of flight was recorded at all locations in the first half of July. In August, the second, less
significant peak of flight was observed at warm locations. The average sum of temperatures
above 10 deg C from January until the time of the maximum number of pyralids in the traps
was 517.6 deg C at the coldest location and 547.0 deg C at the warmest location. High
average daily temperatures positively influenced the flight of the pyralids and led to greater
numbers being captured in the light traps Cagan, Barabas, 1996a).
2.4. Occurence of Ostrinia nubilalis in Europe and USA
A new distribution map was provided for Ostrinia nubilalis. Attacks maize, millet, sorghum,
Indian hemp, hops, Artemisia. Information was given on the geographical distribution in
Europe - Austria, Belgium, Bulgaria, Cyprus, Czechoslovakia, Denmark, France, Germany,
Greece, Hungary, Irish Republic, Italy, Netherlands, Norway, Poland, Portugal, Romania,
Sardinia, Sicily, Spain, Sweden, Switzerland, Turkey, United Kingdom, Yugoslavia, USSR,
Georgian SSR, Moldavian SSR, Russian SFSR, Kabardino-Balkaria, Kirov, Krasnodar,
Stavropol, Ukrainian SSR, Africa, Algeria, Egypt, Libya, Morocco, Tunisia, Asia, Iran, Israel,
Lebanon, Syria. In North America - Canada, Alberta, Manitoba, New Brunswick,
Newfoundland, Nova Scotia, Ontario, Prince Edward Island, Quebec, Saskatchewan, USA,
Alabama, Colorado, Connecticut, Delaware, Georgia, Illinois, Indiana, Iowa, Kansas,
Kentucky, Louisiana, Maryland, Massachussetts, Michigan, Minnesota, Mississippi,
Missouri, Nebraska, New Hampshire, New Jersey, New York, North Carolina, North Dakota,
Ohio, Oklahoma, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee,
Vermont, Virginia, West Virginia, Wisconsin (CAB International, 1991). Within the
European Union, the O. nubilalis is one of the major lepidopteran pest of maize in France,
Austria, Germany, Italy, Spain, Greece and Portugal (Bartsch, Schuphan, 2000). The O.
nubilalis found in almost all areas of Europe and America, is an extremely important pest
from the economic point of view (Szoke et al., 2002). The O. nubilalis, colonized maize after
its introduction into Europe about 500 years ago and is now considered one of the main pests
of this crop (Bethenod et al., 2005). O. nubialis was brought from Europe to America with
shipments of hemp, millet or broom-maize coming from Italy and Hungary. The corn borer
has existed for a long time in Hungary, but as in other European countries, in certain years has
caused serious losses. Despite the fact that Hungary has been one of the most important
centers of O. nubilalis infestations, no reliable statistical data covering the whole territory of
the country have been collected. O. nubilalis damages were observed as early as 1871, 1875,
1881, 1884, 1886 (cit. Kotlán, undated) especially in the southeastern regions. In 1926-1928
26
was O. nubilalis occurred in in all parts of Hungary were maize was produced (Kotlán,
undated). Appearance of O. nubilalis in Hungary and the number of generations show a
varied patterns. In the north-western parts of the country the one generation – while in the
southern, south-eastern areas the two generation populations do damages in general.
According to Keszthelyi and Lengyel (2002) tets, there were two generation of O. nubilalis
observed in two localities Balatonmagyaród (Zala country) and Várda ( Somogy country)
Hungary. The results showed the presence of two generation of O. nubilalis in both places
(Keszthelyi, Lengyel, 2002). Flight phenology of O. nubilalis and the effects of abiotic factors
on light trapping were studied in Balatonmagyaród and Várda, Zala and Somogy counties in
Hungary. The results confirmed the occurrence of a bivoltine corn borer at both sites. At
Balatonmagyaród, the population density of the first generation was higher, while at Várda,
the population density of the second generation was higher. The meteorological factors had
significant effects on the trapping of adults of both sexes. The female ratio was significantly
associated with minimum, maximum and average temperatures, and amount of rainfall
(Keszthelyi, Marczali 2003). Studies on the second seasonal flight of O. nubilalis in Hungary
were conducted. A survey was conducted in 3 sites (Fadd, Kecel and Kiskunfélegyháza) in
southern and south-eastern Hungary by cutting infested stems of the non-harvested maize
crops of the previous year to evaluate the second flight peak. Larval stages were also analysed
using maize stems from the current season. The examinations were made in time for the
second flight peak between 6 and 8 August. Only dead larvae and pupae were found in stems
of the crops from the previous year. Examination of the current season stems confirmed the
development of the second generation of the pest. Results indicated that the corn borer
produced a real second generation in the south-eastern parts of Hungary (Keszthelyi, Marczali
2004). The flight dynamics of the O. nubilalis was studied. The trend of the flight curves was
investigated at 45 sites throughout Hungary during 1999, 2000 and 2001. The effects of
abiotic elements on the number of individuals caught by light traps were also studied. Due to
the mild spring and the hot rainy summer, the incidence of bivoltinism shifted northwards.
The peak of the one-peak flight curve was observed between 15 June and July during 1999,
2000 and 2001. The typically univoltine populations appeared in northwest Hungary, covering
the counties of Vas and Györ-Moson-Sopron. The bivoltine generations appeared in a much
larger area in southern Hungary. The meteorological factors had significant effects on the
number of individuals caught by the light traps. The number of trapped individuals was
significantly correlated with maximum (p=99.2%; r=0.472), minimum (p=99.8%; r=0.549)
and average (p=99.8%; r=0.534) temperatures; precipitation (p=95.7%; r=0.327); and air
humidity (p=97.3%; r=0.265) (Keszthelyi, 2006). O. nubilalis flight and ecotype spread
examinations were also made in Hungary with the help of catching results of 44 agricultural
Jermy light traps. Catching data were evaluated by simple mathematical proportional
numbers. Catching results originating from different points of the country were compared
using the Walter-Lieth climate diagram and Péczely's Hungarian climate districts. The latter
was used to reveal correlations of flight types and different climatic districts. The previously
published flight alteration tendency of ECB continued in 2004. Generation quotients also
proved this process. Average generation quotient of populations in southeastern Hungary was
6 and the top of the same rate in this district was 10.84. The earlier observed one peak flight
type was replaced by 2 peaks flight type in northwestern Hungary (average generation
quotient of this district: 2.5). The relative individual number per one day (1RIN) shows
regressive tendency from southeastern Hungary to northwestern Hungary (1RIN of 1.district:
6.99; 1RIN of 4.district: 4.69; and 1RIN of 10.district: 2.78), but unequivocal conclusions
cannot be drawn from these values for places of ecotypes. There is no unambiguous
connection between Péczely's Hungarian climate districts and spread of ECB flight types as
proved by the statistical examinations (Keszthelyi et al., 2006). Keszthelyi and Marczali
27
(2007) in later study in 2006 by processing data on light trap catches recorded in the
Hungarian Plant Protection Information System (NIR) and meteorological information
supplied by the plant protection and soil conservation county services. The experiment was
conducted to determine the characteristics of the pest flight after the humid seasons in 2004
and 2005. In 2006 there were two peaks in the flight of ECB in various parts of the country,
the peak, so conspicuous in the past few years in the second part of summer, was not
observed. However, the statistical analysis of flight peak quotients in the dry and humid years
did not confirm any significant changes in the peaks compared to each other (f=2.169,
p=0.147). The frequent rainfall in June and August of 2006 interrupted ECB flight, split it to
various peaks, even, shifted it (at Nagybajom). Statistical analyses confirmed again the
significant relation between the increase in temperature (r=0.569, p=0.000002) and rainfall
volume (r=0.274, p=0.034) and the higher number of trapped individuals. The enhancing
effect of the latter factor on flight intensity can be explained by the high relative humidity
caused by much rainfall (Keszthelyi, Marczali, 2007).Veres ate al., (2006) investigated if
territorial differences in the damage caused by Helicoverpa armigera and O. nubilialis on
maize could be explained by the differences in the landscape structure by using 2 available,
independent national databases. Higher agricultural utilization rate for and the increase of the
patch size correlated to a higher rate of infestation. On the other hand, a higher rate of
compensation areas and the increase of the fragmentation (relative edge density and shape
index) correlated to a lower rate of the damages at landscape level (Veres et al., 2006).
During several years of studying bionomy and strains of O. nubilalis in Slovenia by light traps
and visual examination of development stages on maize, Gomboc and Milevoj (undated) have
observed considerable differences in the time of its appearance and in the number of its
generations in Slovenia. In Nova Gorica (near the Italian border) two generations per year
were observed during a three-year study. The first one starts in the middle of May and lasts
till the beginning of July, while the second one starts in the end of July and lasts till
September (its maximum being in the beginning of August). O. nubilalis shows a very similar
bionomy in the southern part of Slovenia, where equally two generations develop each year.
In the central and eastern part of Slovenia O. nubilalis develops only one generation per year,
this being rather long, as moths appear unevenly from the end of May till August. In order to
determine if the number of generations depends on climatic conditions two populations of O.
nubilalis - one from Prekmurje (near Hungarian border) and one from Nova Gorica - were
observed under the same conditions in greenhouse with net cower on the Biotechnical faculty
in Ljubljana. During this one-year study of bionomy under natural conditions it was found out
that the population from Nova Gorica developed two generations per year also under
somewhat colder conditions, while the population from Prekmurje had only one generation
yearly. The bionomy of the population from Primorje coincided in time with the bionomy of
the same population in the natural habitat which is an even greater surprise. The up to now
two-year study of O. nubilalis strains with pheromone traps did not give satisfactory results.
In Bilje, where two generations develop each year, the E and Z strains are equally common, in
central Slovenia the E strain is more usual, while the Z strain is the only one found in the
eastern part of Slovenia along the Hungarian and Austrian border. The Z strain develops only
one generation under the conditions in Slovenia, the same is true for the E strain in the central
part of Slovenia. The results on the O. nubilalis strains in Slovenia are identical to those
obtained by researchers in the neighboring countries bordering with Slovenia (Gomboc,
Milevoj, undated). In 1995 and 1996 the attack of ECB on different corn hybrids was
analysed at different locations in Slovenia. The observations were performed twice a year
during the flowering period and immediately before harvesting. Differences were evident
between hybrids and locations. The frequency of the 1995 attack was greatest on the tassels,
28
on the upper parts of the plants, on the upper leaves, in the central part of the stem and on the
cobs. The first counting in 1996 showed the greatest attack frequency on the leaves and on the
upper part of the stem, while it was negligible on the tassels. The ECB has two generations in
the continental parts of Slovenia, while in the region of Primorje (warmer as nearer to the sea)
it has very probably 3 generations (Gomboc et al., 1996). Pajmon (1997) described the main
insect pests of maize in Slovenia as described, viz. O. nubilalis, Diabrotica virgifera, Delia
platura, Oscinella frit, Agriotes and Agrotis species, and aphids, notably Rhopalosiphum
maidis, Metopolophium dirhodum, Schizaphis graminum, Sitobion avenae and Aphis fabae
(Pajmon, 1997; Gomboc, 2003). Gomboc et al., (1999) studied the bionomy of the O.
nubilalis in Slovenia over several years by light traps and visual examination of development
on maize, revealed considerable differences in the time of its appearance and in the number of
generations. In Bilje near Nova Gorica, 2 generations per year were observed during a 3 year
study. A similar situation was observed in Kostanjevica on Krka. In the central and eastern
part of Slovenia, O. nubilalis had 1 generation per year, with butterflies appearing unevenly
from the end of May until August. In Ljubljana, Kamnik, Prekmurje, Radlje on Drava, Žalec
and Pacinje near Ptuj 1 generation per year was observed. To determine if the number of
generations depended on climatic conditions, 2 populations of ECB - one from Prekmurje
(Mala Polana) and one from Primorje (Bilje) - were observed under the same conditions in a
greenhouse. The population from Primorje developed 2 generations per year, while the
population from Prekmurje had only 1 generation. The generations of the Primorje population
were similar to the population in the natural habitat (Gomboc et al., 1999). O. nubilalis has
been known as a pest of maize in Goriška region, Slovenia. During 1996-1998, more intensive
studies of the pest were performed. Bionomics was monitored by light traps placed in maize
fields. Moths were caught from the beginning of May until the end of September. Moths
caught in the traps were counted daily. During 1996-1997, infestation on some hybrids of
different FAO groups was monitored. In the experiment, 3 hybrids of FAO groups 400, 500,
600 and 700 were observed. Before harvesting, 60 plants were chosen randomly and
examined. Damage on plants and ears, and the number of the caterpillars in maize stalks were
evaluated. The results revealed that the European corn borer has 2 generations per year in this
region, and the intensity of infestation highly depended on weather conditions. The extent of
damages or percentage of infestation varied among the hybrids and FAO groups, and with
pest population density (Calrevaris et al., 2003).
Corn is grown in Croatia on 400000 ha, 40% is in monocultures. Most of this production is on
private farms, with average grain yield of 3.74 t/ha. On commercial estates and cooperatives,
yields were higher, approximately 5.23 t/ha, carried out on 17.93% agricultural land. The O.
nubilalis, under these conditions, completed one or two generations per year, with varying
annual attack intensity. Average intensity of attack in the area of eastern Slavonia in the last
25 years (1971-96) was 37.08%. During the last ten years the intensity of attack was around
50% (Raspudic et al., 1999). According to Ivezic and Raspudic (1999), O. nubilalis is
presented every year, with no such a low intensity, their control is not implemented. Maize is
sown as a monoculture, at 40% of maizefields, which also has influence on spreading of O.
nubilalis. In the last ten years average attack of O. nubilalis was 51,5% (Ivezic, Raspudic,
1999). O. nubilalis is one of the major pests of maize in Croatia. The selection of OS maize
hybrids has been conducted for more than 120 years. Many valuable materials have been
developed, which are now cultivated in various areas in Croatia. The resistance of some OS
hybrids to this pest was evaluated in field trials conducted during 1999-2001 in two localities
(Osijek and Karanac). Five OS maize hybrids were evaluated: OSSK 247, OSSK 332, OSSK
444, OSSK 552 and OSSK 644. Maize stalks were dissected during harvest. The intensity of
attack of ECB, position and length of damage, and grain yield were evaluated. The average
29
intensity of attack caused by ECB was 34.2%. The lowest attack intensity was recorded in
2000 (average of 9.6%), whereas the greatest was recorded in 2001 (average of 60.9%). The
length of damage on maize stalk was lowest in 2000 when the average damage was 0.48 cm
per plant; in 2001, 5.46 cm per plant were damaged. In 1999, when infestation was 34.2%, the
length of damage on the stalk was 0.95 cm per plant. The greatest length of damage on
hybrids was recorded in 2001, when hybrid OSSK 444 had damage of 16.62 cm per plant
(13.54 cm per plant in OSSK 552 and 10.68 cm per plant in OSSK 644). The infestation
intensity was more than 90% in 2001. If infestation intensity was lower than 40%, the greatest
length of damage on maize stalk was, on average, 1.58 cm per plant. If the intensity of attack
was more than 50%, the average length of damage on maize stalk was 5.78 cm per plant.
Significant positive correlation was observed between the intensity of attack and length of
damage. Some of the hybrids showed tolerance of ECB (Raspudic et al., 2003). Experiments
were conducted on maize hybrids during 1998 and 1999 in Križevci, Osijek and Belje PIK
Karanac, Croatia, to determine the occurrence of the European corn borer Ostrinia nubilalis.
In 1998, the intensity of corn borer infestation at Belje PIK Karanac was approximately
37.92% while at Osijek it was 80.83%. In 1999, it varied between 37.08% at Osijek and
71.20% at Križevci. The estimated number of holes per plant in all the 3 localities in both
years was higher than the number of larvae. The length of damage per plant was between 0.38
and 18. 80 cm. There were significant differences in the intensity of damaging effects on
different localities while there were no significant difference concerning various hybrids
(Augustinovic et al., 2005). Barcic (2007) described the biology and ecology of the O.
nubilalis, including morphology, life cycle and damage caused to maize plants. In Croatia in
2003-04, infestation levels of 37-45% were observed, although levels up to 64% were
recorded in the Slavonia region. Measures for preventing infestation and for controlling the
pest are described in detail, including agrotechnical, mechanical, biological, biotechnical and
chemical methods (Barcic, 2007).
In Romania 1971-75, the population trends of O. nubilalis on maize were studied in the nine
maize-growing regions, using as a criterion the number of larvae/ha prior to harvest in
autumn; the ability of the pest to cause yield losses was also assessed. The results, details of
which are given in tables, indicate a definite tendency in most areas for populations to
increase from one year to the next, so that in the whole country the average population
increased from 14 000 to 40 900 larvae/ha during the study period; this is considered to be
related to ecological conditions favouring the pest. Over the whole period and in all areas, the
proportion of damaged maize plants averaged 44% and the larval density/plant averaged 1.1;
crop losses varied from 1.3 to 17.7% according to the area, and the yield losses expressed as
the weight of kernels destroyed by each larva that reached maturity varied from 14 to 57 g
(Paulian et al., 1976). The economic threshold for damage to maize by O. nubilalis was
determined to be 5-10 egg masses/plant (Barbulescu, 1988). Due to Mustea (1999), the main
pests of maize crop in Transylvania, Romania, are Elateridae, Oscinella frit, Rhopalosiphum
maidis and O. nubilalis. The average annual damage recorded by these pests range between
20 and 25%. In evaluating the yield losses, we have taken into consideration the frequency
and intensity of damage, specific to each species: e.g. elaterids cause damage up to 6%, O. frit
2.4%, R. maidis up to 78% in early genotypes, and O. nubilalis up to 14% (Mustea, 1999).
Rosca and Barbulescu (1999) presented results obtained in Romania during 1990-1997 in
field trials with pheromone formulations developed for O. nubilalis. There was a relatively
good enough formulation of Z and E sexual synthetic pheromone, this formulation was not so
efficient and specific. It is stated that in Romania Z pherotype is predominant all over the
country. Their results underlined that the second generation generally occurs in Romania at
the end of August or early in September and practically is devoid of significance, since it is
numerically low on one hand, and during this period maize crop being to maturate, on the
30
other hand. Estimates of O. nubilalis populations in different Romanian’s areas are difficult
(Rosca, Barbulescu, 1999). The attack of ECB frequency ranges from one area to another and
from one year to another, on an average from 13% in Dobrudja up to 70% in Transylvania.
The damage caused by pest attack are direct (grain destruction) and indirect (stalk lodging,
scab appearance, losses at mechanical harvesting). On average, the rearing of one larva causes
damage to 34 g grains. At a crop density of 50,000 plants/ha and an attack with an average
frequency of 1.0 larva/plant, the yield losses could be in the region of 1,700 kg grain/ha. At
the country level, O. nubilalis has only one generation per year while in the south of Romania
two generations per year are possible. The use of pheromone traps can serve as a warning and
prognosis method. The parasitism of larvae by Lydella thomsoni was observed to reach 17.2%
(Popov et al., 2003). Pests infesting maize grown near Jimbolia, Timis County, Romania,
under continuous cropping for 2 years were studied during 2002-05. Pest incidence was
evaluated at 10- to 15-day intervals from May to September. Pests belonging to 11 families
were detected. In 2002, Tanymecus dilaticollis, Aphis maidis [Rhopalosiphum maidis],
Agriotes sp. and Phyllotreta vittula appeared during the onset of maize cultivation. In June, a
Cicadidae species, and Diabrotica virgifera virgifera, Oulema melanopus and Ostrinia
nubilalis were observed. D. virgifera virgifera adults appeared last in the field (beginning of
September). The same trend was observed in 2003. In 2004, pest emergence was delayed
because of the low temperatures in April and May. With regard to the percentage of infested
plants, the most important pests were T. dilaticollis (47.0-59.5%), adults of D. virgifera
virgifera (34.6-40. 33%), Oulema melanopus (27.9-32.5%), Opatrum sabulosum (17.531.0%), O. nubilalis (18.87-24.62%) and Aphis maidis (16.6-7.13%). The climatic conditions
were unfavourable for the development of T. dilaticollis adults. Phyllotreta vittula, Agriotes
sp. and Cicadidae species had low impact on maize. D. virgifera virgifera larvae, which were
present from May (2002 and 2001) and June (2004) until the beginning of August, resulted in
stalk bending in 4.42-11.08% of the plants. O. nubilalis, D. virgifera virgifera and Oulema
melanopus caused damage at the silking and cob formation stages (Grozea et al., 2006).
Alfaro Moreno (1972) made a detailed studies on Sesamia nonagrioides (Lef.) and
O.nubilalis (Hb.) on maize in the plains of the Ebro in eastern Spain. It is stated that S. cretica
Led. has not yet been observed on maize in that part of Spain, though it occurs in southern
Andalusia, in Almeria and near Madrid. Characters are given for differentiating the adults and
larvae of S. nonagrioides and S. cretica. Both S. nonagrioides and O. nubilalis have two
complete generations a year in the Ebro plains, and S. nonagrioides has a partial third in years
with long hot summers. Adults of Sesamia generally appear about 3-4 weeks before those of
Ostrinia; peak numbers of adults of the overwintering generation of Sesamia were recorded
between late May and late June, according to the year, and peak numbers of the summer
generation between mid-August and late September. Though large numbers of Ostrinia adults
were attracted to light-traps, Sesamia adults were not (Alfaro Moreno, 1972). Further studies
were carried out in 1972-73 in the Guadiana Plain in the Province of Badojoz, Spain, on the
biology of O. nubilalis on maize. The occurrence of 3 generations a year was confirmed, the
peaks of adult flight occurring in late May, mid-July and late August or early September. The
sex ratio (males to females) was 1.09, and males were more abundant at the beginning of the
flight periods. Females ovipositing a considerable time before flowers were available showed
a preference for the tallest plants, but nearer or during the peak of flowering they selected the
least well developed plants. The peak periods of oviposition were 25 May-10 June, the second
half of July and 25 August-15 September. Larval survival was generally low. The
overwintered generation pupated between late March and late June. Some larvae of each
generation entered diapause, and by 20 August (when the day length was 13 h 30 min) 100%
of them did so. The most suitable sowing dates to keep damage by O. nubilalis to a minimum
appear to be between 5 April and 15 May for this area.It is suggested that if the sum of
31
effective temperatures (above 10 deg C) is calculated from 15 March it will be possible to
forecast in early August the numbers of larvae of the second generation that will pupate
(rather than enter diapause) and give rise to a third generation, which is the generation causing
the greatest damage (Arias, Alvez, 1975). Eizaguirre and Alabajes (1989) gave a original and
bibliographic data on arthropod pests of maize in north-eastern Spain (Catalonia and Aragon),
where maize is a major crop and growers are applying increasing amounts of insecticides and
acaricides. The most important maize pest were mentioned - borers (Sesamia nonagrioides
and O. nubilalis (Eizaguirre, Albajos, 1989). Population fluctuations of both species were
studied in northwest Spain through 1990-96. The abundance of both species varied greatly
between and within locations. Their attacks were very intense in 1995 and 1996, reaching
100% of damaged plants in two plots, 30-50% in a third one and 7% in a fourth plot. In
several plots and years more than one larvae per plant at harvest was found. The captures of
adult moths made with pheromone traps indicate the existence of two generations, the first
one flying in May and the second one in July-August. The larvae of first generation of both
species rarely attack maize, but by September, most plants have been colonized by S.
nonagrioides and, to a lesser degree, by O. nubilalis larvae (Cordero et al., 1998). The most
important insect pests on maize in Spain are the pink stem borer S. nonagrioides and O.
nubilalis. Parasitoid degree of control on stem borers and other maize pests in Spain is not
known. Monetti et al., (2003) in research evaluated the incidence and diversity of parasitoids
on maize stem horns in the province of Pontevedra (NW Spain) (Monetti et al., 2003).
Baseline susceptibility to the Cry1Ab toxin was determined for Spanish populations of S.
nonagrioides and O. nubilalis from larvae collected on non-transgenic maize in the most
important growing areas (Galicia, Ebro, Madrid, Andalucía, Badajoz and Albacete). Annual
monitoring of field populations of both species collected on Bt-maize in the same
geographical areas has not revealed changes in susceptibility after three years of Bt-maize
cultivation in Spain (De la Poza et al., 2001). Valesco et al., (2004; Valesco et al., 2007) also
has confirmed that mentioned pests are the main in Pontevedra, Spain. The relative
importance of these species is considered and it is suggested that S. nonagrioides is the most
important pest of maize in the coastal region, while O. nubilalis is more important in the
interior (Valesco et al., 2004; Valesco et al., 2007).
Gavioli (1982) reviewed on the morphology, biology and control of O. nubilalis infesting
maize, on the nature of the damage caused especially by the 2nd generation (Gavioli, 1982).
In Northeastern Italy O. nubilalis is usually present at high levels and regarded as a main
problem by most farmers. Therefore ECB population levels and behaviour have been studied
for many years. A summary of data collected from 1982 to 2001 was given by Furlan and
Girolami (2001). First generation damage was usually low while all the plants after the second
generation were injured by the larvae. The highest eggs parasitization rate (by Thricogramma
spp.) was observed in 1982: 33% while in other years ranged between 11 to 24%. The number
of larvae and tunnel per plant ranged from 0.5 (2000) to 2-3 in most of the other years. At the
highest one Lydella thompsoni pupae out of 5 plants was observed. The peak of eggs
presence usually occurred in the second ten days of August, about 15 days later from the peak
of moth presence and several days after the period when most of treatments in normal farms
had been done. Light traps only recorded conspicuous captures while the sex pheromone traps
gave no reliable data (no more than 10 moths per season). Many treatments only slightly
improved crop protection in comparison with one treatment in the appropriate period. Light
traps and observation of the eggs only gave reliable information about ECB population
development (Furlan, Girolami, 2001).
In Poland , from 1992 to 1996 the voltinism of O. nubilalis was investigated by Cagan et al.,
(2000). The results indicated that degree-days accumulation during the whole year is not
responsible for the development of the second generation of O. nubilalis in Poland. Average
32
July daily temperatures in 1994 were extremely high (24.5 °C). Such temperatures can allow a
small partial development of the second generation of O. nubilalis at a relatively cold location
like Wroclaw in poland with a standard annual mean temperature of 8.3 °C. Their
investigation in the region of Wroclaw showed that damage caused by O. nubilalis increased
during 1992-1996. In 1994 remants of pupae of the pest in maize plants were found (Cagan et
al., 2000). Observations carried out at the Mikulice Plant Breeding Station in Poland showed
that infestation of maize by larvae of O. nubilalis increased from 2.7% of plants in 1994 to
96% in 2002 (Lisowicz, 2003).
In the north part of distribution area (Belgorod Province) of O. nubilalis., where phytophagan
gives one generation per season. The obtained data indicate that the pest mortality owing to
entomophagous (primarily larval parasitoids Lydella thompsoni and Eriborus terebrans) was
slight (within 9-24%) therewith egg parasitism by Trichogramma evanescens was at a level 02%. Larval death caused by pathogenic microorganisms lay in a range 2-11%. Maize
harvesting led to 18% decrease of diapausing larval population in average between years.
Population dynamics of the insect for the most part depend on the process of egg realization
by females (73-95% mortality at K 0.57-1.34) and also on the lst-2nd instar larval capability
for plant survival (62-79% mortality at K 0.42-0.69). K-factor analysis allowed to draw the
following conclusion: time interval of mating and egg -laying by females can be considered
one of the main critical periods in phytophagan life cycle and female ability for egg
realization must be taken as key factor of the O. nubilalis population dynamics in this zone of
Russia(Chumakov,Sukhanov,1999).
The distribution of the O. nubilalis was described in detail in the Rhineland between Aachen
and Cologne since 2000. The distribution limit moved about 12 km northwards in 2001. The
assessment of O. nubilalis was continued in 2002 and 2003. In the first year of the study,
Gathmann, Rothmeier, (2005) observed again a northwards distribution up to 13 km. In 2003,
the distribution limit did not change between Aachen and Cologne probably caused through
extreme hot and dry weather conditions during summer. Additionally the distribution was also
observed in the Bergischen Hohen for the first time in 2002. There O. nubilalis spread
continuously north- and eastwards in 2003 (Gathmann, Rothmeier, 2005). In Germany, the Z
race of the O. nubilalis has recently been spreading northwards. The insect has been moving
into the southern Rhineland since about 1996. Its northern border was described in detail in
2000. Continued mapping in 2001 showed that the northern border had shifted again by up to
12 km. Preliminary estimations of the further spreading process are made in consideration of
the major migration factors(Schmitz et al., 2002). In France O. nubilalis feeding on maize,
mugwort (Artemisia vulgaris), and hop (Humulus lupulus) are genetically different in France
and referred to as host-plant races (Pelozuelo, 2004). O. nubilalis is also wide spread pest in
Spain where, approximately 22 000 hectares (5% of the total maize growing area) of
transgenic maize have been planted annually in Spain since 1998 (Farinós et al., 2004). The
European corn borer Ostrinia nubilalis is a well-known and investigated pest of maize and
sweet corn particularly in the southwest of Germany since a long time. Nevertheless, the pest
can still surprise scientists and farmers. The first occurrence of a bivoltine race of the
European corn borer in South Badenia in 2006 and 2007 is remarkable. The European corn
borer had to be controlled in the last year on an area of approx equal to 60000 ha in Germany.
An important antagonist of this pest is the parasitoid T. brassicae, which is already used for
over 30 years on a continuously rising acreage for the control of O. nubilalis. The biology of
the pest and its parasitoid are recapitulated particularly with regard to the biological control.
The flight activities of the European corn borer are supervised with light traps in Southwest
Germany. The data were inserted into a central database at the LTZ Augustenberg (former
state institute), office Stuttgart (at first in 2007). The data can be used by advisors and
farmers. They determine the optimal time for the introduction of T. brassicae and optimize the
33
application of insecticides. The annual randomized monitoring of the T. brassicae quantities
and partially also qualities by the LTZ Augustenberg for plant protection helped to supply the
farmers with good T. brassicae material. The efficiencies of the T. brassicae introduction
reach up to over 70%. With the insecticide STEWARD (active ingredient indoxacarb) similar
and partly better efficiencies can be obtained. With the necessity of controlling Diabrotica
virgifera virgifera with insecticides, problems for the use of T. brassicae can arise; this is
discussed. (Albert, Dannemann, 2008).
O. nubilalis is the most important pest of maize in Switzerland. It is currently controlled by
mass releases of T. brassicae, an egg parasitoid (Derron, Goy, 2006). Pests infesting maize
grown near Jimbolia, Timis County, Romania, under continuous cropping for 2 years were
studied during 2002-05. Pest incidence was evaluated at 10- to 15-day intervals from May to
September. In June, a Cicadidae species, and Diabrotica virgifera virgifera, Oulema
melanopus and O. nubilalis were observed (Grozea, 2006).
O. nubilalis was first recorded in the Federal State of Niedersachsen, Germany, in September
2006. The species was found in seven localities, six of which where in the south east of the
state. The three sites with the highest infestation rates (5% or more of the maize plants
affected) were close to the borders to the federal states of Thüringen and Hessen from where
the species is assumed to have spread into Niedersachsen. The other sites showed infestation
rates of 1%. One isolated occurrence was reported from the north of Niedersachsen close to
the North Sea coast in a maize cultivar trial. In the main maize growing areas in the centre and
north of Niedersachsen, the corn borer was not found (Krussel, 2007; Lenz 2007). O. nubilalis
occurrence was also described in Saxony (Germany) since 1995. (Politz et al., 2007). Until
2006, the infestation of all maize cultivations amounts to approx equal to 80%. During 2007
year, a second generation was detected for the first time in Saxony. It was proved in several
locations of the Leipzig region. Parasitism by Bracon brevicornis on the European corn borer
larvae was observed in Saxony in 2003 and 2006 (Politz et al., 2007). O. nubilalis occurrence
at an economic threshold level of 0.43 larvae per stem was confirmed by Freier et al., (2007).
Predicting the potential distribution of agricultural pests, both indigenous and introduced,
plays a key role in determining the impact of global change on agricultural, horticultural and
forestry ecosystems. Trnka et al., (2007) investigated changes in the climatic niche of one of
the most important agricultural pests O. nubilalis, using the multi-generational phenology
model ECAMON. The model enables us to predict the development of the ECB to estimate
the risk of its establishing a permanent population, and to give an indication of climate-related
stress factors affecting the species. The evaluation of ECAMON demonstrated that it provides
accurate predictions of the onset and duration of the key phenological stages over a broad
range of sites. It explains over 70% of the variation in the timing of key developmental stages
based only on daily weather data. ECAMON simulations correctly predicted the
presence/absence of the ECB over the study region during the 1961-1990 reference period. It
also helped to explain the sudden increase in the maize infestation over the territory of the
Czech Republic during the unusually warm period of 1991-2000. The ECAMON results
demonstrated that the effect of climate will be significant and complex. According to our
estimates, the extent of the climate niche will expand within the next 20-30 years to cover
almost the entire area suitable for agriculture by 2040-2075. The establishment of a bivoltine
population is not imminent within the next decade, but it is likely to take place during the
period of 2025-2050. The timing and extent of these changes will be affected not only by
changes in the means of key meteorological parameters, but also in their variability (Trnka et
al., 2007).
O. nubilalis probably arrived to North America during the early 1900s in broom corn
imported from Hungary and Italy for the manufacture of brooms. O. nubilalis was first found
34
in North America near Boston, Massachusetts in 1917, later in 1921, in areas bordering Lake
Erie. It spread gradually from southern Michigan and northern Ohio. By the end of 1938, it
had spread only as far west as the Wisconsin shore of Lake Michigan. During its early history
in the United States, O. nubilalis produced one generation per year. By the late 1930s, a twogeneration per year population appeared in the eastern and north central states. This twogeneration per year O. nubilalis spread rapidly and soon became dominant in the central
Maize Belt. It reached Illinois in 1939, Iowa in 1942, Nebraska in 1944, and South Dakota in
1946. Meanwhile, the single-generation O. nubilalis spread northward into northern
Minnesota, North Dakota, and the Canadian provinces of Quebec, Manitoba, and
Saskatchewan (VanDyk, 1996). Later, three- and four-generation per year populations of
European corn borer appeared in the south along the Atlantic Coast and southwestward in
Missouri, Arkansas, Kansas, Oklahoma, and the Gulf states. European corn borer, O.
nubilalis, now has spread as far west as the Rocky Mountains in both Canada and the United
States, and south to the Gulf Coast states. European corn borer is thought to have originated in
Europe, where it is widespread. It also occurs in northern Africa. The North American
European corn borer population is thought to have resulted from multiple introductions from
more than one area of Europe. Thus, there are at least two, and possibly more, strains present.
This species occurs infrequently in Florida (Capinera, 2000). In the most of North America,
O. nubilalis has two generations a year (Palmer et al., 1985; Mason et al., 1996). The first
flight usually occurs in mid-June and last 2-3 weeks, and the second flight occurs from midJuly for 4-5 weeks (Leahy, Andow, 1994). The number of generations varies from one to four,
with only one generation occurring in northern New England and Minnesota and in northern
areas of Canada, whereas three to four generations occur in Virginia and other southern
locations. In many areas generation number varies depending on weather, and there is
considerable adaptation for local climate conditions even within strains. O. nubilalis larvae
overwinters in the larval stage, with pupation and emergence of adults in early spring.
Diapause apparently is induced by exposure of last instar larvae to long days, but there also is
a genetic component. Moth flights and oviposition usually occur during June-July and
August-September in areas with one to two generations annually. In southern locations with
three generations, moth flights and oviposition typically occur in May, late June, and August.
In locations with four generations, adults are active in April, June, July, and AugustSeptember (Capinera, 2000).
2. 5. The sources of control
2.5.1. Agrotechnics
O. nubilalis larvae overwinter in corn stalk residue. Therefore, removing maize by harvesting
it for silage will kill a high percentage of the borers, perhaps as much as 80% (Cullen,
Wedberg, 2005). Destruction of stalks, the overwintering site of larvae, has been long
recognized as an important element of corn borer management (Capinera, 2000). Hagerman
(1997) recomended clean plowing in the fall which killed a large percentage of overwintering corn borers and it was once a recommended control practice. However, it has been
believed that the reduction in corn borers achieved by plowing is less important than the soil
conservation that could be achieved by reduced tillage. Chisel plowing can kill 30 - 40% of
the over-wintering larvae and chopping stalks before plowing can increase that to about 95%.
Cultural management on a field by field basis has relatively little impact on next year’s
population because moths can disperse to new fields in the spring. In the univoltine area,
chopping stalks has been shown to be effective as an area-wide management technique, as it
kills most corn borers and greatly reduces the number of eggs laid. In the bivoltine area, the
35
relationship between killing overwintering larvae and the size of the second generation is
poorly understood (Hagerman. 1997). Capinera (2000) realised that disking is not adequate;
plowing to a depth of 20 cm is necessary for destruction of larvae. Mowing of stalks close to
the soil surface eliminates greater than 75% of larvae, and is especially effective when
combined with plowing. Minimum tillage procedures, which leave considerable crop residue
on the surface, enhance borer survival. Early planted corn is taller and attractive to ovipositing
female moths, so late planting has been recommended, but this is useful mostly in areas with
only a single generation per year. If a second generation occurs, such late planted corn is
heavily damaged (Capinera, 2000). Flush samples were taken in borrow ditches in central
Iowa during the first (spring) flight of moths in 2003 and 2004 to determine if cropping
patterns and crop phenology influence moth distribution across the landscape. Significantly
more moths were present in ditches with an adjacent cornfield on at least one side of the road
than in those with no corn on either side. In contrast, effects of corn stubble from the previous
year's crop, tillage, and corn phenology were weak or not detectable. Evidence suggests that
some moths emerging from corn stubble may aggregate in adjacent grass but that they
redistribute themselves in the landscape within a short time. Thus, the presence or absence of
adjacent corn was the overwhelming factor affecting spatial distribution of first-flight ECB
moths among grassy roadside ditches (Sappington, 2005). Good weed control can help
minimize the number of corn borers in a field. Moths normally rest and mate in grassy areas
outside the corn field, but if a field is very weedy they may spend more time in that field
resulting in proportionately more egg laying. Early harvesting can also help reduce harvest
yield loss due to corn borer. The longer a crop stands in the fall and the more wind it is
exposed to, the greater the potential for lodging, especially where corn borer populations are
high (Hagerman, 1997). Proper planting date is important for maize production. Therefore,
field studies were conducted from 1995-2005 to determine the most suitable planting date for
six maize hybrids (FAO 300-700 maturity groups) as influenced by infestation level of ECB.
Significant differences in the levels of ECB, level of damage and grain yield were observed
between the planting dates, and the years. The total plant infestation by both generations ECB
over the planting dates ranged from 47% to 60%. Plant damage rating was on the average of
2.2 and slightly differed across the planting dates. Yield results indicated that the planting
period for maize production in the Vojvodina province was from April 15 to May 5, but the
most suitable date was the beginning of the third week of April (Baca et al., 2008). The
effects of tillage, sowing date and fertilizer treatments on the infestation of maize hybrids by
O. nubilalis were studied in Pardubice, Czech Republic, during 2001-03. Maize
monocropping increased damage in plants due to O. nubilalis infestation by 37.0% in 2001,
44.0% in 2002, and 66.0% in 2003. The time of sowing had significant effects on the
population density of O. nubilalis. The first and second dates of sowing increased the pest
population by 15.3 and 53.9%, respectively. Only maize cobs were harvested and high
amounts of postharvest residues remained in the field, which served as reservoirs for the next
season. The tillage and fertilizer treatments had no significant effect on O. nubilalis incidence
(Stepanek et al., 2008).
2.5.2. Possibilities of Chemical control and biological solution (treatment)
Another source of controling O. nubilalis can be the effective use of insecticides or
bioinsecticides. Liquid formulations of insecticide are commonly applied to protect against
damage to corn, particularly from the period of early tassel formation until the corn silks are
dry. Recommendations vary from a single application prior to silking, to weekly applications.
Liquid applications are usually made to coincide with egg hatch in an effort to prevent
infestation. If corn borers are present in a field, however, the critical treatment time is just
36
before the tassels emerge, or at tassel emergence from the whorl. This plant growth period is
significant because the larvae are active at this time and more likely to contact insecticide
(Capinera, 2000). Control of O. nubilalis is a problem due to its prolonged presence in maize
fields, staggered ovipositing and the rapid entry of the larvae into the plant (Blandino et al.,
2006). Insecticide is more persistent when applied in a granular formulation. In grain maize,
insecticide applications for suppression of second generation maize borers can be made
outside the corn fields in areas of thick grass, or action sites, where adults tend to aggregate.
This approach has not been assessed for sweet maize. For borer suppression on potato, a
single application of insecticide timed to coinide with the presence of first instar larvae
provides optimal yield (Capinera, 2000). Alfaro Moreno (1972) in kis study mentioned that it
is generally too costly to apply treatments more than once to the crop, but an early application
of granules can afford valuable reductions in populations and increases in yields. The old
stalks should be burnt or completely destroyed mechanically, preferably before the beginning
of winter, to prevent the overwintering larvae reaching the underground parts of the plants,
where they will survive even though the stalks may be burnt (Alfaro Moreno, 1972). The
effects of soil insecticides (systemic and non systemic), alone or combined with insecticidal
sprays of above ground parts, on O. nubilalis and Sesamia nonagrioides in maize were
studied in field trials in North Spain. Soil granular insecticides, applied at sowing were
lindane (2%, 23 kg/ha), ethyl chlorpyrifos [chlorpyrifos] (5%, 24 kg/ha), phorate (5%, 14
kg/ha), and carbofuran (5%, 34 kg/ha). Chlorpyrifos 48% (200 cc/hl) was applied 1 week after
the peak populations of the 1st and/or 2nd generation of O. nubilalis. At harvest, numbers of
each borer species, galleries produced, numbers of fallen plants and maize yield were
evaluated. There was no interaction between soil and above ground treatments. No significant
differences in any of the parameters were observed among soil insecticides and untreated
controls. The best borer control was achieved with above ground sprays applied at least
during the 2nd generation of the pests. Counts of borers in untreated controls and spray
treatments applied during the 1st generations of the pests were similar (Felip et al., 1987). In
Romania, the effectiveness of granules of 8 insecticides, each applied at 2 kg a.i./ha, was
tested on maize plants artificially infested with O. nubilalis at higher rates than those likely to
occur in nature. The best results, in terms of stalk cavity length, number of larvae per plant,
percentage of plants with cob damage, and grain yield, were afforded by diazinon,
chlormephos, chlorpyrifos, carbofuran and profenofos (Voinescu, Barbulescu, 1986). One of
the first test based on new insecticides in Czechoslovakia were conducted by Longauerová
(1989). No chemical control had been used in the past because only Thiodan 35 EC
(endosulphan), an especially toxic compound, was registrated. Since the control against O.
nubilalis in Czechoslovakia is by aerial spraying, this preparation could not be used. In 1984
started experiments with different chemical and biological preparations, when new chemicals
were registrated: the synthetic pyrethroids, Decis 2.5 EC, (deltamothrin) 0.5l/ha, Cymbush 10
EC (cypermethrin) 0.5l/ha, Karate 5 EC (lambdacyhalothrin) 0.25l/ha, Vaztak 10 EC
(alphacypermethrin) 0.3l/ha and biological preparations such as, Bathurin 82 (Bacillus
thuringiensis) and Boverol Spofa (Beauveria bassiana) (Deuteromycotina: Hyphomycete),
were tested. In the year 1986 after tests the best results gets Vaztak and in the year 1987 Decis
(Longauerová, 1989). Rinkleff et al., (1995) conducted field and laboratory studies using
selected carbamate, organophosphate, and pyrethroid insecticides to quatify their toxicity to
O. nubilalis, egg and residual mortality to neonates. Field studies included the most
insecticides currently registered for O. nubilalis on vegetable crops, as well as recently
developed pyrethroids. Insecticides with the greatest ovicidial activity in field trials, in
decreasing order, included methomyl, encapsulated methyl parathion, permthrin, thiocarb,
zetacypermethrin, and lambda-cyhalothrin. With the exeption of methomyl, significant larval
mortality was also observed for each material. Of all materials tested, only methomyl
37
previously was assumed to have ovicidal activity on O. nubilalis. Laboratory bioassays were
conducted to estimate the LC50 for insecticides showing the greatest ovicidal activity in the
field. Insecticides with the greatest ovocidial activity included, in decreasing order, zetacypermethrin, lambdacyhalothrin, permethrin, methyl parathion, esfenvalerate, and methomyl.
With the exception of methomyl, all insecticides demonstrated high levels of residual toxicity
to neonates. Ovicidal activity of methomyl in the field had low inherent toxicity to eggs in the
laboratory bioassaywas partially explained by the use of a higher field rate relative to the
pyrethroids. Results in the field trials showed that all insecticides tested at curretly
recommended field rates have significant ovicidal activity on O. nubilalis. All insecticides,
with the exeption of methomyl, also caused significant neonate mortality. Ovicidal effects of
methomyl and methyl parathion were consistent in both field tests. Relative to the carbamates
and organophophates, the pyrethroids showed more moderate ovicidal activity (Rinkleff et al.,
1995). Another field studies were conducted in Slovakia during 1991-1993 to determine the
injuriousness of O. nubilalis on maize and to study the efficacy of various control measures.
There was a strong and positive correlation between the amount of rainfall and the level of
damage caused by O. nubilalis. Pyrethroid insecticides gave the most effective level of
control, with Bacillus thuringiensis gave only partial control. (Cagáň et al., 1995). In later
tests the most efficient insecticides were pyrethroids Karate –2.5 EC and Decis –2.5 –EC. A
similar result was achieved with preparation Consult – 100 –EC (hexaflumuron) in 1993 and
1994. Bacillus thuringiensis formulations were as efficient as pyrethroids in 1993 and 1994,
and not efficient enough in 1995. Time of aplication influenced the effectiveness of spraying
with Bacillus thuriengiensis preparations. The mortality of the European corn borer larvae
was very low when preparation Boverol (containing Beauveria bassiana spores) was used in
experiments. The best time for the corn borer control was 10 – 14 days after the beginning of
egg laying when the first damage leaves was found on maize plants (Tancík, Cagáň, 1998).
According to Pastorek (1999) in Slovakia, the most suitable time for chemical aplication
(Decis, Karate, Vaztak) is time when the larvae hatch (Pastorek, 1999). Krásnohorská (1999)
showed the registrated chemical solution in Slovak Republic: Decis EW 50 (0.25l/ha), Decis
25 Flow (0.5l/ha), Karate 2.5 EC (0.5l/ha), Nomolt 15 SC (1l/ha), Vaztak 10 EC (0.3l/ha),
Vaztak 10 SC (0.3l/ha) (Krásnohorská, 1999). Methodical book of Alchem company (2000),
chemical aplication of solution Vaztak 10SC/EC (0.3l/ha) and Decis EW 50 (deltamethrin
50g/l) (0.25l/ha) is two days after the maximum flying of adult moths to pheromone traps –
first half of July Alchem company, 2000). Bayer Crop Science in their methodical book for
plant protection (2003) recomended chemical aplication of solution of Decis EW 50
(deltamethrin 50g/l) one week after the maximum flying of adult moths to light traps (Bayer
Crop Science, 2003). Control of this pest was not implemented regularly in Croatia, and
sometimes even the basic agricultural practices were omitted (leaving maize in the field,
delaying plugging etc.) and the pest was allowed to remain over the winter, resulting in an
even more intensive attack the following year. Control of ECB was carried out on silage
maize with biological preparation Biobit XL (based on Bacillus thuringiensis) at a dose of 3
litres/ha. Intensity of attack was lower for 41%. The number of tunnels and larvae per maize
plant also decreased. On treated plots 0.64 tunnels and 0.67 larvae were found per one plant,
whereas on the control plots there were 1.61 tunnels and 1.79 larvae per plant. Both tunnels
and larvae were above the ear, because these were the larvae of the second generation. Length
of damage of maize stems in the control plots was 4.11 cm, and on treated plots 1.28 cm per
plant (Raspudic et al., 1999). Ostojcic et al., (2001) tested eight treatments applied to two corn
inbreds (Bc 492, Bc 592) at two location (Kopanica, Berava) in Croatia in 1994 and 1995.
Treatments were 3 systemic organophosphates (Lebaycid, Rogor, and Ekatin 25 EC), 2
pyrethroids (Sherpa and Karate), two formulations of Bacillus thuringiensis Berlinier (Biobit
XL; WP and FC), and 1 untreated control. Insecticide treatments were applied when at least
38
2/3 of the plants contained egg masses and at least 1/3 of the plants showed symptoms of
injury (shot-holing) in the whorl. Efficacy of the insecticide treatments was evaluated just
before harvest by dissecting 50 plants/treatment and counting the number of tunnels, number
of live larvae, measuring tunnel length, and grain yield. In 1994, 87% of the plants in the
untreated control plots were infested with O. nubilalis. The organophosphate treatments
reduced the infestation level by 42%, the pyrethroids by 40%, and the Bt treatments by 42%,
compared to untreated control. In 1995, 70% of the plants in the untreated control plots were
infested with ECB. The organophosphate treatments reduced the infestation level by 32%, the
pyrethroids by 30%, and the Bt treatments by 29%, compared to untreated control. In both
years, the organophosphate treatments provided the greatest yield protection from O.
nubilalis. Yields in these treatments were 13-19 % greater than the untreated control (Ostojcic
et al., 2001). Temperature often has a significant effect on the afficacy of insecticides used in
field. These temperature-depent differences may be due to changes in coverage, insect
behavior or insecticide toxicity. The most effective insecticide against a pest may vary with
environmental conditions.These results were confirmed in Muser and Shelton (2004) tests. In
laboratory assays was evaluated the influence of post-treatment temperature on the toxicities
of two pyrethroids (lambda-cyhalotrin and bifenthrin) a carbamate (methomyl) and a spinosyn
(spinosad) to O. nubilalis larvae. From 24 to 35 °C, the toxicities of the pyrethroids decreased
9.5- and 13.6 fold while spinosad toxicity decreased 3.8- fold (Musser, Shelton, 2004).
Impact of 3 control methods on larval O. nubilalis dynamics on maize was evaluated under
field conditions at Versailles in France. Labatte et al., (1996) studied insecticide based on
Beauveria bassiana and a transgenic maize hybrid. The experimental study showed that B.
bassiana control was similar to chemical control. The transgenic hybrid control was always
very high throughout the maize cycle studied. A substantial decrease of B. bassiana and
chemical control efficacy was observed with an increase in the delay between treatment and
infestation. The complementary studies of B. bassiana persistence, control impact, and
pathogen contact showed control-larval behavior interactions, which could explain this
decrease in efficacy. To take into account the main factors that condition control efficacy, a
modular and mechanistic model was proposed to describe larval dynamic and control impact.
The proposed control model made it possible to integrate O. nubilalis dynamics, and thus to
describe the time response of control (Labatte et al., 1996). Plant phenology also affects
chemically mediated oviposition response. The potential use of plant chemicals for
management of O. nubilalis in the field was suggested by (Udayagiri, Mason 1995). Exept the
maize plants, treatment is important in dense grasses bordering maize fields with carbaryl
which significantly reduced corn borer eggs laying within the maize field (Showers et al.,
1980). Oviposition deterrent activity of a natural enemy food supplement, Envirofeast (R),
against O. nubilalis females was studied in choice and no-choice tests under laboratory
conditions by Mensah et al., (2000). Maize plants treated with Envirofeast (R) at 25-40 g a.i./l
had significantly fewer egg masses per leaf and eggs per egg mass laid on them compared
with the untreated control plants in both choice and no-choice tests. However, maize plants
treated with Envirofeast (R) concentrations of 10-20 g a.i./l did not significantly deter the
insect's oviposition. The optimum rate at which Envirofeast (R) could deter oviposition was
25 g a.i./l. Increasing the rate of Envirofeast (R) application from 25-40 g a.i./l did not
significantly increase its oviposition deterrent activity against O. nubilalis. However, reducing
the rate from 25 to 20 g a.i./l resulted in a significant reduction in the oviposition deterrent
activity of Envirofeast (R). The egg masses laid by O. nubilalis on Envirofeast (R) treated
plants were essentially (80%) located on the lower leaf surfaces in contrast to untreated
(control) plants where only 40-60% of the egg masses were deposited on the lower leaf
surfaces. The egg masses on the Envirofeast (R) -treated plants were found at sites which did
not receive sprays, indicating the importance of good spray coverage when the product is used
39
in the field. The study has demonstrated the oviposition deterrent activity of Envirofeast (R)
against O. nubilalis on maize and this indicated that Envirofeast (R) may have the potential to
be integrated into programmes to assist in the control of O. nubilalis on maize (Mensah et al.,
2000). Vegetable and mineral oil, B. bassiana (Balsamo) and B. thuringiensis subsp. kurstaki
Berliner were evaluated for control of O. nubilalis, H. zea and Spodoptera frugiperda
(Lepidoptera: Noctuidae) in sweet maize. Field experiments in Maine and Massachusetts
during 1993 and 1994 evaluated oils and pathogens singly or in combinations, using a single
application directly to the top of the silk channel, immediately after pollination. Mineral oil
alone provided equal (1993) or better (1994) control compared with maize oil. In both years,
mineral or maize oil plus B. thuringiensis resulted in 93-98% marketable ears, compared with
48-52% marketable ears in untreated plots. In three factorial experiments with B. bassiana, B.
thuringiensis and maize oil, B. bassiana at 5 x 10(7) conidia per ear provided little or no
control while B. thuringiensis and maize oil provided significant though not always consistent
control of all three species. The combination of B. thuringiensis and maize oil provided the
largest and most consistent reduction in numbers of larvae and feeding damage to ears
(Hazzard et al., 2003). Due to Lisowicz (2003) the most effective control was obtained in
2002 by applying Karate 025 EC [lambda-cyhalothrin] at 0.2 litre/ha on 17 June and again on
8 July (Lisowicz). Zolnierz and Hurlej (2005) conducted in 2003-04 study to estimate the
extent of corn infestation by the larvae of the O. nubilalis in Opole province, Poland. The
efficacy of Trichoplus (Trichogramma spp.) and insecticide Karate Zeon 050 CS (lambdacyhalothrin) in the larvae control was investigated. The infestation of corn plants by the ECB
was very variable in Opole province. In 2004, on average, more than 40% of the plants were
infested. In the first year, the biological product (Trichoplus) was almost as effective as
Karate Zeon. In the second year, at one of the sites, its efficacy was also very similar to the
chemical insecticide. At the second site, probably because of poor product quality,
Trichogramma spp. did not control the ECB larvae. At the same site, the efficacy of Karate
Zeon was the highest in the two years of the study (82.1%) (Zolnierz, Hurej, 2005). Single
spraying of plants with preparation containing λ-cyhalothrin (Karate Zeon 050 CS) was
conducted during 2003 in Poland, when the population of the pest was highest. The
insecticide reduced the percentage of plants damaged by the larvae by up to 70.4% and the
number of larvae feeding on plants by up to 80.8%. In 2004-05, the chemical treatment was
performed during the period of mass hatching of the larvae (the basic date for their control).
The aforementioned treatment reduced the percentage of plants damaged by the larvae by up
to 61.9 and 68. 4% in 2004 and 2005, respectively. The number of larvae feeding per plant
was also reduced by up to 86.2% in 2004 and 80.0% in 2005. This treatment increased the
grain yield by 1.02 (15.7%), 0.91 (10. 9%) and 0.78 t/ha (9.3%) in 2003, 2004 and 2005,
respectively (Beres, 2006). The present research was carried out to study the possibility of
replacing the conventional insecticides (Malathion as organophosphorus insecticide and
carbaryl as carbamate insecticide) with safety environmental compounds (spinosad as
bioinsecticide and chlorfluazuron as IGR compound) to control the two corn borers Sesamia
cretica Led. and O. nubilalis. The results obtained revealed that all treatments were
significantly reduced the infestation of S. cretica. In the early season carbaryl showed the
highest general mean of reduction recording 79.43% reduction in S. cretica infestation
followed by chlorfluazuron (70.97%), spinosad (60.65%) and malathion (29.41%), while in
the late summer season chlorfluazuron recorded the highest general mean of reduction gave
57.15% followed by spinosad and carbaryl they were recorded 50.31 and 45.45%, whereas
malathion gave the lowest effect 27.59% reduction. All treatments significantly reduced O.
nubilalis infestation damage as compared with control in the early and the late summer
seasons. The efficiency of the tested insecticides against O. nubilalis can be arranged
according to the mean of reduction percentage during both seasons in a descending order as
40
follows: Spinosad, chlorfluazuron, carbaryl and malathion they were 73.11, 71.78, 65.32 and
38.03%, respectively. The general mean of change with increase in grain yield of the tested
insecticides during both seasons were arranged in a descending order as follows: spinosad,
chlorfluazuron, carbaryl and malathion giving 98.94, 84.20, 70.23 and 40.40%, respectively.
So it can be replacing malathion and carbaryl as conventional insecticides with spinosad and
chlorfluazuron as safety environmental compounds for controlling the two corn borers S.
cretica and O. nubilalis in pest management strategies (El-Mageed, Elgohary, 2007). AlDabel et al., (2008) determined the effectiveness of nC24 and nC27 petroleum spray oils
(PSOs) to reduce oviposition of O. nubilalis and survival of O. nubilalis eggs and
Trichogramma brassicae adults. Under choice and no-choice tests, maize treated with 3, 5
and 10% (v/v) of both oils deter O. nubilalis oviposition on maize. The study also showed that
treatment of 1-3-day-old O. nubilalis eggs with 1 and 2% (v/v) nC24 oil caused 6% mortality
compared with 99.5% when treated with 3, 5 and 10% (v/v) oil. In contrast, treatment with 110% (v/v) nC27 oil caused 99% mortality. T. brassicae is a major parasitoid of O. nubilalis.
The mortality of T. brassicae 24 h after exposure to maize sprayed with 2% (v/v) nC24 and
nC27 oils was 8.3 and 12.7%, respectively. At 5% (v/v), the mortalities were 24.9 and 23.5%,
respectively. Therefore, application of 3% (v/v) PSO may deter O. nubilalis egg lay, egg
mortality and survival of T. brassicae on maize (Al-Dabel et al., 2008).
Dipel-resistant and -susceptible strains of O. nubilalis were evaluated by Li et al., (2005a) for
larval mortality and growth inhibition when fed diets containing individual B. thuringiensis
protoxins. Resistance ratios for four of the protoxins in Dipel (Cry1Aa, Cry1Ab, Cry1Ac, and
Cry2Aa) were 170-, 205-, 524-, and > 640-fold, respectively, considerably higher than the 47fold resistance to Dipel. The Dipel-resistant strain was 36-fold resistant to Cry1Ba, a protoxin
not present in Dipel. Another non-Dipel protoxin, Cry1Ca, did not cause significant mortality
for either resistant or susceptible larvae with doses as high as 1.0 mg/ml. In an evaluation of
larval growth inhibition, resistance to Cry1Aa, Cry1Ab, Cry1Ac, and Cry1Ba was significant
at concentrations of 0.054 and 0.162 microg/ml. However, growth inhibition with Cry2Aa
was not significant at either dosem(Li et al., 2005a). Li et al., (2005b) in previous studies
suggested that B. thuringiensis (Bt) resistance in a Dipel-resistant strain of O. nubilalis was
primarily due to reduced trypsin-like proteinase activity. In study, they demonstrated a 254fold resistance to Cry1Ab protoxin but only 12-fold to trypsin-activated Cry1Ab toxin in the
Dipel-resistant strain. Significantly higher resistance to Cry1Ab protoxin than to trypsinactivated Cry1Ab toxin further supports the hypothesis that reduced trypsin-like proteinase
activity leading to reduced activation of the Bt protoxin is a major resistance mechanism in
the Dipel-resistant strain. To understand the molecular basis of reduced proteinase activity,
three cDNAs, OnT2, OnT23, and OnT25, encoding full-length trypsin-like proteinases, were
sequenced in Bt-resistant and -susceptible O. nubilalis larvae. Although a number of
nucleotide differences were found in sequences from the Bt-resistant and -susceptible strains,
the differences were not consistent with reduced trypsin-like activity in the Bt-resistant strain.
However, the mRNA levels of OnT23 in the resistant strain were 2.7- and 3.8-fold lower than
those of the susceptible strain as determined by northern blotting and real-time quantitative
PCR, respectively. Thus, reduced trypsin-like activity may be attributed to reduced expression
of OnT23 in Bt-resistant O. nubilalis. Li et al., (2005b) study provided new insights into Bt
resistance management strategies, as resistance mediated by reduced Bt protoxin activation
would be ineffective if resistant insects ingest a fully activated form of Cry1Ab toxin, either
in spray formulations or transgenic Bt crops (Li et al., 2005b). Coates et al., (2006)
investigated midgut expressed alkaline serine proteases of Lepidoptera function in conversion
of B. thuringiensis (Bt) protoxin to active toxin, and reduced level of transcript T23 is
associated with O. nubilalis resistance to Dipel Bt formulations. Three groups of trypsin(OnT25, OnT23, and OnT3) and two chymotrypsin-like (OnC1 and OnC2) cDNAs were
41
isolated from O. nubilalis midgut tissue. Intraspecific groupings are based on cDNA
similarity and peptide phylogeny. Derived serine proteases showed a catalytic triad (His, Asp,
and Ser; except transcript OnT23a), three substrate specificity-determining residues, and three
paired disulphide bonds. RT-PCR indicated all transcripts are expressed in the midgut.
Mendelian-inherited genomic markers for loci OnT23, OnT3 and OnC1 will be useful for
association of alleles with bioassayed Bt toxin resistance phenotypes (Coates et al., 2006).
Muresanu and Has (2006) presented results obtained during 1998-2002 regarding the efficacy
of biological (Trichogramma spp., biological products) and chemical (different insecticides)
treatments to reduce the O. nubilalis attack on maize genotypes released at Turda Agricultural
Research and Development Station. The biological treatments with Trichogramma maidis
significantly decreased the ECB attack and increased the yield between 4.0 and 18.8%. The
prerequisite to achieve high efficiency in the reduction of O. nubilalis attack, after the
treatments with Trichogramma spp., were: perform the releases at the best time and ensure the
density correspondingly to the pest density. The efficiency of the used products (with action
of eggs and larvae, Bacillus thuringiensis, lufenuron, fipronil, fenoxycarb, thiamethoxam,
cypermethrin+chlorpyrifos) was between 60 and 90% and the yield increases was between 8
and 12%. The utilization of the biological means and adequate crop management methods
contributes to the reduction of environmental pollution and the protection from pests
(Muresanu, Has, 2006). Biological control trials started in the 1980s using Trichogramma.
Today, one quarter of the maize area in Rheinland-Pfalz, Germany is treated with
Trichogramma, grain maize on average twice and forage maize once. To encourage use of
biological control which is more expensive than pesticide use, the Trichogramma usage has
been financially supported by the federal state's ministry for agriculture since 1983. Initial
payments of 60 DM/ha were reduced to 40 DM/ha in 1993 when the Corn borer became more
common and prices for Trichogramma decreased. Since 1999, due to EU notification
requirements and increased paperwork, many farmers stopped claiming the support. Since
2006, the programme for agriculture, environment and farming (PAULa) covers biological
control as a separate measure, however, rates of uptake by farmers are not yet known. There
have also been trials with Bacillus thuringiensis, however, the application requires specialised
mechanisation and the effectiveness was not very good, and therefore this methodology was
discontinued (Burghause, 2007). ECB´s had to be controlled in the last year on an area of
approx equal to 60000 ha in Germany. An important antagonist of this pest is the parasitoid T.
brassicae, which is already used for over 30 years on a continuously rising acreage for the
control of O. nubilalis. The efficiencies of the T. brassicae introduction reach up to over 70%.
With the insecticide STEWARD (active ingredient indoxacarb) similar and partly better
efficiencies can be obtained. With the necessity of controlling Diabrotica virgifera virgifera
with insecticides, problems for the use of T. brassicae can arise; this is discussed. (Albert et
al., 2008). Changes in the number of natural populations of Trichogramma, with possible high
levels of occurrences, such as those of T. evanescens, are considered. It is stated that the level
of infestation of eggs of the O. nubilalis by T. evanescens reached 97% in 1999 in Turkey.
Evidence also exists that natural control of the maize moth eggs in Europe by Trichogramma
usually does not exceed 25%. Investigations were conducted in Russia during 1994-2006 to
study the level of population of the maize moth on maize crops in the eastern part of the
Krasnodar region, south Russia. Correlation was found between the number of Trichogramma
populations and available feed resources or maize moth eggs (Serapionov, Frolov, 2008).
42
2.5.3. Sources of control with “Bt corn ”
Extensive breeding research has been conducted, and resistance has been incorporated into
grain maize, especially against corn borer populations with only a single annual generation. A
principal factor in seedling resistance to young larvae is a chemical known as DIMBOA,
which functions as a repellent and feeding detergent. It has proven difficult to incorporate the
known resistance factors into sweet maize without degradation of quality (Capinera, 2000).
Bacillus thuringiens - “Bt” is a naturally-occurring soilborne bacterium that is found
worldwide. A unique feature of this bacterium is its production of crystal-like proteins that
selectively kill specific groups of insects. These crystal proteins (Cry proteins) are insect
stomach poisons that must be eaten to kill the insect. Once eaten, an insect’s own digestive
enzymes activate the toxic form of the protein. The Cry proteins bind to specific "receptors"
on the intestinal lining and rupture the cells. Insects stop feeding within two hours of a first
bite and, if enough toxin is eaten, die within two or three days. For more than 30 years,
various liquid and granular formulations of Bt have been used successfully against ECB and
other insect pests on a variety of crops. There are several strains of Bt, each with differing Cry
proteins. Scientists have identified more than 60 Cry proteins. Proteins have been found with
insecticidal activity against the Colorado potato beetle (for example, Cry3A, Cry3C), corn
earworm (Cry1Ac, Cry1Ab), tobacco budworm (Cry1Ab) and O. nubilalis (Cry1Ab, Cry1Ac,
Cry9C). Most of the Bt maize hybrids, targeted against O. nubilalis, produce only the Cry1Ab
protein; a few produce the Cry1Ac protein or the Cry9C protein. Although conventional Bt
insecticides may perform as well as synthetic insecticides, their performance is not always
consistent. Erratic performance of Bt insecticides is attributed to: 1) toxin sensitivity to UV
radiation, heat and desiccation, 2) incomplete coverage of feeding sites, or 3) reduced toxicity
against older larvae. Modifying a maize plant to produce its own Bt protein overcomes these
liabilities. The protein is protected from rapid environmental degradation. Plants produce the
protein in tissues where larvae feed, so coverage is not an issue. Finally, the protein is present
whenever newly-hatched larvae try to feed, so the timing of Bt application is not a problem.
The result is an efficient and consistent built-in system to deliver Bt proteins to the target pest.
Plant geneticists create Bt maize by inserting selected exotic DNA into the corn plant's own
DNA. DNA is the genetic material that controls expression of a plant's or animal's traits. Seed
companies select elite hybrids for the Bt transformation in order to retain important
agronomic qualities for yield, harvestability and disease resistance. Three primary
components of the genetic package inserted into maize include: 1) Protein gene: Bt genes,
modified for improved expression in corn, produce Cry proteins. Initial Bt hybrids in the
United States and Canada include one of three Cry proteins, Cry1Ab, Cry1Ac or Cry9C.
Future hybrids may produce other Cry proteins, or proteins from other sources. 2) Promoter:
A promoter controls where and how much of the Cry protein a plant produces. Some
promoters limit protein production to specific parts of the plant (for example, leaves, green
tissue and pollen) whereas others produce protein throughout the plant. 3) Genetic marker:
The presence of a genetic marker allows seed companies to identify successful
transformations. Current examples of markers include genes for herbicide resistance or
antibiotic resistance. This genetic package is inserted into corn through a variety of plant
transformation techniques. Successful transformations, called "events," vary in the
components of the genetic package and where this DNA is inserted into the corn DNA. The
insertion site may affect Bt protein production and could affect other plant functions.
Consequently, seed companies carefully scrutinize transformation events to ensure adequate
production of Bt protein and no negative effects on agronomic traits (Witkowski et al., 2002).
Transgenic Bacillus thuringiens (Bt) toxin expressing maize (Zea mays, Bt176 Novartis) was
deregulated EU wide in 1997 and is expected to be used after the still pending admission of
43
new cultivars. An additional Bt-corn cultivar (Z. mays, Mon 810 Monsanto) was
commercialised in 1998 (Bartsch, Schuphan, 2000).
Phenological relationships play role in resistance evolution. Onstad and Gould (1989)
simulated resulting in increased survival of O. nubilalis populations infesting transgenic
maize using a model of population dynamics and genetics. The relationship between O.
nubilalis hatching period and maize maturation varied greatly from site to site and year to
year. The peak of the hatching period in the late summer generation of O. nubilalis occurred
at or after the average midpoint of the dough stage of maize. The last larvae tended to hatch
after the dough stage had passed and after the midpoint of the dent stage. In simulations where
5% of a region was planted with nontransgenic maize in separate refuge plots and 95% was
planted with transgenic maize, complete loss of titre as a result of senescence produced
resistance at the 3% resistance-allele level after 5 - 42 years, which was less than the 83 years
predicted by the standard model for resistance development when the transgenic maize lost no
titre as a result of senescence. Onstad and Gould hypothesized that genetically engineered
toxins (from Bacillus thuringiensis) have often decrease in leaf and stem titre as crops reached
maturation. The insects feeding and surviving on a crop during its senescence may have
important consequences for the population genetics of the breakdown of host plant resistance
(Onstad, Gould, 1989). Simulated population dynamics and population genetics of O.
nubilalis, and damage of maize in a hypothetical region containing transgenic and
nontransgenic maize and no other crops was observed by Onstad and Guse (1999). Their
model assumed that the same level of refuge for resistance management is used every year
over 15-20 yr and that no corn borers immigrate into the region over the same period. When
complete mixing across blocks between generations was assumed, the transgenic block
significantly lowers damage to maize in the refuges. For most scenarios without toxin-titer
decline during maize senescence, a 20% refuge is a robust, economical choice based on
current value. At extremes of initial pest density or crop value (price x expected yield), refuge
levels as low as 8% or as high as 26% can be superior. Nontransgenic maize could be planted
as strips (at least 6 rows per strip) within a field or as separate but adjacent blocks to be
effective at delaying resistance and providing economic returns at a 20% refuge level. With
toxin-titer decline during senescence, the model results were sensitive to several biological
parameters and assumptions with a 10% refuge level offering a robust, economic choice
(Onstad, Guse, 1999). Bourguet et al., (2000) simulated the strategies proposed for delaying
resistance to B. thuringiensis toxins expressed by transgenic maize require intense gene flow
between individuals that grew on transgenic and on normal (referred to as refuges) plants. To
investigate gene flow in the O. nubilalis, the genetic variability at 29 sampled sites from
France was studied by comparing allozyme frequencies at six polymorphic loci. Almost no
deviations and a high stability of allelic distribution was found among samples collected in
the same site over two or three different generations, indicating a high stability of the genetic
structure over time. The overall genetic differentiation was low at the region and whole
country level, suggesting a high and homogeneous gene flow (Bourguet et al., 2000). The
strategies proposed for delaying the development of resistance to the B. thuringiensis toxins
produced by transgenic maize require high levels of gene flow between individuals feeding on
transgenic and refuge plants. The O. nubilalis larvae may be found on several host plants,
which may act as natural refuges. The genetic variability of samples collected on sagebrush
(Artemisia sp.), hop (H. lupulus) and maize (Z. mays) in northern France was studied by
comparing the allozyme frequencies for six polymorphic loci. The authors found a high level
of gene flow within and between samples collected on the same host plant. The level of gene
flow between the sagebrush and hop insect samples appeared to be sufficiently high for these
populations to be considered a single genetic panmictic unit. Conversely, the samples
collected on maize were genetically different from those collected on sagebrush and hop.
44
Three of the six loci considered displayed greater between-host-plant than within-host-plant
differentiation in comparisons of the group of samples collected on sagebrush or hop with the
group of samples collected on maize. This indicates that either there is genetic isolation of the
insects feeding on maize or that there is host-plant divergent selection at these three loci or at
linked loci. These results had important implications for the potential sustainability of
transgenic insecticidal maize (Bourguet et.al., 2000). Rejase et al., (2000) was interested in
the workability of "refuge area" techniques aimed at preventing risks caused by the resistance
of corn borer to "Bt-maize". The study showed that there is a certain level of genetic
homogeneity between the populations collected on different maize plots. This suggested that
the corn borer has little difficulty migrating from one plot to another. Plots of non-genetically
modified maize could therefore become refuge areas so long as there is no significant lifecycle gap between resistant and sensitive borers (an issue which is yet to be resolved). There
was however evidence of genetic isolation in relation to corn borer species sampled from
maize, and also from hops or artemesia. It would therefore seem to be unwise to consider
using these two alternative host plants as natural refuge areas (Rejase et al., 2000). Davis and
Onstad (2000) were interested in dispersal of neonate of O. nubilalis, in seed mixtures of
transgenic maize expressing Cry1Ab protein (Bt+) and nontransgenic maize (Bt-) was
evaluated in a 2-yr field study. The main objective was to determine if larval dispersal limits
the effectiveness of seed mixtures as a resistance management strategy. Mixtures evaluated
included (1) all Bt+ plants, (2) every fifth plant Bt- with remaining plants Bt+, (3) every fifth
plant Bt+ with remaining plants Bt-, and (4) all Bt- plants. The transformation events MON
802 (B73 BC1F2 x Mo17) and MON 810 (B73 BC1F1 x Mo17), which express the Cry1Ab
endotoxin isolated from B. thuringiensis subsp. kurstaki, were used as the sources of Bt+ seed
in 1994 and 1995, respectively (Yield Gard, Monsanto, St. Louis, MO). At maize growth
stage V6-V8, subplots within each mixture (15-20 plants each) were infested so that every
fifth plant in mixtures 1 and 4, every Bt- plant in mixture 2, and every Bt+ plant in mixture 3
received two egg masses. Larval sampling over a 21-d period indicated increased neonate
dispersal off of Bt+ plants, reduced survival of larvae that dispersed from Bt+ plants to Btplants, and a low incidence of late-instar movement from Bt- plants to Bt+ plants. Computer
simulations based on mortality and dispersal estimates from this study indicated that seed
mixtures will delay the evolution of resistant O. nubilalis populations compared with uniform
planting of transgenic maize. However, resistant O. nubilalis populations likely will develop
faster in seed mixes compared with separate plantings of Bt and non-Bt maize (Davis, Onstad,
2000). The ability of non-crop plants to support complete development of insect pests is an
important factor for determining the impact of those plants on resistance management
programs for transgenic crops. Losey et al., (2002) assessed the effect of one physical factor,
plant stem diameter, on the ability of plants to support full development of the O. nubilalis,
the target pest of transgenic Bt-maize. In the field, O. nubilalis larvae were significantly more
likely to tunnel and survive in plants with larger stem diameters. Larvae were 40× more likely
to survive on maize, the largest plant tested, compared to many of the smaller plants. In the
laboratory, larvae were more likely to survive in and less likely to abandon the largest dietfilled artificial stems that varied only in stem diameter. In conditions simulating those that an
O. nubilalis larvae would encounter upon abandoning a host, larvae survived up to three
weeks and were able to locate maize as a new host with a significantly higher frequency than
would be expected if they were foraging randomly. These results indicated that the probability
of O. nubilalis larval survival to maturity on a plant other than maize was relatively low and
thus these smaller stemmed non-maize plants could not make a substantial contribution to the
pool of susceptible adults. Conversely, since more mature larvae were not as susceptible as
neonates, any larvae that partially developed on non-maize plants and subsequently colonize
Bt-maize could not be exposed to a lethal dose of the toxin. Since some proportion of the
45
individuals that survive could be partially resistant heterozygotes the presence of non-maize
host plants could facilitate the development of resistant O. nubilalis populations (Losey et al.,
2002). A 3-year, multi-state survey of farmers who had planted transgenic Bt maize was
conducted to evaluate perceptions of Bt maize performance and its utility as a management
option O. nubilalis. The states growing the highest percentage of Bt maize were Minnesota,
Iowa and Nebraska. However, Illinois was adopting Bt maize at the fastest rate. Historical use
of insecticides did not influence the adoption of Bt maize. In addition, of those farmers who
used insecticides to control European corn borer, the percentage that decreased their use of
insecticides nearly doubled from 13.2% (1996) to 26.0% (1998) over this 3-year period. The
primary reason farmers planted Bt maize was to eliminate the yield loss caused by ECB.
Scouting for ECB decreased from 91% (scouting 2.2 times a year) in 1996 to 75% (scouting
1.8 times a year) in 1998. The percentage of farmers not scouting for ECB increased from
9.6% (1996) to 25% (1998). Most farmers believed yields of Bt hybrids were either similar to
or greater than the yields of non-Bt hybrids. Minnesota farmers perceived the greatest yield
advantages. Farmers are becoming more aware of insect resistance management guidelines;
however, they also clearly show preferences for having the flexibility to use different spatial
plantings of Bt and non-Bt maize. Finally, after having planted Bt maize and obtained
excellent control of ECB, most farmers believed that this insect had been causing more yield
loss than they previously had suspected in their non-Bt maize (Pilcher et al., 2002). Pilcher
and Rice (2003) in later study again determined the utility in managing ECB. Transgenic Bt
(events 176 and Bt11) corn and non-Bt corn were planted at three different times to use the
early- and late-planted corn as a potential trap crop for ovipositing ECB moths. Grain
moisture and yields were recorded to determine the economic benefits of Bt corn planted on
the different dates, based on ECB populations and corn damage data collected before harvest.
Data were recorded from three locations in southwestern, central, and northeastern Iowa for
three summers (1996-1998). Economic benefits are discussed in relation to EILs and yield
results. Adjusting the planting dates of Bt and non-Bt corn provided variable economic
differences among planting dates in northern Iowa; however, greater economic benefits were
realized when Bt corn was planted late during the planting sequence in central and
southwestern Iowa. These results suggest that planting corn should be conducted in a timely
manner and, if delayed or required to plant late, planting Bt corn would likely provide greater
economic benefits. Although yield and economic variability were high, using Bt corn in
combination with planting date adjustments may be a viable option for managing ECB
(Pilcher, Rice, 2003). The phytophagous insects that damage crops are often polyphagous,
feeding on several types of crop and on weeds. The refuges constituted by noncrop host plants
may be useful in managing the evolution in pest species of resistance to the B. thuringiensis
toxins produced by transgenic crops. However, the benefits of these refuges may be limited
because host-plant diversity may drive genetic divergence and possibly even host-plantmediated sympatric speciation (Martel et al., 2003). The development of genetically modified
Bt-corn, incorporating various toxin genes from Bacillus thuringiensis that act as a chemical
defence against insect pests, such as the ECB, provides farmers with a new pest management
option. However, the emergence of insect resistance is a threat to the continued use of Btcorn. The United States Environment Protection Agency (US EPA) has developed planting
strategies, for preventing insect resistance by planting a mixture of Bt- and non-Bt-corn.
Decisions about the exact proportion of Bt- and non-Bt-corn are based on complex spatially
explicit mathematical models using detailed biological assumptions about the population
genetics and life history of the ECB. Linacre and Thompson (2004) developed an alternative
simpler model for the spread of resistance based on the logistic growth model, which was
believed to utility in situations where it is impossible or impractical to estimate the different
life history and genetics parameters required by more detailed models. The model to
46
investigate the US EPA's planting rules for Bt-corn was creating and found that short-term
economic behaviour is likely to lead to these rules not being followed. Bt-corn appears to be
economic in markets that do not differentiate and uneconomic in markets where consumers do
differentiate (Linacre, Thompson, 2004). Dillehay et al., (2004) in his study evaluated Bt
hybrids, their near isolines, and leading non-Bt hybrids for grain yield, moisture, and test
weight under natural infestations of ECB in 2000, 2001 and 2002 at four to six locations
across Pennsylvania and Maryland each year. Averaged over all locations and years, Bt,
isoline, and lead hybrids yielded 9.1, 8.6, and 8.5 Mg ha-1, respectively. Grain moisture
content at harvest was 224, 216, and 214 g kg-1 and test weight was 705, 713, and 713 kg m-3
for Bt, isoline, and lead hybrids, respectively. Overall, Bt hybrids produced higher yields, but
also had higher grain moisture content at harvest and lower test weight than isoline and lead
hybrids. Yield and moisture content differences were correlated with ECB infestations, but
test weight was not. Isoline and lead hybrid yields were reduced by 2.37 and 2.60%
respectively, for each ECB tunnel. Precipitation had no consistent effect on Bt and non-Bt
hybrid differences for yield, moisture, or test weight. Delayed planting dates were associated
with higher ECB infestations. This may be beneficial in predicting sites that could benefit
from Bt hybrids. In some environments in Pennsylvania and Maryland, Bt hybrids can result
in significant yield advantages (Dellehay et al., 2004). A faunistic study investigating the
potential side effects of maize genetically modified to express a truncated Cry1Ab protein
derived from B. thuringiensis subsp. kurstaki (Bt), on nontarget arthropods was carried out
under field conditions (Burgundy, France). The communities of nontarget arthropods in the
soil, on the leaves and flying in the crop area were monitored throughout the growing season.
Water-treated, untransformed maize served as a control, and a spray application of a bacterial
Bt insecticide (Delfin WG) and a synthetic insecticide (Karate Xpress) used to control the
ECB acted as positive reference treatments. Results were analysed using a principal response
curve. Significantly lower infestations by the lepidopteran target species O. nubilalis were
observed in the Bt-maize plots compared to the control. No effects of Bt-maize on the
communities of soil- and nontarget plant-dwelling arthropods were observed. A trend towards
a community effect on flying arthropods was observed with lower abundance of adult
Lepidoptera, flies in the families Lonchopteridae, Mycetophilidae and Syrphidae, and the
hymenopteran parasitoids Ceraphronidae. The effects were weak and restricted to two
sampling dates corresponding to anthesis. A short but statistically significant effect of Karate
Xpress and Delfin was observed on the community of plant dwellers and a prolonged effect of
Karate Xpress on the soil dwellers (Candolfi et al., 2004). Dubelman et al., (2005) tested the
persistence and accumulation of the Cry1Ab protein in soil as a result of sustained planting of
genetically modified Bt corn hybrids. Soil samples were collected from agricultural fields in
five corn-growing regions of the United States where Bt corn hybrids (MON 810 or Bt11) had
been planted for at least 3 consecutive yr. At each site, soil samples were collected during the
corn-growing period (postanthesis) and again within 6 wk after harvest. Multiple soil
specimens from matched Bt cornfields and nearby, non-Bt control fields were analysed by
diet-incorporation insect bioassay, using growth inhibition (GI) of the ECB as the toxicity
endpoint. Positive control soil samples containing Cry1Ab protein at the GI50 level (0.05
micro g/g soil) were analysed in tandem with test and control samples to verify that the
bioassay was able to detect low levels of Cry1Ab protein. The limit of detection for Cry1Ab
protein in soil was 0.03 micro g/g soil. The presence of Cry1Ab protein in soil was assessed
by statistical comparison of the insect toxicity (GI) of soils collected from Bt and non-Bt
(control) cornfields. Only one soil sample, collected postanthesis in a Bt cornfield that had
also been treated with carbofuran insecticide, showed insect toxicity. This toxicity was below
the GI50 level, and no toxicity was detected in the soil collected from the same plot shortly
after harvest. Therefore, there is no evidence of persistence or accumulation of Cry1Ab
47
protein in soils from fields planted for at least three consecutive growing seasons with Bt corn
hybrids (Dubelman et al., 2005). Alves et al., (2006) tested the offspring of various crosses to
determine the mode of inheritance of resistance to Cry1Ab. Patterns of inheritance of
resistance were similar in the two resistant strains. The progeny of reciprocal F1 crosses
(resistant male x susceptible female and vice versa) responded alike in bioassays, indicating
autosomal inheritance. The median lethal concentrations (LC50 values) of F1 were
intermediate between the resistant and susceptible parents, indicating approximately additive
inheritance. However, the dominance of resistance increased as the concentration of Cry1Ab
decreased. Analysis of progeny from backcrosses (F1 x susceptible strain) suggests that
resistance was controlled by more than one locus. In particular, the fit of observed to expected
mortality improved as the number of putative loci increased from 1 to 10. The polygenic
nature of resistance in these two laboratory strains suggests that major genes for resistance to
Cry1Ab were not common in the founding populations of ECB. A low initial frequency of
major genes for Cry1Ab resistance might be an important factor in delaying evolution of
resistance to Bt corn in this pest (Alves et al., 2006). The use of transgenic crops producing
toxins from the bacterium Bacillus thuringiensis - or Bt crops - is associated with the risk that
the targeted pests become resistant to these toxins. To reduce this risk, the US government
required the implementation of a strategy named High Dose/Refuge (HDR). This strategy is
based on maintaining Bt toxin-free plants or crops - referred to as "refuges" - to preserve a
pool of susceptible insects in the vicinity of Bt fields. Among other factors, its efficiency
relies on a high gene flow between these susceptible individuals and any resistant individuals
selected in Bt fields. For several pests targeted by these toxins, this strategy was nevertheless
implemented when little was in feet know, as to the life history traits likely to influence the
intensity of the gene flow. Part of this gap has been filled since then: we summarize here the
recent advances on the ECB, one of the main targets of insecticidal Bt maize. Although this
moth pest is highly polyphagous, its other host plants - whether wild or cultivated - do not
provide a sufficient source of susceptible individuals to efficiently prevent toxin resistance
from developing. Moreover, a fraction of the ECB reproduce in close vicinity of their place of
emergence, so that refuges situated a few hundred meters from Bt maize fields - the maximal
distance currently required is 800 meters - may not warrant a sufficient intermixing between
susceptible and resistant individuals. In crop rotation situations, this intermixing could
however be facilitated through a contrasted management of herbaceous maize field borders.
Although 10 years after the beginning of Bt maize cultivation no resistance has yet broken
out, our data suggests that it is illusory to aim at a universally suitable strategy, and that the
HDR strategy - as currently implemented - may not necessarily be optimal (Dalecky et al.,
2007).
Biogas plants fuelled with renewable sources of energy are a sustainable means for power
generation. In areas with high infestation levels with O. nubilalis it is likely that transgenic
Bt-maize will be fed into agricultural biogas plants. According to Rauschen and Schuphan
(2006) the fate of the entomotoxic protein Cry1Ab from MON810 maize was therefore
investigated in silage and biogas production-related materials in the utilization chains of two
farm-scale biogas plants. The Cry1Ab content in silage exhibited no clear-cut pattern of
decrease over the experimental time of 4 months. Mean content for silage was 1878 +/- 713
ng Cry1Ab g(-1). After fermentation in the biogas plants, the Cry1Ab content declined to
trace amounts of around 3.5 ng g(-1) in the effluents. The limit of detection of the employed
ELISA test corresponded to 0.75 ng Cry1Ab g(-1) sample material. Assays with larvae of O.
nubilalis showed no bioactivity of the reactor effluents. The utilization of this residual
material as fertilizer in agriculture is therefore deemed to be ecotoxicologically harmless
(Rauschen, Schuphan, 2006). Recent speculation of slower residue decomposition for Bt corn
hybrids compared with non-Bt corn hybrids has prompted investigative study. Lehman et al.,
48
(2008) evaluated the residue decomposition rates of Bt and non-Bt corn hybrids over a period
of 22 mo under field conditions using the litter bag technique. The four corn hybrids used
were (i) DKC60-16 (Bt+, Cry1Ab protein active against the lepidopteran European corn
borer, event MON810), (ii) DKC60-12 (Bt+, Cry3Bb1 protein active against the coleopteran
corn rootworm, event MON863), (iii) DKC60-14 (stacked Bt++, Cry1Ab and Cry3Bb1
proteins) and, (iv) DKC60-15 (Bt-, base genetics). The biochemical and physical properties of
the corn residues were determined. No differences in the decomposition rates of the residue
from the four corn hybrids were detected. Residue decomposition rate constants were
approximately 0.25 d-1 for all four hybrids with predicted residue half-lives of about 200 d.
No differences in compositional properties, including lignin content, were observed among
the four hybrids. Physical compression testing of the chopped residue failed to detect
significant differences in mechanical strength properties among the hybrids. This is the first
report regarding decomposition of Bt corn residue under field conditions following
ambiguous reports from laboratory studies on the relative susceptibility of Bt corn residue to
decomposition (Lehman et al., 2008).
2.5.3.1. Correlation between Bt corn and natural parasitoids of Ostrinia nubilalis
The application of transgenic crops has expanded enormously since their introduction to
agriculture in the 1990s. Despite increased research activity in the area of non-target effects,
the impact on many groups of soil organisms still remains unclear (Weber, Nentwing, 2006).
In a 1994 Orr and Landis (1997) in their field experiment in Michigan, tested oviposition,
predation, and parasitism of O. nubilalis in transgenic and isogenic maize. Plots of plants
expressing the Cry1A (b) protein of B. thuringiensis subsp. kurstaki and plots of isogenic
plants both had 2nd-generation O. nubilalis egg masses densities of 1.1/plant, indicated a lack
of antixenosis by transgenic plants. Distribution and size of egg masses on plants was also
unaffected by maize type. Size of plants was the same in both treatments. Levels of egg
masses predation were 24.75 and 19.35%, respectively, but not significantly different between
the transgenic and isogenic plots. Parasitism of egg masses was not significantly different
between transgenic and isogenic plots, and was low at 6.31 and 4.41%, respectively.
Percentage of eggs within masses which hatched was 10.2% lower in transgenic than in
isogenic plots. However, neither predation, parasitism, or sloughing of eggs from plants were
significantly different between the 2 treatments. Densities of O. nubilalis predators were not
different between the 2 treatments throughout the O. nubilalis oviposition period. Parasitism
of O. nubilalis larvae by E. terebrans and M. grandii was not significantly different between
plots and ranged from 2.4 to 7.0%. Although most differences between transgenic and
isogenic plants were non-significant, all observed differences in natural enemy population
parameters under the experimental conditions were in the direction opposite to that expected
if transgenic plants had an adverse impact (Orr, Landis, 1997). Bourguet et al., (2002)
evaluated in field trials the effects on non-target species, of transgenic maize producing the
Cry1Ab toxin of B. thuringiensis (Bt). In 1998, they collected O. nubilalis larvae from
transgenic Bt maize (Novartis Hybrid 176) and non-Bt maize at four geographical sites. They
found a significant variation in parasitism by the tachinids Lydella thompsoni and
Pseudoperichaeta nigrolineata among sites, and more parasitism in non-Bt than in Bt fields.
The Bt effect did not vary significantly among fields. In 1999, they performed a field
experiment at two sites, comparing the temporal abundance of non-target arthropods in Bt
maize (Monsanto Hybrid MON810) and non-Bt maize. The non-target insects studied
included the aphids Metopolophium dirhodum, Rhopalosiphum padi and Sitobion avenae, the
bug Orius insidiosus, the syrphid Syrphus corollae, the ladybird Coccinella septempunctata,
the lacewing Chrysoperla carnea, thrips and hymenopteran parasitoids. For all species but
49
one, the number of individuals varied greatly over the season but did not differ between the
types of maize. The only exception was thrips which, at one site, was significantly more
abundant in Bt maize than in non-Bt maize. However this difference did not remain
significant when the multiple tests were taken into account (Bourguet at al., 2002). Field trials
and laboratory bioassay were used to evaluate the effects of transgenic maize, on the nontarget species Lydella thompsoni Herting, parasitoid of O. nubilalis. In 1998 and 1999 the
larvae of O. nubilalis were collected from Bt maize and non Bt-maize at 9 geographical sites.
Considering the total larva amount, the ECB from transgenic maize showed lower parasitism
levels in terms of both percentage and absolute parasitoid number. In fact the statistical
analysis demonstrates that, over the two years, there was a difference in parasitism rate by L.
thompsoni in Bt maize versus the near isogenic non-Bt maize. However four localities had
higher parasitism percentages for Bt maize larvae. It was also shown that there was a
significant variation in the parasitism rate in the fields and field locations. There were no
significant differences in parasitism in the two years, and none of the interactions were
significant. The biology of L. thompsoni parasitizing ECB larvae from isogenic and transgenic
maize was investigated. The parasites emerging from borers reared on the two maize hybrids
showed no significant difference in lifespan or adult longevity. However as maize borer
populations decline in Bt corn and this study report a decline as well of the number of
parasitoid, refuge areas, may moderate these indirect effects and they should considered also
for conserving natural enemies (Manachiny, 2003). Manachiny and Lozzia (2004) in later
study aimed at a better understanding of the influence of transgenic maize on two parasitoids
of ECB. In order to detect the effects on parasitism rate by Lydella thompsoni on ECB, mature
larvae of O. nubilalis were collected from Bt maize (event 176) and from its isogenic line at
nine geographical sites. Considering the entire amount of the larvae, the ECB from transgenic
Bt maize displayed a lower level of parasitism both in percentage and in absolute numbers of
parasitoids. Trichogramma brassicae was the main egg parasitoid species of O. nubilalis
recorded in maize fields in Northern Italy. The levels of parasitism, the vitality of embryos
and adults and the sex ratio of T. brassicae were investigated. For this goal, egg masses of O.
nubilalis, collected from isogenic and transgenic maize fields were used. Statistical analyses
revealed no significant differences in the percentage of parasitism, number, longevity and
mortality of adults of T. brassicae emerging from ECB eggs oviposited on Bt or isogenic
maize leaves. No statistical differences were recorded for all parameters analysed for T.
brassicae emerging from eggs of ECB surviving on transgenic maize or collected from a
conventional maize crop (Manachiny, Lozzia, 2004). The species Trichogramma brassicae is
a naturally occurring enemy of the ECB. The effects of transgenic maize plant food sources
were tested on adults of T. brassicae. The experiments followed the principles of the
IOBC/WPRS testing guidelines with minor modifications. The following maize cultivars were
tested and compared in the laboratory: Pactol CB (Bt 176) and Novelis (Mon 810) and the
respective non-transformed cultivars Pactol and Nobilis. Groups of T. brassicae were exposed
to the different maize food sources into glass cages: pollen, honeydew from Sitobion avenae
aphids and phloem sap. The rate of parasitism of the ECB by T. brassicae was calculated as
eggs per female and comparisons were made between Bt, non-Bt food sources and control.
With pollen, the parasitism per female was 18.92 plus or minus 3.36 eggs for control, 22.56
plus or minus 2.24 eggs for Pactol CB (Bt 176), 18.62 plus or minus 2.27 eggs for Pactol
(non-Bt), 15.54 plus or minus 3.15 eggs for Novelis (Mon 810) and 24.53 plus or minus 1.93
eggs for Nobilis (non-Bt). When exposed to phloem sap from stem tissue, parasitism was
22.46 plus or minus 4.60 eggs for control, 16.98 plus or minus 5.82 for Pactol CB (Bt 176),
14.07 plus or minus 2.54 for Pactol (non-Bt), 14.92 plus or minus 4.08 for Novelis (Mon 810)
and 14.34 plus or minus 1.88 for Nobilis (non-Bt). The highest parasitism with maize food
sources was reached with honeydew on leaves, with 25.73 plus or minus 3.62 eggs for
50
control, 30.34 plus or minus 2.43 for Pactol CB (Bt 176), 34.53 plus or minus 3.67 for Pactol
(non-Bt), 29.68 plus or minus 2.44 for Novelis (Mon 810) and 35.50 plus or minus 3.33 for
Nobilis (non-Bt). In all the experiments, no significant differences were found between Bt and
non-Bt maize. There was no reduction of parasitism. The tested Bt maize cultivars Bt176 and
Mon810 can be classified as "harmless" (category 1) to T. brassicae parasitoid wasps. In the
present study, the testing method and the indicator organism of the genus Trichogramma were
shown to be suitable for future risk assessment and monitoring of transgenic crops
(Zimmerman et al., 2004). Candolfi et al., (2004) investigated the potential side-effects of Bt
maize on non-target arthropods. His study was carried out under field conditions. The
communities of non-target arthropods in the soil, on the leaves and flying in the crop area
were monitored throughout the growing season. Water-treated, untransformed maize served
as a control, and a spray application of a bacterial Bt insecticide (Delfin WG) and a synthetic
insecticide (Karate Xpress) used to control O. nubilalis acted as positive reference treatments.
Significantly lower infestations by the lepidopteran target species O. nubilalis were observed
in the Bt-maize plots compared to the control. Candolfi did not observe any effects of Btmaize on the communities of soil dwelling and non-target plant dwelling arthropods. A trend
towards a community effect on flying arthropods was observed with lower abundance of adult
Lepidoptera, flies in the families Lonchopteridae, Mycetophilidae and Syrphidae, and the
hymenopteran parasitoids Ceraphronidae. Effects were weak and restricted to two sampling
dates corresponding to anthesis. A short but statistically significant effect of Karate Xpress
and Delfin (used in Switzerland) was observed on the community of plant dwellers and a
prolonged effect of Karate Xpress on the soil dwellers (Candolfi et al., 2004). Widespread
management practices such as transgenic insecticidal crops influence the distribution and
density of targeted pest species across the agricultural landscape. Natural enemies must cope
with this altered distribution, and their response potentially influences the rate of resistance
evolution in the pest. White and Andow (2005) examined spatial patterns of parasitism by the
specialist parasitoid Macrocentrus grandii in response to the density of its host, the ECB.
When we manipulated host distribution and observed resulting patterns of wasp density and
parasitism, we found that the smallest host aggregations had the lowest parasitism, but only
when not associated with larger host aggregations. A subsequent field experiment confirmed
that proximity to large host aggregations increased parasitism in small host aggregations.
Theory indicates that such positive density-dependent parasitism should accelerate the
evolution of toxin resistance in pest species, but study suggested that close spatial proximity
between insecticidal crops and refuges may help equalize M. grandii parasitism and that
simple management techniques such as in-field refuges could potentially increase the
complementarity of transgenic and biological control of ECB in this system. Further research
is needed, however, before extrapolating the results of our small-scale study to field-level
patterns and concluding that M. grandii will necessarily hasten resistance evolution in the
ECB (White, Andow, 2005). Weber and Nietwing (2006) detected possible effects of Bt
maize on the detritophagous Allajulus latestriatus (Diplopoda, Julidae). No significant
differences in mortality, consumption of maize leaves, or weight gain were found when
animals were fed on N4640Bt compared to its isoline and the other two varieties. However,
faeces production per diplopod was significantly increased when animals were kept on Bt
maize compared to the isoline and to another maize variety. In the toxicity test, no significant
differences were found for mortality, consumption, weight gain or faeces production between
diets, not even at Cry1Ab concentrations more than 100 times higher than in Bt leaves.
Bioassays proved that the Bt protein in transgenic leaves and in faeces of diplopods was still
insecticidal. The toxicity test indicated that Cry1Ab excretion in the faeces is linearly
correlated to the Cry1Ab uptake through the diet. Our findings suggest that Bt maize and
Cry1Ab will not harm A. latestriatus. However, this diplopod excretes considerable amounts
51
of Bt protein with its faeces. The Bt protein is still insecticidally active and, thus, becomes
available to other soil organisms (Weber, Nentwing, 2006). In the mid-1990s, commercial
cultivation of transgenic insecticidal crops (Bt corn, cotton and potato) began in North
America. In 1998 and 1999, some researchers warned that these Bt crops may have
unexpected negative effects on nontarget butterflies, beneficial natural enemy insects, and soil
fauna. Since then, many peer-reviewed articles have been published about the nontarget
effects of transgenic insecticidal crops. Most subsequent studies revealed that Bt corn pollen
has no harmful effect on nontarget butterflies in the field. Negative effects on predatory or
parasitic insects shown in laboratory experiments have never been demonstrated in
greenhouse or field studies. Although assessing the effect on soil fauna is difficult compared
with on nontarget butterflies or above-ground natural enemies, none of the reports have
documented deleterious effects on soil biota. The current commercially used Bt crops appear
to have little significant adverse effect on nontarget fauna. Before the approval of commercial
field cultivation, many ecological risk assessments are imposed on new types of transgenic
crops (new trait event) and the nontarget effect is an essential part of the risk assessment for
transgenic insecticidal crops. Many further articles on the nontarget effect will be published
for transgenic insecticidal crops including the current Bt crops (Shirai, 2007). The effect of
transgenic Bt maize pollen expressing Cry1Ab toxin (event Bt 11) as a diet on longevity and
fecundity of Trichogramma ostriniae were assessed in the laboratory. The results showed that
the amount of Cry1Ab toxin detected in Bt maize pollen was 115.13 plus or minus 7.29 ng/g
fresh weight by ELISA method. Females fed on suspension of pollen of transgenic Bt maize
or non-Bt maize in water survived for a significantly longer time, parasitized more host eggs,
and emerged more offsprings than those fed on water alone, but no significant difference in
sex ratio of offspring was observed. The longevity of females fed on 10% honey alone was
similar to those fed on suspension of pollen of transgenic Bt maize or non-Bt maize in 10%
honey without significant differences in fecundity, number of progeny emerged among the
treatments. No significant differences in longevity, number of parasitized eggs, number of
progeny emerged and the offspring sex ratio were observed between the females feeding on
pollen of Bt maize and non-Bt maize, and this was also shown in experiments with suspension
of 10% honey and with water. It was so concluded that maize pollen in water increased the
reproduction and survival of T. ostriniae females compared to water alone; maize pollen of
event Bt 11 expressing Cry1Ab toxin had no adverse effect on T. ostriniae (Wu et al., 2008).
2.5.4. Mechanisms of natural control and new technics
A careful study of the problem of natural control has been convinced by many writers. This
study, what they have called the intrinsic controlling factors, is far more important in
connection with the natural equilibrum than is generally realized. They belive that in the case
of many species, more individuals disappear of their highly restricted adaptive power than
though all the other controlling factors taken together. It is propably true that in many cases
the pests are supplemented by other agencies, such as parasites and predators, but that they
surpass in importance any other single group of factors seems certain. It is difficult to make
any general statement as to the nature and action of the intrinsic factors of control
(Anonymous, 1928). Several possibilities exist for the varying degrees of succes of
parasitoids, controlling O. nubilalis population, including availability of adult food, (nectar
from flowering plants) and maintenance of O. nubilalis populations in plant species other than
maize. Native predators and parasites exert some effect on O. nubilalis populations, but
imported parasitoids seem to be more important (Hagerman, 1997). Adults of many parasitoid
species are known to exploid plants for food by using nectaror secretions from aphids or scale
insects (Van Emden, 1963, 1990; Jervis et al., 1993). Many studies have shown that an
52
increase in structual diversity in agroecosystems leads to a greater diversity of both pests and
benefical insects that often results in less damage by the pest (Risch et al., 1983; VanEmden,
1990). This increase in insect diversity with structual diversity appears to be the result of two
correlated factors: increased plant species diversity and increased plant architectural
complexity (Lawton, 1983). Hawkins and Lawton (1987) found that parasitoids respond
strongly to increased plant architectual complexity, exhibiting the lowest diversity on
monocots and herbs and the highest on trees and shrubs (Hawkins, Lawton, 1987).
2.5.4.1. Influence of vegetation and natural conditions on the parasitoids of Ostrinia
nubilalis
Weather conditions and plant architecture were monitored during the experiments of Wang et
al., (1997). The results indicated that percentage of eggs parasitized was negatively related to
an increase in leaf area as well as an increase in the distance at which eggs were located from
the point of release of wasps. Eggs distributed on plants at different directions from the
release point received different levels of parasitism. Eggs that were stapled onto leaves in the
upper third of a maize plant received much less parasitism than those on the middle and lower
third of the plant. Higher mean temperature adversely affected the level of parasitism during
hotter times of the season and conversely, lower temperatures (<17 deg C) reduced the egg
parasitism during cooler times of the season. The longer the exposure of eggs to wasps, the
higher the level of egg parasitism. However, the levels of egg parasitism for 2 days' exposure
were almost the same as that for 3 days' exposure due to the limited longevity and egg-laying
behavior of the wasp. These results suggest that inundative releases of Trichograma ostriniae
should be made every two to three days, with multiple release points per hectare. In addition,
weather conditions and plant architecture, especially temperature, plant height and leaf area
must be taken into consideration to optimize levels of parasitism (Wang et al., 1997). Bruck
and Landis (1999) sampled natural enemies of O. nubilalis. Observational studies were
conducted in 1995 and 1996 along field borders with differing vegetation levels. Maize fields
adjacent to three broad classes of border vegetation: herbaceous, intermediate, and wooded,
were studied. A maize field adjacent to each border class was sampled along the entire length
of its respective border. O. nubilalis larvae collected were evaluated for presence Nosema
pyrausta (Paillot) (Microspora: Nosematidae) and the parasitoid Macrocentrus grandii
Goidanich (Hymenoptera: Braconidae). There was a negative interaction noted between
larvae parasitized by M. grandii and O. nubilalis larvae infected with N. pyrausta. This
antagonism between the two biotic factors may explain why increased food and shelter
adjacent to maize bordering diverse vegetation did not result in significantly higher parasitism
in limited observations (Bruck, Landis 1999). Many agroecosystems are unfavorable
environments for natural enemies due to high levels of disturbance. Habitat management, a
form of conservation biological control, is an ecologically based approach aimed at favoring
natural enemies and enhancing biological control in agricultural systems. The goal of habitat
management is to create a suitable ecological infrastructure within the agricultural landscape
to provide resources such as food for adult natural enemies, alternative prey or hosts, and
shelter from adverse conditions. These resources must be integrated into the landscape in a
way that is spatially and temporally favorable to natural enemies and practical for producers
to implement (Landis et al., 2000). Parasitoids and their hosts , exept the conection between
them, very often involve another sources – plants. Neonate Lepidoptera are confronted with
the daunting task of establishing themselves on a food plant. The factors relevant to this
process need to be considered at spatial and temporal scales relevant to the larva and not the
investigator. Neonates have to cope with an array of plant surface characters as well as
internal characters once the integument is ruptured. These characters, as well as microclimatic
53
conditions, vary within and between plant modules and interact with larval feeding
requirements, strongly affecting movement behavior, which may be extensive even for such
small organisms. In addition to these factors, there is an array of predators, pathogens, and
parasitoids with which first instars must contend. Not surprisingly, mortality in neonates is
high but can vary widely. Experimental and manipulative studies, as well as detailed
observations of the animal, are vital if the subtle interaction of factors responsible for this
high and variable mortality are to be understood. These studies are essential for an
understanding of theories linking female oviposition behavior with larval survival, plant
defense theory, and population dynamics, as well as modern crop resistance breeding
programs (Zalucki et al., 2002). Weeds and arthropods interact in agricultural systems. Weeds
can directly serve as food sources or provide other ecosystem resources for herbivorous
arthropods, and indirectly serve carnivorous (beneficial) arthropods by providing food and
shelter to their prey. Weeds can serve as alternative hosts for pest and beneficial arthropods
when their preferred crop host is absent. Herbivory on crops by pest arthropods reduces the
competitive ability of crop plants, leading to increased weed growth. Interactions between
weeds and arthropods have several implications to integrated pest management (IPM). Pest
and beneficial arthropod populations can be maintained in the absence of crop hosts. This
statement also applies to all other pests that use weeds as a food source, including pathogens,
nematodes, mollusks, and vertebrates. Weeds outside crop fields that maintain overwintering
populations of arthropod pests are the major reason for the development of area-wide IPM
programs for certain mobile arthropod pests. Weeds can serve as a source of increased
diversity in agroecosystems. Increased diversity has been the rationale for enhancing
biological control of arthropod pests through habitat management. The consequences of such
approaches are difficult to predict on a multispecies IPM basis (Norris, Kogan, 2004).
Tremendous strides have been made regarding our understanding of how host plant chemistry
influences the interactions between herbivores and their natural enemies. While most work
has focused on plant chemistry effects on host location and acceptance by natural enemies, an
increasing number of studies examine negative effects. The tritrophic role of plant chemistry
is central to several aspects of trophic phenomena including top-down versus bottom-up
control of herbivores, enemy-free space and host choice, and theories of plant defense.
Furthermore, tritrophic effects of plant chemistry are important in assessing the degree of
compatibility between biological control and plant resistance approaches to pest control.
Additional research is needed to understand the physiological effects of plant chemistry
onparasitoids. Explicit tests are required to determine whether natural enemies can act as
selective forces on plant defense. Finally, further studies of natural systems are crucial to
understanding the evolution of multitrophic relationships (Ode, 2005).
Parasitoids of phytophagous insect use olfactoty cues for host location. In long range
orientation, volatile cues emanating from plants are used for locating habitats where hosts
likely to be present. Some parasitoids, however, are attracted to odors of only certain food
plants of treir hosts (Shahjahan, 1974; Elzen et al., 1983; Ding et al., 1989; Navasero, Elzen,
1989; Matrin et al., 1990; cit. Udayagiri, Jones, 1992). This is likely to affect the range of
plants on which their hosts are parasitised. Up the searching behavior of a parasitoid in the
field can be increased by application of attractive plant odors, then this strategy can be
incorporated in in biological control programs for retaining a parasitoid in a habitat or
introducing it to a less preferred habitat. For their efficient use in biological control programs,
attractive plant compounds need to be identified. Plant odors contain numerous compounds of
which only some may be critical for parasitoid attraction. Plant compounds involved in
interactions between plants and parasitoids are termed synomones (allelochemicals that
mediate mutually beneficial interactions) (Nordlund, Lewis, 1976). For many parasitoid
species, the final step of host location occurs on plants whose structure varies in time and.
54
space, altering the capacity of parasitoids to exploit hosts. Plant structure can be defined by its
size, heterogeneity and connectivity. Gingras et al., (2002) tested the hypothesis, that these
three components and all possible, interactions affect the level of parasitism of Trichogramma
evanescens and that parasitism can be predicted if the structure of a plant is measured.
Gingras quantified and varied the structure of three-dimensional artificial plants to determine
which component(s) of plant structure explain variability of parasitism and to develop a
model that predicts parasitism by Trichogramma females. This model was validated with
three natural tritrophic systems. The experiment with artificial plants revealed that plant
structure affected host-finding, success, which was higher on plants with a simple structure
and low on plants with a complex structure. A response surface regression showed that the
linear and quadratic terms of connectivity were highly significant, indicating that connectivity
best explained the variability in the rate of parasitism obtained. The interaction between
connectivity and heterogenity was also significant. Observed values of parasitism from
experiments with three natural tritrophic systems fit predicted values of parasitism generated
by the model, indicating, that parasitism can be predicted if heterogenity and connectivity of a
plant are known (Gingras et al., 2002).
2.5.4.2. Use of modern technologies and the biological control
With the development of monoclonal antibody (Mab) technology, reagents with the
specificity nessesary for distinguishing among insect genera species, and life stages on a
biochemical basis have become available (Lenz, Greenstone, 1988, Ragsdale, Kjer, 1989,
Greenstone et al., 1991, Hagler et al., 1991, cit. Stuart, Burkholder, 1991). Unlike visual
examination, immunoassays that employ Mabs are expensive, rapid, sensitive, and simple to
perform (Greenstone, Morgan, 1989, Stuart, Greenstone, 1990, cit. Stuart, Burkholder, 1991).
The use of natural enemies for biological control of insects is an integral of a successful
integrated pest management program. An understanding of the chemical ecology of insect
parasitoids can help to make their use more efficient. This includes the study and
identification of sex pheromones of parasitoids, since such pheromones can be used to assess
the activity of parasitoids, to monitor their density, and to predict rates of host parasitism
(Shu, Jones, 1993). Wasp parasitoids use a variety of methods to commandeer their insect
hosts in order to create an environment that will support and promote their own development,
usually to the detriment of the host insect. Parasitized insects typically undergo developmental
arrest and die sometime after the parasitoid has become independent of its host. Parasitoids
can deactivate their host’s immune system and effect changes in host hormone titers and
behavior. Often, host tissues or organs become refractory to stimulation by tropic hormones
(Beckage, 2004). Agusti et al., (2005) have developed specific molecular markers to detect
Lydella thompsoni (Herting) and Pseudoperichaeta nigrolineata (Walker) (Diptera:
Tachinidae) within the O. nubilalis. Primers amplifying fragments of the mitochondrial COI
gene were designed following alignment of comparable sequences for a range of parasitoid
and host species. Each of the primer pairs proved to be species specific to a tachinid species,
amplifying DNA fragments of 191 and 91 bp in length for L. thompsoni and P. nigrolineata,
respectively. This DNA-based technique allowed molecular evaluation of parasitism in
natural populations. In order to study the geographical distribution of both species in France,
O. nubilalis diapausing larvae in maize stalks were collected from 12 locations over the whole
country. The molecular evaluation of parasitism was compared with the traditional method of
maintaining O. nubilalis populations in controlled conditions before breaking off the
diapause. The percentage parasitism found in both species of tachinids was higher approximately three times - using the molecular method, suggesting an underestimation by the
traditional rearing protocol. Tachinid parasitism on O. nubilalis was not significantly different
55
between geographical areas (south, central and north France) for both species. Agusti’s study
shows that molecular methods are very promising for the correct detection and identification
of tachinid parasitoids in natural field populations (Agusti et al., 2005).
Another way, how to reduce the population of O. nubilalis, is using the agents of biological
control. Biological control requires specific tools for the accurate detection and identification
of natural enemies, and to detect unusual variations in their density, which may follow
changes in agricultural practices. Natural enemies used for biological control often go through
genetic bottlenecks during collection, rearing and subsequent eatablishment in the field. Such
bottlenecks reduce genetic variability, which is thouhgt to impede population’s ability to
adapt to a new enviroments and, therefore, its potential for the biological control (Unruh et al.,
1983). When a population is imported for biological control and is cultured in the laboratory
for several generations, sex allels are likely to be lost from the culture. Initially, the field
sample propably contains only a subset of the sex allels present in the population from which
the imported individuals were collected. A further reduction occurs through genetic drift and
inbreeding during the laboratory rearing, particularly if the cultures experience periodic
reductions in population size (Unruh et al., 1984). Before parasitoids and predators are fully
endorsed as biological control agents in storage facilities, a reliable technique must be
development to determine how much they contribute to the overall insect contamination of
commodities. Determining of the origin of insect fragments by visual examination is difficult,
labor-intensive, and requires special skills (Stuart, Burkholder, 1992).
2.5.4.3. Role of order Hymenoptera
In Hymenoptera, reduced genetic variability causes an additional problem: The production of
diploid males from fertilized eggs. The occurrence of diploid males is a consequence of the
sex-determining mechanism in certain Hymenoptera-i.e., a single-locus, sex-determination
mechanism first described by Whiting and his students (reviewed in Whitings studies sex
determination in Bracon hebetor, said and found that haploid individuals were always males,
wheras diploid individuals were generally females. However, under inbreeding conditions
some diploid individuals were generally males. Diploid males, once known only from B.
hebetor and some bees, have recently been reported in five species of Ichneumonoidea (Clark
et al., 1963; Unruh et al., 1984; Hedderwick et al., 1985; Steiner, Teig, 1989; W. W. M.
Steiner, cit. Stouthamer et al., 1992). The generality of this single-locus sex determination to
the Ichneumonoidea still remains to be determined. Additionally, diploid males also have
been found in three species of sawflies and several social hymenoptera. Chalcidoidea
apparently have some other mechanism of sex determination because diploid males did not
appear when these species were inbred (Schmieder, Whiting, 1946; Whiting, 1960; Skinner,
Werren, 1980; Luck et al., 1992; cit. Stouthamer et al., 1992). Diploid males have been
known to occur in several braconid and ichneumonid species too. These diploid males are the
result of a single-locus, sex-detrmination mechanism. Heterozygotes at this sex locus develop
into females, whereas hemizygotes (haploids) and homozygotes (diploids) develop into males.
Diploid males have a low fertility and their frequency drastically increases with small
populations or ombreeding. The implications of this sex-determining mechanism for the use
parasitoids in biological control were explored. Production diploid males leads to male biased
sex rations and can reduce rates of establishment and population growth. Taxa in which a
single-locus sex determination has been found (e.g., Ichneumonidae, Braconidae) often
experience extreme male-biased sex rations in mass rearing and have been more difficult to
establish than taxa with other modes of sex determination (e.g.,Chalcidoids). The effect of
laboratory rearing on the number of sex allels, frequency of of diploid males, and
56
popolationgrowth rates were explored by computer simulatin. Methods of rearing and release
that could enhance the the number of sex allels and the establishment of parasitoids were
discussed. Furthermore additional small-scale releases may enhance effectiveness of alredy
established populations by increasing number of sex allels and the rate at which their
population grows (Stouthamer et al., 1992). Antolin et al., (2003) observed besides haplodiploid sex determination, where females develop from fertilized diploid eggs and males from
unfertilized haploid eggs, some Hymenoptera have a secondary system called complementary
sex determination (CSD). This depends on genotypes of a 'sex locus' with numerous sexdetermining alleles. Diploid heterozygotes develop as females, but diploid homozygotes
become sterile or nonviable diploid males. Thus, when females share sex-determining alleles
with their mates and produce low fitness diploid males, CSD creates a genetic load (Antolin et
al., 2003). The loss of sex allels results in two detrimental effects on these biological agents:
(1) a male-biased sex ratio and (2) a reduced growth rate of the wasp population. The
frequency of females in a parasitoid population is important because only females are
effective biological control agents. The number of the female offspring produced per female
is also an important determinant of a population’s growth rate, the more daughters produced
per mother, the faster a population can increase and the faster a pest is suppressed. Also, the
higher the population’s growth rate the better the chance that the wasp become established in
the first place. Small differences in the growth rate of the released agent make a large
difference in the abundance of the parasitoid in a few generations. For instance the production
of seven versus five daughters per female results in a more than a 5-fold difference in total
number of females in the fifth generation (Stouthamer et al., 1992). The occurrence of diploid
males in a population reduced the potential growth rate of the population because some
fertilized eggs became diploid male eggs that either died during development or became male
adults. These diploid males would normaly have been females. Also, females inseminated by
diploid males produced only haploid sons or triploid (sterile) daughters. How severaly the
population growth rate is affected depends on two factors: (1) the number of allels at the sex
locus and (2) the mating system (Stouthamer et al., 1992). Theoretically, single-locus sex
determination substantially influences the sex ratio and the population growth of parasitoid
species. Both factors affect the biological control potential of parasitoids. Although scan data
exist on the distribution of this sex-determining mechanism among the Hymenoptera, what
data exist suggested that single-locus sex determination was limited to some, if not all,
Braconidae and Ichneumonidae. Chalcidoidea seem to possessed another sex-determining
mechanism (Luck et al., 1992).
The vast majority of braconids are primary parasitoids of other insects, especially upon the
larval stages of Coleoptera, Diptera, and Lepidoptera but also including some hemimetabolus
insects (aphids, Heteroptera, Embiidina). As parasitoids they almost invariably kill their
hosts, although a few only cause their hosts to become sterile and less active. Both external
and internal parasitoids are common in the family, and the latter forms often display elaborate
physiological adaptations for enhancement of larval survival within host insects, including the
co-option of endosymbiotic viruses for compromising host immune defenses (Stoltz and
Vinson, 1979; Stoltz, 1986; Whitfield, 1990; Beckage, 1993, Stoltz and Whitfield, 1992;
Whitfield, 2002; Whitfield and Asgari, 2003). Early larval development in braconids has also
yielded surprises, such as the discovery of relatively closely related genera that differ in such
import aspects as syncitial versus holoblastic cleavage, normally characterizing major animal
phyla (Grbic and Strand, 1998; Grbic, 2000). Several excellent general reviews of braconid
biology are available (Matthews, 1974; Shaw and Huddleston, 1991; Shaw, 1995; Wharton,
1993).
57
2.5.4.4. Natural predators of Ostrinia nubilalis
O. nubilalis populations, like those of other insect species, fluctuate indensity from year to
year (Chiang, 1961). Chiang and Hodson (1972) suggested, that density independent factors
are primarily responsible for such fluctuations in populations of this pest. Agricultural
practices, natural enemies, and varied climatic factors are commonly viewed as regulating
agents. There are factors – the number of females in the 1st flight, average rainfall per day
during the 1st flight, and the average daily temperature during the 1st flight-could be used to
forecast borer infestations (Barlow et al., 1963). To find natural enemies of O. nubilalis is one
way of natural control. Numerous studies were conducted under laboratoy and natural
conditions to identify parasitic wasps with the potential to control pest insects (Stuart,
Burkholder, 1991). There are also some parasites which attack corn borer eggs. Overall,
parasites have a low impact on the population. There is some evidence that the level of
predatory insects in maize fields can be influenced by farm management practices. The use of
insecticides, including those applied at planting, reduces the predator population. In no-till
systems the level of predators has been reported to increase. A few insect pathogens (diseases)
can become important mortality factors, especially during prolonged periods of wet weather.
Corn borers killed by these pathogens will often have mold growing on the body (Hagerman,
1997).
2.6. Parasitoids of Ostrinia nubilalis and their bionomy
The parasites of European corn borer, Ostrinia nubilalis has been described by various
writers. The more general phases of the work in Europe were presented by Thomson and
Parker (1928, 1930). Numerous papers treating specific species published by Thompson and
Thompson (1921, 1923), Parker (1931a, 1931b), Parker and Smith (1933), Vance (1931,
1932a, 1932b), Smith (1932) were concerned pricipally with the general status of the various
species in Europe, in conjuction with their morphology and laboratory biology.
2.6.1. Lydella thompsoni Herting
Order: Diptera
Family: Tachinidae
The tachinid flies (family Tachinidae) is by far the largest and most important group of insect
parasitic flies, with over 1300 species in North America. All species are parasitic in the larval
stage, and many are important natural enemies of major pests. Many species of tachinids have
been introduced into North America from their native lands to suppress populations of alien
pests. Tachinid flies differ in color, size, and shape, but many somewhat resemble house flies.
They usually are either gray, black, or striped, and often have many distinct abdominal
bristles. Most tachinids attack caterpillars and adult and larval beetles. Other species kill
sawfly larvae, various types of true bugs, grasshoppers, or other types of insects. There are
many important pests in the North Central states that are suppressed by tachinids. Egg laying
varies considerably. In some species, eggs are deposited on foliage near the host insect. After
the eggs hatch, the maggots are ingested during feeding by the host, such as a caterpillar, and
then develop inside the host. In other species, the adult fly glues her eggs to the body of the
host. Conspicuous white eggs up to 1 mm in size can sometimes be seen on the head or body
of a caterpillar or other host. After the eggs hatch, the maggots penetrate into the host's body.
Some adult female tachinids possess a piercing ovipositor and actually insert the eggs inside
the host body. Many tachinids exhibit an unusual trait in that the eggs mature within the
58
mother fly, which then lays eggs that immediately hatch. In some species, egg hatching
actually occurs within the mother fly, and she gives birth to living young. Egg and larval
development are rapid for most tachinids, and pupation often occurs within 4-14 days after
egg laying. The pupal period generally lasts 1-2 weeks. Many species are capable of several
generations per year, but others are restricted to only one generation, especially if their hosts
have only a single generation. Most, if not all, tachinids are internal parasites within their
hosts. Most species are solitary, but some are gregarious, with anywhere from 2-3 up to a
dozen or more capable of developing within a single host. This is a very important family in
natural control of many pests, and many have been introduced and successfully established in
biological control programs. However, none are currently being sold commercially. The
tachinid flies, and many others not mentioned, can be important in natural control (Mahr,
Mahr, 1997). L. thomsoni is a wide spread parasitoid. In Europe this parasitoid has been
observed (Stengel, 1975, 1982; cit. Cagáň et al., 1999), southern Germany (Engel, 1971; Reh,
1985; cit. Cagáň et al., 1999), Poland (Kania, 1962; cit. Cagáň et al., 1999), eastern Hungary
(Bánk, 1972; cit. Cagáň et al., 1999), former (Yugoslavia Hergula, 1929, 1930; Manojlovic,
1984, 1989, Manojlovic et al., 1994; cit Cagáň et al., 1999), Romania (Lehrer, 1982 Rosca
and Barbulescu, 1983; cit. Cagáň et al., 1999), France (Galichet et al., 1985; Grenier et al.,
1990; cit. Cagáň et al., 1999), Switzerland (Kaufmann et al., unpubl. Data, cit. Cagáň et al.,
1999), Italy (Maini, 1974; Barbatini, 1986; cit. Cagáň et al., 1999), Spain (Eizaguire et al.,
1990; cit. Cagáň et al., 1999), and Russia (Chao You Chin, 1960; cit. Cagáň et al., 1999).
According to Bírová (1962), L. thomsoni parasitized 1.1% – 6.0% of O. nubilalis larvae in
southwestern part of Slovakia. In the same part of Slovakia less than 1% parasitation was
observed during 1987 – 1991 (Cagáň, 1993). The parasitation was 1.64% – 2.11% during
1993 –1995 (Cagáň et al., 1999). A relatively high level of parasitism by L. thomsoni was
found in the location of Kráľovský Chlmec (eastern part of Slovakia). In 1991 Cagáň (1994)
recorded 16% of parasititation O. nubilalis larvae and during 1993 – 1995 the parasitation at
this locality reached 4.34%, and 21.95% and 7.92% in each year respectively (Cagáň et al.,
1999). Within Central Europe, parasitism of the O. nubilalis by the tachinid parasitoid, L.
thompsoni increased from 0.47% to 1.49% in south-western Poland (51 degree 03'N), to
4.31-21.95% in eastern Slovakia (48 degree 20'N). The synchrony between the parasitoid and
its primary host, O. nubilalis was studied in Central Europe under conditions where the host is
univoltine, but the parasitoid is bivoltine (Cagáň, 1999). Monetti et al., (2003) observed that
the most frequently found species on non-overwintering larvae of O. nubilalis and S.
nonagrioides (pink stem borer) was L. hompsoni. Differences in percentage of parasitism (PP)
between O. nubilalis and S. nonagrioides were significant. L. thompsoni was also the
dominant parasitoid on overwintering larvae. Its PP was higher on O. nubilalis than on S.
nonagrioides. The correlation between number of stem borer per plant and percentage of
parasitised larvae was not significant, neither for S. nonagrioides nor for O. nubilalis.
Shannon-Wiener index as a measure of parasitoid diversity was similar in the different hosts.
In conclusion, a very low parasitoid natural control on corn borers, in hybrid maize crops
grown at the province of Pontevedra (NW Spain) was found. Stem borers seem to be
protected from parasitoids by several circumstances, specifically the development of their
immature stages within refuges (the stalks), but other factors probably would contribute to the
situation (Monetti et al., 2003).
The females of L. thompsoni are able to copulate after five hours in the day when they have
flown fly off. It is the time when their wings are not able to fly (Baker et al., 1949). Females
of L. thompsoni can lay their eggs right into the holes in stalks of maize, where are the O.
nubilalis larvae. The adult females are attracted with the smell from frass and excrements
produced by O. nubilais larvae. L. thompsoni is able very succesfully attack all instars of O.
59
nubilalis, exept the first larval instar. The larvae of the last instar vere the most attacked 54 %.
The parasitoid is able to get into the host body through the trachea, through the area between
the parts of the body or through the anal hole (Paillot, 1928; Baker et al., 1949; Cagáň, 1999).
The females retain their eggs inside their body until each larva is ready to hatch. Each female
is capable of producing up to 1,000 eggs, although far fewer are deposited or ever find a host
borer. After the eggs have incubated for about 5 days, the female fly finds a potential host.
She runs hurriedly along a stalk and appears to be searching from side to side. She is attracted
to volatiles produced from host frass pushed out of the borer tunnel, and may "taste" the frass
when it is encountered. Hatching usually takes place just as the female is depositing her
offspring. Living larvae are deposited at the entrance to the host tunnel. The female stands
over the burrow, bends her abdomen under until the ovipositor is pointing downwards, and
then a larva wriggles out or is brushed off with a quick movement of the tip of the abdomen.
This first instar must then move into the tunnel and find its way to the borer. It prefers to
attack fourth instar borers. (Mahr, Mahr, 1997). After the penetration host body, the larva
inside, can catch with the back part of her body to the lateral tube of host tracheal system,
where the larva stays till the time of parasitoid mature. The adult larva of L. thompsoni
overwinters inside the body of host (Paillot, 1928; Baker et al., 1949; Cagáň, 1999). In the
host, the maggot feeds first on the body fluids, then on the fatty tissues and internal organs.
Upon the death of the borer, the maggot forces an opening in the skin, but continues to feed
until its development is complete. It then leaves the host remains and pupates in the tunnel
nearby. Larval development takes about 8 days and another 8 days is spent in the pupal stage
(Mahr, Mahr, 1997). In Slovakia, the pupa of L. thompsoni is formed in the second part of
March, 50% of pupation was surpassed in the first half of April (Cagáň, 1999), inside the
overwintering body of O. nubilalis and the adults hatch at the end of April, but the majority at
the beginning of May. Development treshold temperatures for 50% pupation was determined
to be 2.7 °C, and for 50% adult emergence 5.0 °C; the respective thermal constance were
178.8 – 179.8 and 237.7 – 251.8 °C days. The adults of L. thompsoni hatch very early in the
spring, they do not attack O. nubilalis larvae during the period of hibernation, but they can
create one population on the alternative host. (Dudich, 1928; Hergula, 1929; Cagáň, 1999;
Kuske et al., 2004). There were also found cocoons in the stalks of maize and these cocoons
were caught to the head of the death host (Dudich, 1928; Hergula, 1929). Parasitation of O.
nubilalis larvae by L. thomsoni continued until the end of July. The first parasitoid adults from
this second generation emerged in the second half of August. By the end of the season, nearly
one-third of L. thompsoni adults had emerged. The rest of this generation apparently
overwintered in the larval stage (Cagáň,1999). The population of L. thompsoni can be also
negative influenced with another egg parasitoid Trichogramma brassicae which is used to
control O. nubilalis. Inundative releases of T. brassicae coincide with the oviposition period
of the alternative hosts of the tachinid. T. brassicae moving out of release fields may attack
and diminish the population of these hosts, creating a bottleneck situation for L. thompsoni in
the subsequent spring. Laboratory host specificity tests in Switzerland showed that the
tachinid’s two most abundant spring hosts Archanara geminipuncta Haworth (1809)
(Lepidoptera, Noctuidae) and Chilo phragmitellus Hübner (1805) (Lepidoptera, Crambidae)
are successfully parasitised by T. brassicae females in no-choice situations. Kuske et al.,
(2004) tests showed, that the two tested spring hosts escape parasitism since their eggs are
well hidden or not attractive. Negative effects of inundative releases of T. brassicae on the
native tachinid fly L. thompsoni, such as population density reduction, displacement, or local
extinction, are very unlikely (Kuske et al., 2004).
60
2.6.2. Sinophorus turionus Ratz
Order: Hymenoptera
Family: Ichneumonidae
Ichneumonidae – common names ichneumon, 1-10mm in length, non-metallic coloration
(typically black, orange, brown), usually larger than braconids; quite variable in color, two
recurrent veins, vein 2m-cu of forewing present and with vein 1/Rs+M absent, vein 1r-m of
hind wing usually opposite or apical to basal separation of R1 and Rs, metasomal tergum 2
and 3 separate, antennae apparently with 16 or more segments, females often with long
ovipositors. Species in the family Ichneumonidae are separated from those in Braconidae by
having two, rather than one or zero recurrent veins. The biology varied. Mainly primary
endoparasitoids of holometabolous larvae or Chelicerata. Primarily attack Symphyta and
Lepidoptera (Foltz, 1998). Ichneumon wasps, with a few exceptions, are parasitoids of insects
and other arthropods. Most exist in the larval state within the bodies of caterpillars of
butterflies and moths (Silverside, 2003). This ichneumonid, also named, Eulimneria
crassifemur, Limnerium alkae, Eulimneria alkae, Campoplex alkae, Sinophorus alkae, was
originally described by Thomson (1887) from Sweeden, and is widely distributed throuhgout
the Europe. Paillot (1924) has recorded this ichneumonid as a parasite of the catepillars of
several Microlepidoptera, such as Clysia ambiguella (Hübn.) and Polychrosis botrana
(Schiff.) A parasite said to differ slightly from it, but which closely resembles it in habits and
may really be identical with it, has been reared by Paillot (1924) in the Rhone Valley from
larvae of the pech- leaf sawfly Neurotoma nemoralis. It is one of the most consistant parasites
of corn borer and has been found attacking it both in maize and weeds in every part of Europe
with the exeption of the French Mediterranean coast (Anonymous, 1928). S. turionus bears a
close resemblance to another ichneumonid parasite, Eriborus terebrans (Gravenhorst) in both
the adult and larval stages. The adult of S. turionus may be distinquished by the presence of
an areolet in the forewings, which is lacking E. terebrans (Baker et al., 1949). S. turionus is
one of the most widespread larval parasitoid, generally distributed throughout most of the
countries of Europe (Baker et al., 1949) and in Slovakia (Bokor, 1998). According to Cagáň
and Bokor (1999) parasitation ranged around 0.76% – 2.72% in southwestern part of Slovakia
(location Nitra) and 0.24% – 2.72% in eastern part of Slovakia (location Kráľovský Chlmec)
during 1993 – 1995. During the three years study conducted in Slovakia was the parasitation
of O. nubilalis larvae with S. turionus 0.76% – 2.04%. The adults of parasitoid were hatching
through the period 17. – 31. March, 27. March, 11. April, 21 – 27. April in the years 1994,
1995, 1996. The cocons were watched in October (Cagáň, Bokor, 1998).This parasite proved
to be most important at Keszthely where the parasitation gets 8.8%. This observation reached
Sachtleben (undated) which were the same as Thomson and Parker (1930) and Paillot (1929),
that usually more than one parasite egg was deposited in larva. In the condition of the middle
Europe the first adults of S. turionus emerged since the end of March to the beginning of May
(Zwölfer, 1928; Dudich 1928; Thomson, Parker, 1928; Hergula, 1929; Manojlović, 1984), in
Keszthely Hungary was the first imago (female) observed in July 7 (Sachtleben, undated), in
Germany in April (Zwölfer, 1928). In the laboratory conditions the parasite larvae pupated on
July 28 and 30, and on August 1, 11, and 30. The imagos emerged 9 –16 days later from
August 5 to September 15. The development in the field is apparently similar, since on
August 4 cocoon were found in maize plant (Sachtleben, undated). In the 1930 the first imago
of S. turionus on the maize was found on the beginning of June in Germany. In the same time,
there were also the first parasitated larvae of O. nubilalis found (Sachtleben, 1930). In
Germany S. turionus spins cocoons from late September to the end of November. The
cocoons differ in size and colour. The size varies from 7 mm to 13 mm in length. The
61
majority measure 9 mm, in length 3 mm in widht. The colour is sometimes dark brown,
sometimes light brown or grayish brown with a paler belt (Zwölfer, 1928).
The adults are strong fliers and unlike many parasites that linger for some time in the general
vicinty of the release cage, usually make long high flights when liberated (Baker et al., 1949).
The adult have shed old pupal skin, chews an irregular hole about 2mm. In diameter slightly
to one side of the end of the cocoon and, passing through this, makes its way to the outside
through the O. nubilalis tunnel. The adult S. turionus is an active, nervous insect witch is
seldom motionless and is quickly attracted to the light (Thomson, Parker, 1930). The females,
fertilized or not, oviposit freely in the smaller catepillars of the corn borer (Anonymous,
1928). They lay their eggs into the last segment of the body of O. nubilalis larvae. The most
proper for parasitation are the larvae of the thirth or fourth instar (Jones, 1929; Baker et al.,
1949; Manojlović, 1984; Sachtleben, undated). The egg when first deposited is white in
colour but darknes rapidly, becoming brown in the course of a few hours (Anonymous, 1928).
Females are not able to recognize parasitated larvae from the healthy larvae and that is why, it
is possible to find more than one egg inside the cavity of host body. Most of these eggs die
(Pailot, 1928; Thomson, Parker 1930). This is the most important natural cause of dectruction
in the case of S. turionus, when only one egg comes to maturity (Anonymous, 1928;
Sachtleben, undated). The eggs float freely in the body cavity of the host, but by reason of the
peristaltic movements of the intestine and the circulation of the blood they soon come to be
lodged in the extreme posterior end of the larva among the Malpighian tubes (Thomson,
Parker 1930). Young larva, short time after hatching, begins to secrete and pour into the blood
of the host a cytolityc enzyme fatal to younger larvae and that is another reason why only one
larva can live inside the host (Anonymous, 1928). The larva of parasitoid is free inside the
body cavity of the host, till the last instar of her life cycle, when the larva starts to feed on the
host innards, till thsese are completely distroyed. Adult larva creates pupa very short time
before the host dies (Thomson, Parker 1930; Anonymous, 1928). The presence of a live S.
turionus larva in the body cavity of the host catepillar does not seem to affect the health of the
latter at least during the parasite first stage, for during this period the parasite is very small
and seems to procure its nourishment without attacking the organs of its host. As the parasite
larva grows it molts at least twice and by the time it reaches the third stage it occupies three –
fourths of the body cavity of its host. At about this stage the S. turionus larva absorbs the
material of the hosts organs and when is full fed it pierces a small hole in the skin of the now
dead corn borer, pushes its way out and spins its cocoon. The prepupa is very much like the
larva axept that it is less arched dorsally, slightly more pointed anteriorly and somewhat more
yellowish colour. The red eyes can be seen beneath the old larval skin as can the other
imaginal disks. The winter cocoon varies from light grey to almost black. It is oblong oval of
solid texture, the lighter colored specimens exhibit a faint whitish ring around the middle, but
in the dark specimens no such ring is visible. The prepupal and pupal period of the summer
generation is completed in from about 15 to 20 days (Thomson, Parker 1930). The larvae of
summer generation rapidly transform, issuing as adults in 10 or 12 days, but those of the fall
generation hibernate in the cocoon, transforming the following spring (Anonymous, 1928). In
the cocoons of the winter generation this phase may require four or five months. (Thomson,
Parker 1930). Laboratory experiments indicate that S. turionus is capable of living long period
(70 to 75 days) at moderate temperatures. A considerable proportion of the early adults can
thus survive until young larvae begin to appear in the field. It is possible, however, that these
adults attack other lepidopterous larvae which appear earlier than O. nubilalis and even that
under some conditions they might complete a generation before attacking the corn borer. But
no direct evidence of such an intermediate generation has been found, and it has not been
possible to carry out the extensive investigations necessary to determine wheter S. turionus
attacks other hosts (Anonymous, 1928). Baker et al., (1949) in his work recovers records from
62
New england which indicated that the species has been able to reproduce following a summer
generation in the field (Baker et al., 1949). Baker and Arbuthnot (1933) observrd important
factor that would militate against another summer generation – its lack of seasonal rhythm
with the host, which was discused by them. Baker et al., (1949) observed hyperparasites
which have appeared in material with coccons of S. turionus imported from Europe. Six
species of secondary parasites have been recorded as attacking S. turionus and at time
chalcidoids have appeared from imported coccons, especially of Italian origin (Baker et al.,
1949).
2.6.3. Eriborus terebrans Gravenhorst
Order: Hymenoptera
Family: Ichneumonidae
This parasitoid was also named as Horogenes terebrans, Horogenes punctorius, Dioctes
punctoria, Inareolata punctoria, Angitia punctoria, Diadegma terbrans. In Europe, this
parasitoid was recorded in south – west part of France (Thompson, Parker, 1928; Riffiod,
1976, cit. Bokor, Cagáň, 1999), in the north part of Italy (Maini, Platia, 1975; Barbatiny,
1986, cit. Bokor, Cagáň, 1999), Yuogoslavia (Hergula, 1929; 1930; Manojlović 1984, 1989;
Manojlović et al., 1994, cit. Bokor, Cagáň, 1999), in Hungary (Thomson, Parker, 1928;
Sachtleben, 1930, cit. Bokor, Cagáň, 1999), in Russia (Ellinger 1930 cit. Bokor, Cagáň,
1999), in Japan, Korea, China (Cartwright, 1933; Clark, 1934, cit. Bokor, Cagáň, 1999).
This ichneumonid parasitoid, was first introduced into the United States in 1920 from Europe
and Asia for control the O. nubilalis (Thompson, Parker, 1928; Ma et al.,1992). The
parasitoid became established throughout the norhern maize belt, where is now one of two
prevalent parasitoids of O. nubilalis (Winnie, Chiang, 1982, cit. Ma et al.,1992). E. terebrans
adults are more abundant, and parasitise a greater proportion of O. nubilalis larvae, near
wooded edges of maize fields. It was hypothesized that E. terebrans requires a source of sugar
and a moderate microclimate available in the woodlot, but not in the maize field E. terebrans
needs habitats adjacent to maize fields for sources of sugar and a moderate microclimate
unavailable in early season maize (Dyer, Landis, 1996). Dyer and Landis (1997) continued in
their work and they tested within-field distribution of adult E. terebrans. They used a malaise
traps near a wooded edge, near an herbaceous edge, and in the field interior in each of 4 fields
of maize. During the 1st generation of 1991, significantly more females were captured in
wooded-edge traps than in herbaceous-edge or interior traps. In the Ist generation of 1992,
more females were again captured in wooded-edge traps in 2 fields, whereas in the other 2
fields, more were captured in both herbaceous-edge and wooded-edge traps than interior
traps. In the 2nd generation of both years, there was no consistent pattern of distribution of
adult females among sites. The distribution pattern of adult females among fields was not
consistently correlated with the distribution of O. nubilalis larvae or percentage parasitism.
Overall, males were captured than females, and in the Ist generation of both years, more
males were captured near wooded edges of maizefields in which the previous crop had been
maize, than any other sites. Both male and female E. terebrans were captured in malaise traps
at the interface of a woodlot canopy and a maizefield with capture zones from 1 to 4.3 m high.
Dyer and Landis again proposed that E. terebrans distribution in maize fields is influenced
by resources such as sugar and a moderate microclimate present in adjacent woodlots but
unavailable in early-season maize fields (Dyer, Landis, 1997).
This ichneumonid was the dominant parasitoid of O. nubilalis in the sampled fields,
accounting for 92.5% of F1 and 99.2% of F2 parasitism during 1989; and for 92.2% of F1 and
99.1 of F2 parasitism during 1990. Average parasitism by E. terebrans (n = 4 fields) was
63
4.9% and 18.7% of F1, and 10.2% and 9.1% of F2 larvae during 1989 and 1990, resp. The
maximum E. terebrans parasitism observed (37.4%) of the O. nubilalis larvae in 1 field (F1,
1990), is the highest level reported for this species in the Midwest. Parasitism by E. terebrans
during the F1 generation was greater along field margins than in field interiors in most fields
during both years. During 1990, O. nubilalis larvae near wooded edges had significantly
higher E. terebrans parasitism than those near nonwooded edges or field interiors. In the F2
generation, parasitism did not vary significantly from field margins to field interiors in either
year. There was no consistent relationship between O. nubilalis larval density per infested
plant and E. terebrans parasitism. These data suggest that local landscape structure, including
proximity of particular noncrop habitats, plays an important role in the effectiveness of this
natural enemy (Landis, Haas, 1992).
E. terebrans overwinters in larval stage (Baker et al., 1949). After passing winter in the
hibernating catepillar of the corn borer, resumes development in the spring about the time
when the host is preparing to pupate - 22 to 37 days after resumption of development in the
spring. Adults have been observed in the field about the time the young larvae of the host are
abundant in the flowers of the maize. First generation emergence of wasps is in synchrony
with the first larval generation of O. nubilalis. Females mate soon after emergence
(sometimes within an hour) and they are able to lay eggs one day after eclosion (Baker et al.,
1949). Females lay their eggs in catepillars in second, third and fourth stage (Anonymous,
1928), and are highly attracted to chemicals in corn borer frass and webbing, and to corn
borer cuticle, larvae, oral secretions, and feces. When exposed to corn borers, they exhibit
ovipositing behavior. E. terebrans is also attracted to maize plants (Wright, 1996). The eggs
are deposited free in the body cavity of the host larva (Baker et al., 1949). Peak activity is in
synchrony with the peak occurrence of its host O. nubilalis (Winnie, Chiang, 1982, cit. Bokor,
Cagáň, 1999). Adult wasps may live 7-10 days under ideal conditions (75-80 °F, and with
access to water and sugar). However, lifespan is greatly reduced and is only 3-4 days when
temperatures are above 90 °F and there are no sugar sources such as flower nectar or aphid
honeydew available. Previous research has suggested that first generation corn borers were
more likely to be parasitized by E. terebrans than second generation larvae, but this may vary
from year to year. Landis and Haas (1992) reported that in most fields during 1989 and 1990
in Michigan, E. terebrans parasitized more first generation corn borers on field edges where
fields bordered wooded areas. This relationship was only seen in fields bordering wooded
areas, and it was not seen at all with second generation corn borers regardless of bordering
vegetation (Landis, Haas, 1992). Additional studies showed that adult wasps die rapidly when
temperatures exceed 90 °F and that wasps require some type of sugar on a daily basis or they
will die. During the first corn borer generation, prior to maize canopy closure, maximum
temperatures in maize fields may often exceed 90 °F, and sources of nectar or honeydew may
be scarce in the middle of maize fields. Wasps are able to survive better in wooded field
borders, where there is more shade and often flowering plants or sources of aphid honeydew.
First generation O. nubilalis larvae near wooded edges were parasitized at two to three times
the rate of those in field interiors. Adults are not known to feed on hosts (Wright, 1996).
In USA the bionomy of E. terebrans is similar to bionomy of S. turionus. First stage larvae of
the parasite have been found early in July and cocoons are present from the middle to the end
of July or the in middle of August, according to local conditions. In the region of Bergamo, in
the north part of Italy where E. terebrans and S. turionus both attack O. nubilalis the larvae of
E. terebrans issue from the first generation host to pupate and emerge as adult some time
before those of S. turionus, whereas in the hibernating generation this order is reserved, the S.
turionus emerging before the E. terebrans. The summer issuing adults oviposit in the
catepillars of the second generation, in which the parasites hibernate as first stage larvae
(Anonymous, 1928).
64
E. terebrans a parasitoid of the O. nubilalis, was studied at four locations in central Europe
during 1993-1995. Regular parasitism of O. nubilalis was found only at Blatnice in Moravia
(eastern part of the Czech Republic). At this location, the parasitism was 2.22% in 1993,
0.47% in 1994 and 0.06% in 1995. In 1994 and 1995, low parasitism (0.56% and 0.12%,
respectively) was found at Kral'ovsky Chlmec (eastern Slovakia). The records were the first
from the Czech Republic and Slovakia. The parasitoid was not found at Nitra (south-western
Slovakia) and Wroclaw (south-western Poland). The first cocoons of E. terebrans developed
in the first half of June. Parasitoid adults emerged from mid-June to mid-July. E. terebrans is
very rare in relatively warm areas of south – western part of Slovakia, but was regularly foud
in a very cold maize growing region in the eastern Czech Republic (Bokor, Cagáň, 1999). The
literature sourses point that E. terebrans has a number of the other hosts apart from O.
nubilalis. In Japan it is Sesamia inferens (Nagatomi, 1972), in China Chilo suppressalis (She,
He, 1988), Ostrinia furnacalis (Yin et al., 1986), Paranthrene tabaniformis (Georgiev, 2001)
and Saperda populnea (Ling et al., 1997) in Bulgaria Paranthrene tabaniformis (Georgiev,
Tsankov, 1995) and in Italy Zeuzera pyrina (Campadelli, 1996).
2.6.4. Microgaster tibialis Nees
Order: Hymenoptera
Family: Braconidae
Common name braconids, antennae apparently with 16 or more segments, hind trochanters 2segmented, one or no recurrent veins, usually black or brown; some common species with
reddish markings, females often with long ovipositors. The abdomen is about as long as the
head and thorax combined. They are usually more stout-bodied than the similar
ichneumonids. Braconids are parasitoids of caterpillars, sawflies and various beetles. Many
species have been valuable in controlling insect pests. Some larvae are internal parasitoids
while others are attached to the outside of the host's body and feed through the host cuticle.
Some braconids pupate in silken cocoons attached to the outside of the host body, others spin
silken cocoons entirely separate from the host. Braconids are distinguished from ichneumons
by a small difference in the venation of the front wing Braconidae are separated from those in
Ichneumonidae by having none or just one recurrent vein rather than two. It is a large group
with many life histories adapted to parasitizing hosts as diverse as aphids, bark beetles, and
foliage-feeding caterpillars. Many species are egg-larval parasitoids, laying eggs within host
eggs and then not developing until the host is in the larval stage (Foltz, 1998).
M. tibialis Nees, 1834 is a larval parasitoid of O. nubilalis. In Europe, it has been recorded in
north France (Thompson, Parker, 1925; Vance, 1932), north Spain, south Germany (Kunike,
1930; Reh, 1985), Italy (Thompson, Parker, 1928) and Romania (Ciurdarescu, 1984). The
parasitoid was also found in Georgia (former Soviet Union) (Chao You-Shin, 1960), Japan
and China (Cartwright, 1933; Clark, 1934; cit. Bokor, Cagáň, 1999). During 1920-1940, M.
tibialis cocoons were introduced to the U.S.A. from Europe and China (Jones, 1924, 1927;
Baker et al., 1949, cit. Bokor, Cagáň, 1999), however the attempt to establish the parasitoid
was not succesful. In 1950, parasitoid adults were relased in Iowa, but no cocoons were found
in autumn (Blickenstaff et al., 1953, cit. Bokor, Cagáň, 1999). M. tibialis was not recovered
in later survays in North America (Arbuthnot, 1955; Wressel, 1973; Hill et al., 1978; Romig
et al., 1985; Mason et al., 1984, cit. Bokor, Cagáň, 1999).
M. tibialis is polyphagous parasitoid, which is able, exept O. nubilalis, to attack another
species of insect (Vance, 1932; Baker et al., 1949), 14 spacies of Lepidoptera have been
recorded as a host (Thompson, Parker, 1928). The extremely polyphagous habits of this
braconid may also help to reduce its efficiency as a parasite of the borer and meterological
65
conditions seem to have importance in the connection with the attack of M. tibialis on O.
nubilalis in maize, but wheter these conditions operate directly or through the medium of
other factors is at present unknown. Secondary parasites of several species not infrequently
attack the cocoons, especially in Arthemisia (Anonymous, 1928).
Parasitoid ovewinters - hibernates in the stage of prepupa inside very stiff spun cocoon
(Thomson, Parker, 1928; Vance, 1932; Baker et al., 1949; Anonymous, 1928). In Slovakia
and Germany parasitoid adults emerged during April (Bokor, Cagáň, 1999; Zwölfer, 1928),
in the north part of France at the end of April or at the beginning of May, in Germany in
April and the males are first (Zwölfer, 1928), (Thomson, Parker, 1928; Anonymous, 1928).
From the time the parasite issues to the period when young larvae of the host are available on
the Arthemisia plants a considerable period elapses, comprising over two months. It is
possible that an intermediate generation occurs in some other host, before the attack upon the
borer (Anonymous, 1928). According to Baker et al., (1949) the adults appear very early in
the spring, long before their hosts are available in the field, apparently constitutes a
disadvantage to the parasite in areas where alternate hosts, by means of which the intervening
period may be broidged, are absent (Baker et al., 1949). In Germany, O. nibilalis are
parasitized from late July to early August at which time they are still boring in the tassel stalk
of corn plant. Here the larvae are most easily accessible for the parasite, whose ovipositor is
only 2 mm (Zwőlfer, 1928). Females lay their eggs into the body of larva in the second or
third stage (Thomson, Parker, 1928; Vance, 1932; Baker et al., 1949; Gibson, 1927). Usually
only one egg is deposited in larva of O. nubilalis, but sometimes several eggs are deposited,
but there is only one adult larva which is able to finish the life cycle inside the body of the
host (Vance, 1932; Gibson, 1927; Anonymous, 1928). During the whole period of embryonic
and larval development the parasite floats freely in the body cavity of the host (Anonymous,
1928). Young larva hatches after two or three days and passes through three stages within the
host, before emerges and spins cocoon (Vance, 1932). Larva completes its development in the
fifth stage, from this it emerges to spin up in the burrow of the host beside the empty skin,
which is usually found attached to the parasite cocoon (Anonymous, 1928). Prior to pupation,
larva feeds externally on the host for a short time (Vance, 1932). The host continues to feed
normally until the parasite larva gradually weakens it. Death does not, as arule, ensue until
about two weeks after the egg is depositied (Gibson, 1927). The parasite kills the host in the
late fourth instar or the early fifth. This species, like several others, synchronizes its
development with that of its host and has as many generations in a given area as the corn
borer. In USA the development of the parasite larva is completed late in September or early
October. At that time larva leaves host larvae, and spin own white cocoon, measuring 5 mm in
lenght and 2 mm in widht, in the tunnels beside the remains of the dead O. nubilalis
(Anonymous, U.S. Dept. of Agriculture).
The highest level of parazitism of O. nubilalis with M. tbialis in Slovakia and Czech republic
was recorded at Blatnice –1.83% (1995) to 2.95% (1993). Very low parasitism was found at
Nitra. Out of thousands of corn borer larvae collected at this locality only two parasitoid
cocoons were found in 1994. During the investigation period only one parasitoid cocoon was
found at Kráľovský Chlmec (1995) and two cocoons at Wroclaw. M. tibialis cocoons were
obtained from the material collected at Blatnice on 28 September 1993 and 21 October 1994.
After these dates no parasitoid cocoons were gained indicating that all parasitoid cocoons had
developed by the date of collection. In 1995, O. nubilalis larvae were collected twice at
Blatnice 19 September ad 8 November Two parasitoid cocoons were found on 19 September
and two cocoons developed by 22 and 25 September. No parasitoids were gained from corn
borer larvae found on 8 November. In 1994, the first adult emerged on 2 April and the last
one on 15 April 1995, all parasitoid adults emerged between 17-23 April to 3 May. Two
66
adults originating from Wroclaw emerged on 30 March, 1994. One adult originating from
south -west Slovakia emerged on 11 April, 1995 (Bokor, Cagáň, 1999).
2.6.5. Macrocentrus grandii Goidanich
Order: Hymenoptera
Family: Braconidae
This polyembryonic braconid, was one of 26 parasitoids introduced into North America in
1926 from Europe and the Asia where was native (Mahr, 1999), as a part of a program to
reduce corn borer populations (Andreadis, 1982; Baker et al., 1949). When importation began,
little was known about the specific climatic requirements of M. grandii exept that it
flourishedin a variety of conditions ranging from continental climates to regions with warm
winters and hot summers accompanied by excessive rainfall (Parker, 1931). This parasitoid
became established in Illinois during the late 1940’s and was soon considered an important
factor of the corn borer. The importance of M. grandii declined during the early 1960’s,
coincident with the establishment of N. pyrausta throughout to play a minor role as a
mortality factor of the corn borer in Illinois, and M. grandii is curently thought to play a
minor role as a mortality factor of the corn borer in Illinois (J. V. M., unpublished data, cit.
Siegel et al., 1987). This confirmed Mahr (1999), M. grandii was considered a minor
mortality factor of O. nubilalis in the Midwest (USA) although it may be locally abundant at
least in some areas, where it can have a significant impact on borer populations (Mahr, 1999).
According to Mahr (1999) this wasp was first released in Massachusetts and became the
dominant parasitoid in the east over Lydella thompsoni and Eriborus terebrans, the two other
species that became established. In the east parasitization by M. grandii at that time was up to
56%, but much lower in other areas (Mahr, 1999). This parasitoid has several attributes of a
promising biological control agent. It is a specialist on O. nubilalis, its life cycle is well
synchronized with that of its host (Winnie, Chiang, 1984, cit. Udayagiri, Jones, 1993). It is
polyembryonic and has no hyperparasitoids. Consequently, between 1926 and 1949, mass
releases of the parasitoid were made in several north eastern and mid western areas of USA
(Baker el al., 1949, cit. Udayagiri, Jones, 1993). M. grandii was originally released for control
of O. nubilalis in maize. The host, which is polyphagous, has spread to several habitats but M.
grandii continues to be reported only from maize habitats, and the basis for this is unknown.
Olfaction plays an important role in searching behavior of several parasitoids and could be a
factor affecting host-habitat location by M. grandii. M. grandii exhibited possitive flight
response to isolated volatiles from maize plants and observed that the responsewas enhanced
after females were provided oviposition experience. An understanding of M. grandii’s flight
responses to other food plants of its host may provide insights into habitat-location behaviour
in the parasitoid (Udayagiri, Jones, 1993). Several species of flowering plants have possitive
effects on longevity of M. grandii. Plant species with short corollas have some positive effect,
and those with no corolla have the greatest effect in increasing longevity of M. grandii (Orr,
Pleasants, 1992). M. grandii was established in several U. S. regions (Clusen, 1956; Peairs,
Lilly, 1975; Lewis, 1982; cit. Udayagiri, Jones, 1992). Parasitism levels in maize have been
low. According to (Parker, 1931; cit. Udayagiri, Jones, 1992), the inefficiency of this
parasitoid is due to limited ability of the female to locate corn borers. O. nubilalis is
polyphagous but M. grandii locates it only in certain habitats. In an earlier study
(Udayagiri,1991; cit. Udayagiri, Jones, 1992), M. grandii exhibited different olfactory
responses to food plants of its host. It was attarcted to volatiles of maize, potato and snap bean
but not to those of pepper and soybean. It may be possible to increase searching behavior of
female M. grandii by providing chemical stimuli attractive to the parasitoid. If specific
67
volatile plant compounds critical for attraction are identified and synthesized, they might be
used for increasing host-location efficiency of M. grandii. It may also be possible to use plant
synomones for introducing M. grandii to less attractive habitats (Udayagiri, Jones, 1992).
Onstand et al., (1991) collected corn borer larvae from maize fields in Illinois to determine
how host density and other factors influence the distribution of M. grandii parasitism. The
proportion of parasitized larvae was not density dependent at the single-stalk and field scales.
Parasitism was always higher in the first generation of the bivoltine population. Proportion of
parasitized larvae was correlated with the proportion of stalks that had at least one parasitized
larva and with the frequency of infested stalks. These correlations indicated that searching and
oviposition by the female parasitoid may be random among maize stalks (Onstand et al.,
1991). Olson et al., (2000) compared lifetime patterns of carbohydrate and lipid metabolism
in starved and sucrose-fed adults of the parasitoid M. grandii. As expected, sucrose-fed
individuals lived longer than did starved individuals. M. grandii males and females eclosed
with levels of simple storage sugars (presumably primarily trehalose) and glycogen that were
below maximum levels recorded from sucrose-fed parasitoids. Both of these nutrients
dropped to very low levels in starved individuals within 4 days post-emergence and were
maintained at high levels in sucrose-fed individuals throughout their lives. Lipid reserves at
emergence represented the highest lipid levels for both sexes in the two diet treatments, with
levels declining over the lifetimes of males and females from both diet treatments. Olson et
al., (2000) suggest that dietary sucrose is used to synthesize trehalose and glycogen, but not
lipids in M. grandii. Also, in contrast to the patterns observed for the simple sugars and
glycogen, lipid levels in starved individuals did not drop below levels observed in sugar-fed
individuals. The average number of mature eggs carried by females at emergence was 33 and
increased to approximately 85 in sucrose-fed and 130 in starved females by the age of 5 days
in the absence of hosts. The egg maturation rate was therefore higher in starved than in sugarfed females (Olson et al., 2000). Studies on the parasites of O. nubilalis on maize in southcentral Minnesota showed that M. grandii) and E. terebrans overwintered in full fed host
larvae, completing their development and emerging as adults at the same time as the host
adults. The peak abundance of the parasites thus coincided with that of the host. Both
parasites had a 2nd generation, as does O. nubilalis in Minnesota, but only M. grandii was
fully synchronised with the peak abundance of the 2nd host generation (Winnie, Chiang,
1982). This confirmed Parker’s study (1931), who reporetd that 6 to 10 individual M. grandii
normally develop from oviposited egg and that, in case of multiple ovipositions, many larvae
are destroyed before completing their development. Observations on the number of M.
grandii succesfully emerging from each host, then, would seem to indicate that in nature , the
majority of parasitized borers receives three or more eggs (Parker, 1931). The compound
(3R‫٭‬, 5S‫٭‬, 6R‫ )٭‬-3,5-dimethyl-6-(methylethyl)-3,4,5,6, tetrahydropyran-2-one was identified
as a sex pheromone component of M. garndii. This elicits flight initation, upwind anemotaxis,
and casting in male wasps. The compound acts synergistically with (Z)-4-tridecental, a
previously identified sex pheromone component of female M. grandii, to increase male
response to the aldehyde component. The source of the lactone was determined to be the
mandibular glands of male and female wasps. At eclosion a majority of male-female and
female-only cocoon released the lactone and attracted male wasps. Male-only cocoon masse
were not attractive at eclosion and the lactone component was either not released or released
at below-treshold concentration. Mating was observed to occur following eclosion in
laboratory and field studies (Swedenborg et al., 1993; Shyu, 1981; Wishart, 1946). Olfactory
tests demostrated that female and male M. grandii are attracted to allelochemicals
(kairomones, synomones) from both their host, O. nubilalis, and its host, the maize plant. Cut
maize stems were the most attractive to female M. grandii, but females also were attracted to
frass, larvae, feces, and the oral secretion of host larvar reared on maize. When O. nubilalis
68
were reared on artificial diet, the same components were attractive to female wasps, exept that
larval frass repelled. When M. grandii females contacted frass, feces, oral secretions, silk,
larval cuticle, or uxuviae from larval reared on maize or artificial diet, behavior changes
(antennal palpation /antenation/, ovipositor unsheathing and ovipositor probing) occured
exept when frass from larvae reared on maize or artificial diet was contacted. M. grandii
females also antennated maize plant upon contactand a few unsheathed their ovipositor and
probed the damaged area. These behaviors were also elicited when M. grandii females
contacted a substrate in the presence of volatiles from frass, oral secretion, or cut maize plants
(Ding, Swedenborg, Jones, 1989). Considering that M. grandii females have been observed to
repeatedly oviposit in the same larval ECB for 1 h or more (Parker, 1931). After a 3 day
preoviposition period, the female deposits her eggs singly in second or third instar corn borer
larvae. Larval tunnels with frass and webbing are very attractive to the wasps. The female
raises the end of her abdomen, and probes rapidly in the area where the borer has been
feeding. The ovipositor is then inserted through the plant material into the borer, with the
sheath around the ovipositor forming a loop upwards and backwards. Females deposit 200300 eggs. Each egg develops into 15-25 embryos (polyembryony) (Mahr, 1999). According
to(Wishart, 1946, cit. Dittrick, Chiang, 1982), M. grandii is able to oviposit in any of the five
larval instars of the O. nubilalis and produce, throug polyembryony, an average of 25-26
wasps from one host. It has four larval instars, the first three feeding internallly and the fourth
emerging at host ecdysis to feed on the remaining host tissues externally (Parker, 1931, cit.
Dittrick, Chiang, 1982). In first generation corn borers the eggs hatch within a few days, but
in second generation borers they remain unhatched in the overwintering host larva until the
following spring. The larvae in overwintering borers hatch in early April and feed internally
through 3 instars. Immediately after the third molt, the parasite larvae emerge from the body
of their host through the skin and feed externally until the borer is emptied. Glossy light
brown silk cocoons are constructed in an elongate group, to form a 1 inch long cigar-shaped
mass. The cocoon group is attached to the shriveled remains of the host. The adults emerge in
about 10 days, in late June and July to parasitize the next generation of O. nubilalis (Mahr,
1999). Parasitoid emergence occurs only after the host larva reaches maturity in the fifth
instar. After feeding, each larva spins its own coccon, collectivelly forming a cocoon mass
alongside the host. The larvae pupate within the cocoons, and all adults emerge
simultaneously some days later. The immature stage of the parasitoid can be divided roughly
into two parts - an internal phase and an external phase. The internal phase includes the
events of embriogenesis (polyembryonony), hatcing, and larval development trough the third
instar. The external phase includes the emergence of the fourth instar, external feeding on the
host, cocoon formation, pupal development and eclosion (Dittrick, Chiang, 1982). As a
polyembryonic parasitoid, M. grandii has the ability to produce more than one offspring per
egg deposited in the host. This atribute has the potential of increasing the insect´s
reproduction, altouhg Clausen points out that polyembryony is usually coupled wit lower
oviposition (Claucen, 1940, cit. Dittrick, Chiang, 1982).
2.6.6. Bracon hebetor Say
Order: Hymenoptera
Family: Braconidae
Names used for this wasp have been changed from Rhogas kitcheneri to Microbracon
brevicornis, to Bracon brevicornis (Temerak, 1981). B. hebetor was also named Habrobracon
juglandis (Ashmead), Habrobracon hebetor (Say), Microbracon hebetor (Say); common
name The meal–moth parasitic wasp. In the 1970’s, a parasitoid identified as B. hebetor was
69
released for control of Heliothis/Helicoverpa spp. (Lepidoptera: Noctuidae) on the island of
Barbados. Because life-history traits of this parasitoid differed from those reported forB.
hebetor from the United States, Heimpel et al., (1997) conducted a series of laboratory
experiments to determine whether this parasitoid was a population of B. hebetor that attacks
noctuids in the field or a different species from B. hebetor. Heimpel confirmed that Heliothis
virescens was a more suitable host for the Barbados strain than for B. hebetor. However, a
stored-grain infesting pyralid, Plodia interpunctella (Hübner), was a more suitable host for
the Barbados strain than was H. virescens. Reciprocal crosses between the Barbados strain
and B. hebetor showed that the two populations were reproductively isolated. No mating was
observed during a series of 30-min observations of reciprocal crosses, and the crosses
produced only male offspring. Examination of each female’s spermatheca confirmed that
females were not fertilized (Heimpel et al., 1997). This minute wasp occurs naturally
throughout the world associated with stored product moths. (Baker, 2000). B. hebetor is a
gregarious parasitoid that attacks a variety of important lepidopterous pests of stored product
and in the field (Panagiotis, 2005). According to Beard ((1952), cit. Piek, 1966) these wasp
paralyse their victims, larvae of genera Plodia, Anagasta, Galleria; ectoparasitic upon the
larvae Anagasta kuehniella Zeller (Petters, Grosch, 1977). Temerak (1984) in his study
evaluated the sensitivity and suitability of five host species (Galleria mellonella, Ephestia
cautella, Sesamia creatica, Spodoptera littoralis and O. nubilalis) However, the heart and gut
muscles of the paralysed larvae continue to function. The venom is transported by
haemolymph. According to Beard’s calculation, a concentration of 0.05 ppm in the
haemolymph is sufficient to produce a permanent paralysis. Lower concentrations result in
delayed paralysis, reductuction of the percentage of paralysed larvae, and an increased rate of
recovery (Beard, (1952), cit. Piek, 1966). In other insects, for instance larvae of Popillia
japonica and O. nubilalis, the injections of B. hebetor venom are ineffective. Beard did not
find that the effect of the venom was antagonized by haemolymph of O. nubilalis (Piek,
1966). Quinstad et al., (1994) purified three protein toxins from venom of this small parasitic
wasp and the amino acid sequences of 22–31 consecutive residues at the amino-terminus were
determined. These relatively large toxins (apparent molecular mass 73 kDa) were labile under
many isolation techniques, but anion-exchange chromatography allowed purification with
retention of biological activity. Two purified toxins were quite insecticidal (LD50 < 0.3μg/g)
when injected into six species of lepidopterous larvae. On a molar basis, one toxin (Brh-I) has
the highest known biocidal activity against H. virescens (LD50 = 2 pmol/g) (Quinstad et al.,
1994). Host plasma proteins and protein digestion in larval parasitoids were studied by Baker
and Fabrick (2000) during trophic interactions of the ectoparasitoid B. hebetor with a host,
larvae of the Indian meal moth, P. Interpunctella. They could detect no apparent differences
in host hemolymph protein patterns up to 72 h after paralysation and/or parasitization by B.
hebetor. A 190 kDa putative apolipophorin I present in host hemolymph could not be detected
in the midguts of feeding B. hebetor larvae indicating that it is rapidly digested. The major 60
kDa storage proteins (putative hexamerins) in host hemolymph were detected in the parasitoid
midgut and were completely digested 24 h after cessation of feedig and the beginning of
cocoon formation. Host hemolymph had a pH of about 6.4. The pH optima of the midgut
proteinases in the larval parasitoid were in the alkaline region, but midgut fluid in feeding
parasitoid larvae was about pH 6.8. Based on enzyme activity against selected artificial
proteinase substrates including azocasein, N- -benzoyl-L-Arg p-nitroanilide (BApNA),
succinyl-Ala-Ala-Pro-Phe p-nitroanilide (SAAPFpNA), succinyl-Ala-Ala-Pro-Leu pnitroanilide (SAAPLpNA), and inhibition by selected proteinase inhibitors, serine proteinases
appear to be the predominant class of enzymes involved in protein digestion in the midguts of
B. hebetor. There is also an active aminopeptidase (LpNA) associated with the microsomal
fraction of midgut preparations. There was no evidence for preoral digestion or ingestion of
70
proteinases from host hemolymph by the parasitoid larva. There was a very active BApNAase
in the soluble fraction of midgut extracts. This activity increased on a per midgut basis up to
24 h after the beginning of cocoon formation but decreased rapidly by 48 h. Two major (P1
and P3) and several minor proteinases were detected in midgut extracts of B. hebetor analysed
with gelatin zymograms. The apparent molecular mass of P1 varied from 95 to 49 kDa
depending on protein loading. P3 had an apparent molecular mass of 39 kDa that was
independent of protein loading. In summary, electrophoretic evidence indicates that host
hemolymph protein patterns do not change significantly for at least 72 h after paralysation by
B. hebetor. The role, if any, of envenomization in preventing breakdown of hemolymph
proteins during this time remains to be determined. Because the predominant host hemolymph
proteins, a putative apolipophorin and the putative hexamerins, are readily digested by the
serine proteinases present in the midguts of this parasitoid larva, these or similar proteins
would provide an easily digested source of dietary amino acids that could be used for
development of artificial diets for this beneficial insect (Baker, Fabrick, 2000). B. hebetor is a
minute parasitic wasp that preys exclusively on Indian meal moth larva, flour moths, and
almond moth caterpillars external to grain. It is probably more suited to large bulk storage
facilities where large numbers of moths are present to provide the wasp with ample food and
breeding sources (Baker, 2000). Darvish et al., (2003) investigated a direct behavioral assay
to investigate the preferred habitat for host searching by the B. hebetor. The effects of mating,
feeding and post-emergence experience on female parasitoid choices of searching sites were
also examined. B. hebetor appears to be directed to the habitat of its host through chemical
cues originating from the host larvae, frass and adults. These cues elicit a series of directed
responses by the female. Generally, the data showed that flour containing 30-day-old larvae
was preferred by B. hebetor females. This was followed by the flour containing the frass, then
the adult host, and finally the flour containing 10-day-old larvae. It appears that cues
produced by young larvae were the weakest whereas cues produced by older ones were the
strongest. Feeding seemed to be important in the location of the proper searching site.
Although the cues were normally learned by the immature stages of the parasitoid, and were
subsequently manifested in their responses as adults, adult experience increased the ability of
the parasitoid to locate the suitable habitat for searching (Darvish et al., 2003). Panagiotis
(2005) in his tests studied the effect of host species, size and larval competition on parasitoid
size, survival and development. In laboratory studies, wasp eggs at a range of densities, were
placed on larvae of different weight of three Lepidoptera host species namely Adoxophyes
orana (Fischer von Röslerstamm, Tortricidae), P. interpunctella and Lobesia botrana (Dennis
& Schiffermueller, Tortricidae). On A. orana survival of immature parasitoids was very low
at all densities and different host weights. On L. botrana survival progressively reduced as
egg density increased at both host weights examined for this host. Survival on P.
interpunctella was significantly affected by egg density but not by host weight. Initial egg
density had a significant effect on the size of emerging adults from each rearing host. Smaller
adult parasitoids emerged as egg density per larva increased. Larval host weight of P.
interpunctella and A. orana had a significant effect on the size of emerging adult parasitoids
mainly at the higher egg densities used in these experiments (Panagiotis, 2005). Demography
of B. hebetor on two pyralid host species Galleria mellonella and Ephestia kuehniella was
studied by Masood and Hsin (2006) at 28 °C in the laboratory. Observed data were analyzed
based on an age-stage, two-sex life table, to take both sexes and variable development into
consideration. The intrinsic rate of increase (r), finite rate of increase (λ), net reproductive rate
(R 0), gross reproductive rate (GRR), and mean generation time (T) of B. hebetor on G.
mellonella were 0.1520 d−1, 1.1640 d−1, 12.5 offspring, 50.1 offspring, and 16.8 d,
respectively. These values were not significantly different from the values obtained for E.
kuehniella, i.e., 0.1375 d−1, 1.1473 d−1, 11.9 offspring, 54.9 offspring, and 18.2 d. The life
71
expectancy of an B. hebetor egg was 10.6 d on E. kuehniella and 10.4 d on G. mellonella. On
both host species, the maximum reproductive value of female B. hebetor occurred on the 12th
day (Masood, Hsin, 2006). Perez-Mendoza et al., (2000) investigated biochemical
mechanisms of malathion resistance in a malathion-resistant strain of the parasitoid B. hebetor
collected from a farm storage in Kansas. General esterase activities were significantly lower
in the resistant strain compared with those in a susceptible strain. However, no significant
differences were found in activities of malathion specific carboxylesterase (MCE), glutathione
S-transferase and cytochrome P450 dependent O-demethylase activities, cytochrome P450
contents, and sensitivity of acetylcholinesterase to inhibition by malaoxon between the 2
strains. Because MCE was not elevated in the resistant strain, the weak malathion resistance
in B. hebetor may result from a different mechanism compared with that hypothesized for
some insect species in which reduced general esterase activity is accompanied by an elevated
MCE. Decreased esterase activity in the resistant strain suggested that null alleles of some
esterases were associated with the resistance. Indeed, E1 and E2, major esterases in the
susceptible strain, were not present in the resistant strain on polyacrylamide gels that were
stained for esterase activity using the model substrate 1-naphthyl acetate. In contrast, the
activity of esterase E3 on the gels was much higher in the resistant strain as compared with
that of the susceptible strain. These findings indicate that malathion resistance in B. hebetor is
associated with both an increased activity of the esterase E3 and null alleles of the esterases
E1 and E2 (Perez-Mendoza et al., 2000). According to Petters et al., (1983) the adult of wasp
B. hebetor are sensitive to the soluble organic fraction (SOF) of diesel particulate emissions
tested for their physiological and genotoxic effects. Adult female survival after topical
treatment was significantly decreased at the higher concentrations of SOF. Daily egg
production, a sensitive assay for genotoxic and physiological effects, was not significantly
affected at any concentration. Egg hatch ability on Days 1-5, representing vitellogenic oocytes
at the time of treatment, was decreased, but this effect lacked consistency and dose
dependence. An extensive dominant lethal test was performed with negative results (Petters et
al., 1983). Zaki et al., (1998) observed the kairomonal effect of hexane extract of the larvae
of O. nubilalis and Sesamia cretica on B. hebetor adults through olfactometer tests. The
parasitoid males showed no definite response to any kairomone. Females were attracted to the
kairomone of S. cretica more than to that of O. nubilalis. Highly significant effect of the sex
pheromone of O. nubilalis on the females of B. brevicornis was recorded. Kairomones
(hexane extracts of larvae) varied in their effect on the released B. hebetor parasitoids. The
kairomone of S. cretica increased the parasitisation from 7.74 to 17.05%, while the
kairomones of O. nubilalis and of Spodoptera littoralis were not significantly effective.
Spraying molasses solution (10%) on the maize stalks before releasing B. hebetor parasitoids
increased the rate of parasitism from 7.74 to 28.21%. The concentration of 5% gave
insignificant increase in the parasitisation rate (Zaki et al., 1998). Holloway et al., (2000)
tested whether sex determination in the parasitic wasp Bracon sp, near hebetor is based upon
a single locus or multiple loci. Holloway constructed linkage map using random amplified
polymorphic DNA (RAPD) markers. The map includes 71 RAPD markers and one
phenotypic marker, blonde. Sex was scored in a manner consistent with segregation of a
single "sex locus" under complementary ses determination (CSD), which is common in
haplodiploid Hymenoptera. Under haplodiploidy, males arise from unfertilized haploid eggs
and females develop from fertilized diploid eggs. With CSD, females are heterozygous at the
sex locus; diploids that are homozygous at the sex locus become diploid males, which are
usually inviable or sterile. Ten linkage groups were formed at a minimum LOD of 3.0, with
one small linkage group that included the sex locus. To locate other putative quantitative trait
loci (QTL) for sex determination, sex was also treated as a binary threshold character. Several
QTL were found after conducting permutation tests on the data, including one on linkage
72
group that corresponds to the major sex locus. One other QTL of smaller effect had a
segregation pattern opposite to that expected under CSD, while another putative QTL showed
a female-specific pattern consistent with either a sex-differentiating gene or a sex-specific
deleterious mutation. Comparisons are made between this study and the in-depth studies on
sex determination and sex differentiation in the closely related B. Hebetor (Holloway et al.,
2000). B. hebetor has CSD and displays mating behaviours that lessen CSD load, including
mating at aggregations of males and inbreeding avoidance by females. To examine the
influence of population structure and the mating system on CSD load, Antolin et al., (2003)
conducted genetic analyses of an B. hebetor population in Wisconsin. Given the frequency of
diploid males, they estimated that the population harboured 10-16 sex-determining alleles.
Overall, marker allele frequencies did not differ between subpopulations, but frequencies
changed dramatically between years. This reduced estimates of effective size of
subpopulations to only N3 approximately 20-50, which probably reflected annual fluctuations
of abundance of B. hebetor. They also determined that the mating system is effectively
monogamous. Models relating sex-determining allele diversity and the mating system to
female productivity showed that inbreeding avoidance always decreased CSD loads, but
multiple mating only reduced loads in populations with fewer than five sex-determining
alleles. Populations with N3 less than 100 should have fewer sex-determining alleles than
they found, but high diversity could be maintained by a combination of frequency-dependent
selection and gene flow between populations (Antolin et al., 2003). This parasitic wasp
suffers severe inbreeding depression. Ode et al., (1995) in his study examined two
behavioural mechanisms that minimize mating between close relatives. First, the majority of
males and females were unwilling to mate immediately upon emergence. Receptivity to
mating slowly increased with age of the adult. By the time most individuals were willing to
mate, the majority of wasps had dispersed from the natal site. Second, females tended to avoid
mating with brood-mates when given a choice between a male that developed on the same
host and one that developed on a different host. Experiments using eye-colour mutants and
broods composed of relatives and non-relatives indicated that females discriminated against
male brood-mates on the basis of environmental cues. Females consistently mated with
brothers and non-brothers if they developed on another host, but tended to reject brothers and
non-brothers from the same brood as themselves. Females maintained the ability to recognize
brood-mates for at least 5 days after eclosion (Ode et al., 1995). Females of this tiny
parasitoid paralyze and lay eggs in late instar moth larvae. Each female produces about 100
eggs. One to eight larvae develop per host (Baker, 2000). Females wasp of this parasitoid with
fewer than 4 ovarioles (1, 2 or 3) produce proportionaly fewer eggs than their “normal” 4ovariole sisters. In Females with 5-9 ovarioles, egg production did not increase significantly
(Petters, Grosch, 1977). Ryoo et al., (2003) studied egg dispersion and the sex ratio of
progeny in relation to the host density of the parasitoid, B. hebetor infesting larvae of P.
interpunctella. Females appeared to allocate eggs in relation to host density to avoid laying
more eggs than could complete development on a host. The dispersion pattern of the
parasitoid ovipositions among hosts was influenced by host density. Multiple visitations and
ovipositions by females on hosts caused a highly aggregated pattern at low-host densities.
Hatch rate of eggs decreased as the number of eggs on a host increased. Females seemed to
regulate progeny sex ratio (male/total) based on the number of eggs on the hosts and the
clutch size of the hosts they encountered. However, the overall progeny sex ratio remained at
approximately 0.5 regardless of host density, probably because the allocation of eggs was
related to host density (Yu et al., 2003). Egg to adult takes 9 to 10 days (30 °C). Adult female
longevity about 23 days. From parasitism to adult emergence averages from 10 to 13 days
(Baker, 2000). The body color of B. hebetor adults reared on E. cautella larvae was either
black, yellow with black spots, or completely yellow when development from egg to adult
73
took place at 15–18 °C, 25 or 35 °C, respectively, and the wasps were. The longest adult lifespan of both sexes occurred when adults reared and emerged at 25 °C were held at 15–18 °C.
Female adults of all colors lived longer than males, especially at 25 and 35 °C. The lowest
parasitizing efficiency was at 35 °C, whereas the highest number of eggs per female occurred
at 25 °C irrespective of the body color. In general, the parasitoid wasps have somewhat
tolerated the three temperature levels determined by Ahmed et al., (1985) and continued to
reproduce in spite of their distinct variations in body color (Ahmed et al., 1985).
The biology of this parasitoid was studied when reared on seven different artificial diets (in
vitro rearing), under controlled temperature (25 +/- 2 degrees C), relative humidity (60 +/10%), and photoperiod (14-h photophase), and compared to its biology on its natural host A.
kuehniella (in vivo rearing). The artificial diet contained 60% holotissue of Diatraea
saccharalis (Fabricius) pupae, 12% fetal bovine serum, 12% lactoalbumin hydrolysate, and
16% egg yolk, enabled development similar to that obtained on the natural host. The life cycle
duration (egg-adult) was not significantly different, and the adults reared on this diet promptly
paralyzed and parasitized the natural host, though at a lower proportion than those reared in
vivo. There was no difference in the longevity of females obtained with these two different
rearing systems (in vivo and in vitro). However, about 60% of the larvae developed on the
diet failed to produce a protective cocoon during the pupal phase, indicating a sub-optimal
quality
associated
with
this
artificial
medium
(Magro,
Parra,
2004).
The B. hebetor wasp is a good biocontrol agent partly because it feeds rapidly and has gut
enzymes that quickly break down two major blood proteins in moth larvae (Baker, 2000).
2.6.7. Sympiesis viridula Thomson
Order: Hymenoptera
Family: Eulophidae
Eulophidae is a large cosmopolitan family with about 328 valid genera and 2972 species
known as of 1993. Over half of the eulophid genera have been described from Australia.
Important morphological characters include antennae inserted below the frons, funicle 3-4
segmented, and the male antenna may be pectinate. The axillae are frequently extended
anteriorly, thus the scapulae is usually incised. Tarsi are 4-segmented. There is a straight
foretibial spur (calcar), darkly colored body and a lightly sclerotized body that warps badly
after death. Although most Eulophidae are primary parasitoids, many develop as
hyperparasitoids and some as facultative hyperparasitoids. Most species are gregarious,
although many solitary species are known. There are both ecto- and endoparasitoids known
in the Eulophidae. There is a wide host range, but the majority of species parasitize larvae of
Lepidoptera. However, representatives of a number of insect orders also are attacked, as are
all host stages. Eulophidae are often encountered as parasitoids of crop pests, and are
considered valuable in natural control, although only few species have been imported for
biological control. Eulophidae have a body that is with or without metallic luster, usually
lightly sclerotized (often collapsed or shriveled when dry). The antennae have 5-10 flagellar
segments; females usually with a funicle of 2-4 nonring-like segments and with a club of 3 or
less segments. Male antennae have 6 or fewer distinct flagellar segments, and often without a
distinct club. The prepectus is conspicuous, usually subtriangular. The mesoscutum either
has notauli or they are absent. The scutellum sometimes has a pair of submedian longitudinal
lines and/or 1-3 pairs of long paralateral setae. The axillae are often partly advanced anterior
to the scutellum. Individuals usually are fully winged. The protibial spur is short, straight,
simple. The tarsi have 4 tarsomeres. The mesosoma and metasoma are separated by a
distinct constriction. The petiole is transverse to elongated. Eulophidae is one of the largest
74
chalcidoid families with ca. 540 nominal genera and 3,900 nominal species. Infrafamily
classification is unstable, but 4 subfamilies are generally recognized, as will be discussed
below. Eulophidae is one of the most important chalcidoid families economically speaking.
Most species are primary parasitoids of concealed larvae, especially leafmining Lepidoptera,
Diptera, Hymenoptera, and Coleoptera; but the host range is extremely diverse. Some are
phytophagous (description and statics).
S. viridula in literature also named as Eulophus viridulus for which no host records have been
found in the literature prior to 1928, was first citated as a parasite of O. nubilalis under the
name Eulophus sp., and was later mentioned as Hemiptarsenus unguicellus Zett (Parker,
Smith, 1933). First record of this parasite being associated with O. nubilalis was made by
Filipjev (1930) who reared two specimens from this host taken in hemp in Italy. Next findings
were observed in France where this chalcid was foud in Arthemisia in O. nubilalis tunnels in
March and August 1923 and 1925. In March 1925 two colonies were found in maize on the
Mediterianean Coast. Oglobin bred a colony of this species from O. nubilalis from maize in
V. Sevejut, Czechoslovakia, in September 1927 (Parker, Smith, 1933). Goidanich (1928) cites
this chalcid as being very common in the region of Bologna, Italy in hemp. S. viridula was
also detected in Hungary, Bulgaria and Romania (Ellinger, Sachtleben 1928), Yugoslavia
(1929), Azerbeijan and Russia (Filipjev, 1930). There are two generation of S. viridula in the
Mediterranean and Plavisian Area in maize, in the mountainous regions in nothern parts of
Yugoslavia is propably one generation in Arthemisia, there are two generations of the chalcid
in Campanian in maize and one complete in hemp, as in Padovian area (Parker, Smith, 1933).
Sachtleben et al., (1930) in the conditions of Hungary pointed that the pupae are found in the
autumn beside dead corn borers and that the imagos emerge in April and May the following
year (Sachtleben et al., 1930). A very low occurrence of S. viridula was observed at some
locations in Slovakia during 1993 – 1995. At Nitra locality in southwestern part of Slovakia
parasitation by S. viridula reached 0.00%, 0.26% and 0.05% and at Kráľovský Chlmec
locality 0.00%, 0.40% and 0.12% (Bokor, Cagáň, 1997). In Slovakia parasitoid pupae were
collected at the end of maize growing season in September and October (Bokor, Cagáň,
1997). S. viridula passes winter in the pupal stage in the O. nubilalis tunnels. Hibernation
seems to be a true diapause.The pupae collected in winter or early spring gave adults under
laboratory conditions in March. In nature the spring emergence occurs in late April or May
(Anonymous, 1928). In Slovakia the first adults emerge during April and May, the maximum
of imagos were observed in the first week of May (Bokor, Cagáň, 1997). In Hungary the
larvae were occurred in July 22, 23 and August 12; pupae on July 7, August 1 and August 4:
eggs on August 7. This chalcid produces at least two generations a year, namely a summer
generation beside the known winter generation (Sachtleben, undated). The adults are rather
strong fliers as compared with many chalcids (Parker, Smith, 1933; Anonymous, 1928). They
can attack some other host or wait around until there are larvae of O. nubilalis. Females
deposits eggs on the ouside of the O. nubilalis larva in the numbers from 5 to 15, the average
being about 10. The period from egg to adult of this chalcid is about 14 days, from hatching to
pupation required 5 days and from pupation to emergence 7 to 9 days (Parker, Smith, 1933).
The resulting larvae feed together externally on the O. nubilalis catepillar, consuming it
almost entirely (Anonymous, 1928). In Czechoslovakia was reared a colony of this parasite to
the adult stage on September (Parker, Smith, 1933). When they are full grown, that is in 8 to
15 days, they pupate on the spot, giving rise to the adults of the next generation in about 15
days depending on the temperature (Anonymous, 1928).
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2.7. Characteristic of microsporidia
Microsporidia are eukaryotic spore forming obligate intracellular protozoan parasites first
recognized over 100 years ago. These organisms infect all of the major animal groups and are
now recognized as opportunistic pathogens of humans. Microsporidian spores are common in
the environment and microsporidia pathogenic to humans have been found in water supplies.
The genera Nosema, Vittaforma, Brachiola, Pleistophora, Encephalitozoon, Enterocytozoon,
Septata (reclassified to Encephalitozoon) and Trachipleistophora have been found in human
infections. These organisms have the smallest known eukaryotic genomes. Microsporidian
ribosomal RNA sequences have proven useful as diagnostic tools as well as for phylogenetic
analysis. Recent phylogenetic analysis suggests that Microsporidia are related to the fungi.
These organisms are defined by the presence of a unique invasion organelle consisting of a
single polar tube that coils around the interior of the spore. All microsporidia exhibit the same
response to stimuli, that is, the polar tube discharges from the anterior pole of the spore in an
explosive reaction. If the polar tube is discharged next to a cell, it can pierce the cell and
transfer its sporoplasm into the cell. A technique was developed for the purification of polar
tube proteins (PTPs) using differential extraction followed by reverse phase HPLC. This
method was used to purify the PTPs from Glugea americanus, Encephalitozoon cuniculi, E.
hellem and E. intestinalis. These PTPs demonstrate conserved characteristics such as
solubility, hydrophobicity, mass, proline content and immunologic epitopes. The major PTP
gene from E. cuniculi and E. hellem has been cloned and expressed in vitro. The gene
sequences support the importance of ER and in the formation of the polar tube as suggested
by morphologic studies. Analysis of the cloned proteins also indicates that secondary
structural characteristics are conserved. These characteristics are probably important in the
function of this protein during the eversion/assembly of the polar tube and in providing
elasticity and resiliency for sporoplasm passage (Weiss, 2001). It was recognized that
microsporidia are related to fungi, but the strong opinion of the participants was that the
International Code of Zoological Nomenclature should continue to be applied for taxonomic
descriptions of the Microsporidia and that they be treated as an independent group emerging
from a paraphyletic fungi. There continues to be exponential growth in the pace and volume
of research on these ubiquitous intracellular protists. The small genomes of these organisms
and the reduction in the size of many of their genes are of interest to many disciplines. Many
microsporidia are dimorphic and the mechanisms underlying these morphologic changes
remain to be elucidated. Epidemiologic studies to clarify the source of human
microsporidiosis and ecologic studies to understand the multifaceted relationship of the
Microsporidia and their hosts are important avenues of investigation. Studies on the
Microsporidia should prove useful to many fields of biologic investigation (Weiss, 2005).
Microsporidia are obligate parasites of most animal phyla, including Arthropoda. This
extremely diverse and parasitic group of organisms was once an order in the phylum
Protozoa, but has been elevated to phylum status (Sprague et al., 1992). The microsporidia
are obligate intracellular parasites which have diverse life cycles involving both horizontal
and vertical transmission and parasitise a wide range of vertebrate and invertebrate hosts
(Dunn, Smith, 2001). All orders of insects contain representative species that are infected by
microsporidia. The phylum Microsporida contains 160 genera, many with complex life cycles
and/or dimorphic spore types and alternate hosts. Most, if not all, species of microsporidia
have a common characteristic; they produce environmentally resistant spores that are
responsible for horizontal transmission. Spores produced by infected hosts are present in the
feces, the silk, or are liberated when an infected host dies. The environmentally resistant
spores, when eaten by a susceptible host, germinate, send a special organelle, called the polar
tube, into an insect’s midgut epithelial cell, inject an infectious sporoplasm and the infection
76
is initiated (Brooks, 1988). Microsporidia also may be transmitted from an infected female to
her offspring either transovarially (inside the egg) or on the egg surface (transovum
transmission). In addition, microsporidia may be transmitted from infected to healthy
individuals via the oviposition of parasitic insects. Unlike the other groups of insect pathogens
(viruses, bacteria, fungi) and also the nematodes, the microsporidia have no serious
contenders for extensive development and commercialization as microbial insecticides.
Nosema locustae is registered as a microbial control agent of grasshoppers, and both Nosema
algerae and Vairimorpha necatrix have been considered as possible candidates for
development as microbial insecticides. Nevertheless, it is very unlikely that N. locustae will
become a major product or that N. algerae or V. necatrix will ever be registered as microbial
insecticides. For this reason, there has been relatively little interest in determining the
environmental persistence of microsporidia relative to their performance as microbial
insecticides. Although microsporidia have little potential as microbial insecticides, they are
very important natural control agents for many species of insects. To promote natural control
systems, it is important to understand how microsporidia persist in nature and how different
environmental factors affect the persistence and, ultimately, the horizontal transmission of
microsporidia. Therefore, most of the research questions about the persistence of
microsporidia in the environment have not been insecticidal questions such as the half-life of
microsporidia on leaf surfaces or the formulation of more stable microsporidian insecticides,
but rather how microsporidia are transmitted from infected hosts to susceptible hosts. During
this transmission process the extracorporeal spores of microsporidia are exposed to many
environmental conditions, and these conditions affect the efficiency of horizontal
transmission. The microsporidia are a very diverse group of organisms and, with the
exception of the direct effects of sunlight, which can quickly kill most microorganisms,
different groups of microsporidia do not respond uniformly to most other types of
environmental stress. In addition, the effects of environmental stress on microsporidian spores
can be determined only by bioassays against susceptible hosts. There are no vital stains that
reliably can determine the infectivity of microsporidian spores, and, since microsporidia are
obligate parasites, infectivity and/or viability cannot be determined by growing microsporidia
on artificial media. Therefore, even though infectivity (can it infect a susceptible host?) and
viability (are the spores alive?) may not technically be the same, since a spore can be alive
and yet be unable to infect, infectivity and viability are indistinguishable as estimates of the
survival of microsporidian spores in the environment. Relatively few species of microsporidia
have been examined for their reaction to environmental stresses, which means that the
generalizations which have been done about how microsporidia respond to environmental
stress maybe modified as the additional groups of microsporidia have been examined. The
persistence of microsporidia is based on their adaptations to the specific environment of their
host and environmental conditions during the horizontal transmission process (Brooks, 1988;
Maddox, 1977; Maddox, 1973). The microsporidia are an ancient and diverse group of
protists which have many unusual characteristics. These include prokaryotic-like 70s
ribosomes, enclosed nuclear division, a lack of mitochondria and complex life cycles which
frequently involve vertical transmission. This use of vertical transmission is unparalleled by
other protists and is seen only among bacterial endosymbionts and sex ratio distorters and in
host cell organelles. Transovarially transmitted microsporidia can have unusual and profound
effects on host population sex ratios (Dunn et al., 2001). According to Terry et al., (2004)
following their initial description of a microsporidian that feminizes its crustacean host, they
survey the diversity and distribution of vertical transmission within the Microspora. They
found that vertically transmitted microsporidia are ubiquitous in the amphipod hosts sampled
and that they are also diverse, with 11 species of microsporidia detected within 16 host
species. They found that infections were more common in females than males, suggesting that
77
host sex-ratio distortion occurs in five out of eight parasite species tested. Phylogenetic
reconstruction demonstrates that vertical transmission occurs in all major lineages of the
phylum Microspora and that sex-ratio distorters were found on multiple branches of the
phylogenetic tree. they propose that vertical transmission is either an ancestral trait or evolves
with peculiar frequency in this phylum. If the association observed here between vertical
transmission and host sex-ratio distortion holds true across other host taxa, these eukaryotic
parasites may join the bacterial endosymbionts in their importance as sex-ratio distorters
(Terry et al., 2004).
2.7.1. Effect of environmental factors
2.7.1.1. Solar radiation / sunlight
Direct sunlight kills the unprotected spores of all species of microsporidia within in a few
hours (Brooks, 1988; Maddox, 1977; Kaya, 1977). The half-life of V. necatrix exposed to
direct sunlight on glass microscope slides was about two hours (Maddox, 1977), and Ignoffo
et al., (1977) reported a half-life of 2.1 hours when they exposed V. necatrix spores on
Helicoverpa zea eggs to radiation from a germicidal lamp (peak radiation at 254 nm). Brooks
(1988) summarized the research results of other workers on the effect of sunlight and
ultraviolet radiation on the spores of nine species of microsporidia. Research methods were
variable, but unprotected spores did not survive exposure for more than a few hours. There
was more variability in the survival of spores between the substrates on which the spores were
exposed than between the different species of microsporidia. It is likely that most species of
microsporidia have similar responses to radiation (Brooks, 1988).
2.7.1.2. Temperature
Most of the studies on the effects of high temperature on microsporidia were conducted in an
attempt to eliminate microsporidian infections from insect colonies. Infected insect hosts as
well as extracorporeal spores have been involved in these studies (Baribeau, Burkhardt, 1970;
Benjakova, Verejskajs, 1958; Hartwig, 1970; Vandermeer, Gochnauer, 1969). Studies on
extracorporeal spores have usually involved dry spores, and, since higher temperatures
usually have a drying effect, it is difficult to distinguish between the drying effect of higher
temperatures and the absolute effect of the higher temperature itself. For most species of
microsporidia, time of survival is inversely proportional to the higher temperature. For
example, Maddox (1977) found that dry V. necatrix spores survived for three weeks at 40 °C
but survived for only five hours at 50 °C and 30 minutes at 60 °C. Kaya (1977) found that V.
necatrix spores survived for 144 hours at 35 °C, suggesting that the moisture provided by the
bean leaf on which the spores were placed reduced the effect of the higher temperature.
Different species of microsporidia respond very differently to low temperatures that are above
freezing. Brooks (1988) and Maddox (1977) have reviewed this subject. Most microsporidia
from terrestrial insects will survive for several years at 2 to 5 °C in sterile water suspensions.
In sterile water suspensions at 2 to 5 °C, Oshima (1964) maintained viable spores of Nosema
bombycis for 10 years and Revell (1960) stored viable spores of Nosema apis for seven years.
If the water suspension contains organic debris and microbial growth occurs in the water
suspension, the spores will not survive for more than a few days (Brooks, 1980; White, 1919).
Some microsporidia from aquatic insects will not survive storage at lower temperatures
(Undeen, Johnson, Becnel, 1993). A similar dichotomy exists between microsporidia from
terrestrial insects and aquatic insects relative to their responses to subfreezing temperatures.
Most microsporidia from terrestrial insects will survive the freezing process, while most
78
species of microsporidia from aquatic hosts will not (Maddox, Solter, 1996). The length of
time spores will remain viable over a range of temperatures while frozen has not been
thoroughly investigated. Spores of many species of microsporidia from terrestrial insect hosts
will survive in a water suspension in liquid nitrogen for more than 20 years and require no
special freezing or thawing rates (Maddox, Solter, 1996), but the addition of cryoprotectants,
such as glycerol, promotes survival of spores in liquid nitrogen. The length of time spores are
reported to survive subfreezing temperatures from 0° to –35 °C ranges from two to 24 months
(Fuxa, Brooks, 1979; Maddox, 1973). In temperate climates spores often must overwinter in
the habitat of their host to initiate infections in the host population in the spring. Therefore, it
is likely that the spores of many species of microsporidia must withstand freezing for several
months if they are to infect hosts successfully early in the spring. Conversely, microsporidia
of aquatic hosts are much less likely to encounter freezing conditions. Ponds and rivers
seldom freeze at the bottom, where the microsporidian spores occur (Maddox, Solter, 1996).
2.7.1.3. Moisture/humidity
As with freezing, the microsporidia of aquatic insects generally are not able to survive
completely dry conditions (Alger, Undeen, 1970; Brooks, 1988). Since freezing has a drying
effect on organisms, the similar responses to these two environmental conditions are not
unexpected. Microsporidia from terrestrial insects exhibit a range of longevity records when
held in a dry conditions with limited exposure to ultraviolet light. Survival times for eight
species of microsporidia held as dry spores over a range of conditions were from two weeks
to more than a year (Maddox, 1973; Kramer, 1970). Spores of microsporidia such as
Octosporea muscaedomesticae, transmitted in fecal deposits, survived six to 12 months.
While drying generally is harmful to most species of microsporidia, the addition of free water
to the dry spores of some microsporidia is equally harmful. Spores of the microsporidium
Nosema whitei, a pathogen of flower beetles, can survive for over a year as dry spores in
flour, but when the spores are placed in water they germinate and extrude their polar filaments
and thus lose their infectivity (Milner, 1972; Maddox, 1973). Kramer (1970) obtained similar
results with the microsporidian O. muscaedomesticae. Dry spores survived on glass
microscope slides for more than one year, but the addition of water to the slide greatly
reduced infectivity, presumably because the water stimulated spore germination (Kramer
(1970).
2.7.1.4. Effect of pH
The pH of the medium encountered by microsporidian spores has a profound influence on the
germination of spores (Frixione et al., 1992; Undeen, 1976). Nevertheless, because other
factors are involved and germination usually requires more than simple exposure to a single
pH medium, it is unlikely that the pH values of water encountered in nature would influence
the spontaneous spore germination of many species of microsporidia. The long-term effects of
pH as an additional variable on survival of microsporidian spores could be important, but has
not thoroughly been examined (Maddox b, undated).
2.7.1.5. Wind
The direct effect of wind on survival of microsporidian spores has not been investigated, but
wind could have an indirect effect in many ways. Fecal pellets from microsporidian-infected
insects often contain many spores, and wind may play an important role in the movement and
redistribution of infected fecal pellets. Where the pellets are distributed will influence which
79
of the above factors contribute to spore survival. Likewise, wind affects the distribution of
infected insects which, in turn, affects the distribution and, ultimately, the survival of spores
(Maddox b, undated).
2.7.1.6. Interactions between above factors
Although some of the above factors can be isolated in laboratory experiments, in nature they
act simultaneously. In addition, each factor does not remain at a constant value. Ultraviolet
radiation and temperature fluctuate greatly over a 24-hour period. The microclimate where
microsporidian spores reside almost always is very different from ambient reported climatic
data. While the survival times reported for spores of different microsporidian species for a
specific factor (at a constant value) give us a "ballpark figure" of survival times, they may not
accurately represent the survival times of spores in nature. Some factors cannot be isolated,
even in laboratory experiments. Solar or ultraviolet radiation produces heat, unavoidably
making the effect of temperature and radiation related (Maddox b, undated). Kaya (1977)
wisely recognized this in his studies on radiation/temperature effects. Likewise, drying of
spores is enhanced by both radiation and high temperatures. There have been few hypothesistesting experiments involving the interactions of detrimental environmental factors on
microsporidian spores (Maddow b, undated).
2.7.1.7. Substrate effects
It is probably restating the obvious to conclude that "any substrate which offers some
protection from direct sunlight and provides a constant source of moisture extends spore
longevity" (Maddox, 1977). This probably is true for all microsporidian species except those,
such as Nosema whitei, that germinate in the presence of water. All studies involving
substrate/radiation interactions concluded that spores on more complex substrates survive
exposures to radiation for longer periods. For example, spores survived exposure to sunlight
for three hours on a glass microscope slide, four and a half hours on a maize leaf, nine hours
on an artificial diet surface, and more than 28 hours mixed with soil (Maddox, 1977).
Likewise, substrates that provide moisture for microsporidian species that are harmed by
drying promote survival. Nosema algerae does not survive drying. If the water in which N.
algerae spores reside dries completely, N. algerae spores die. Ephemeral pools of water are
not desirable substrates for N. algerae (Maddox b, undated).
2.7.1.8. Food
Host plant/insect interactions probably affect the ability of many species of microsporidia to
infect their hosts. While host/plant interactions with entomopathogenic bacteria and viruses
have been the subject of many studies, the effect of the plant on which the insect host is
feeding on the infection of that insect host by microsporidia has been largely neglected.
Smirnoff (1967) found that certain plants affected the susceptibility of the ugly-nest
caterpillar, Archips cerasivoranus, to microsporidian infections. The mode of action of these
interactions is unknown, and the extent of similar phenomena among the microsporidia
remains unexplored (Smirnoff, 1967).
2.7.1.9. Insect cadavers
It is documented that some species of microsporidia seasonally persist in the environment of
their hosts in infected cadavers (White, 1919; Brooks, 1988; Fuxa, Brooks, 1979), and the
80
cadaver unquestionably provides protection from ultraviolet radiation. It is not clear whether
protection against any other environmental factors incur from overwintering in infected
cadavers (Maddox b, undated).
2.7.1.10. Infected living hosts
Many species of microsporidia persist during unfavorable environmental conditions in
infected, living hosts. Nosema pyrausta may persist throughout the winter as free spores in
maize stalks, but, relative to the development of epizootics in the spring, persistence in living,
diapausing European corn borer larvae is most important (Siegel et al., 1988). This is true for
many species of microsporidia, especially those such as N. pyrausta that are transovarially
transmitted. Microsporidia are present in living, infected hosts (in diapause or aestivation) as
spores or immature development forms (meronts, sporonts, sporoblasts). Different
developmental stages of the host (egg, larva, pupa or adult) may survive through unfavorable
environmental conditions as infected individuals. Eggs of the gypsy moth, Lymantria dispar,
(McManus et al., 1989), pupae of the fall webworm, Hypantria cunea (Nordin, Maddox,
1974), and adults of the alfalfa weevil Hypera postica, (Solter et al., 1993), are examples of
microsporidia that overwinter in infected, living hosts. This becomes much more complicated
when microsporidian species involving alternate hosts are involved (Andreadis, 1993). Many
microsporidia from aquatic insect hosts (especially mosquitoes) require development in an
alternate host as part of the developmental cycle. Microsporidia may overwinter or survive
drought conditions in living, alternate hosts such as copepods in areas where the mosquito
host could not survive. The mosquito may distribute microsporidia from pool to pool
(Dieterich et al., 1994; White et al., 1994). It has been demonstrated that spores of some
species of microsporidia can pass through the digestive tract of predators, both vertebrate and
invertebrate (Kaya, 1977). This serves not only to distribute microsporidia to new locations,
but also to protect microsporidia from unfavorable environmental conditions while they are in
the gut of the predator. Parasitoids often have various associations with the microsporidia of
their hosts (Brooks, 1993). Some associations may involve passive transport, while other
associations may involve active infections in parasitoid larvae and adults. In either case,
microsporidia may be transmitted from infected to healthy hosts. Microsporidia transmitted in
this manner are protected from most unfavorable environmental factors such as ultraviolet
radiation and drying (Maddox b, undated).
2.7.1.11. Insecticides / adjuvants
Because microsporidia are not considered as having potential for development as microbial
insecticides, few studies have been conducted on the direct effects of insecticides on
extracorporeal microsporidian spores. The experiments that have been conducted have shown
that technical preparations of organophospates and pyrethrins have no effect on viability of
spores, but that solvents present in many insecticide formulations often are very harmful to
spores (Maddox, 1977). Most disinfectants, such as sodium hypochlorite, killed spores at very
low concentrations. The spores of Vairimorpha necatrix and Endoreticulatus schubergi have
been formulated with various ajuvants in an effort to protect spores from ultraviolet radiation
(Brooks, 1980). The survival of V. necatrix spores exposed to sunlight greatly increased when
UV protectants, such as Shade, were included in formulations in one study (Kaya, 1977), but
V. necatrix persistence was affected more by spore dosage than by UV protectants in another
(Fuxa, Brooks, 1978).
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2.8. Nosema pyrausta Paillot
2.8.1. Infection and the way of spread of Nosema pyrausta spores
Nosema pyrausta (Microspora, Nosematidae) is a widespread microsporidian pathogen which
produce chronic infections that are frequently panzooic in the O. nubilalis, slows larval
developmental rate, increases larval mortality (Zimmack et al., 1954; Zimmack, Brindley,
1957; Kramer, 1959; Siegel et al.,1986b; Solter et al., 1990), (VanDenburgh, Burbutis, 1962;
Peairs, Lilly, 1974; Indels et al., 1976; Hill, Gary, 1979, cit. Andreadis, 1981), reduces
fecundity and longevity in infected adults (Windels et al., 1976; Bruck et al., 2001) and causes
increase of oxygen consumption throughout the life cycle of infected O. nubilalis larvae
(Lewis et al., 1971). Paillot (1927) first described N. pyrausta from European corn borers
collected in France, and the pathogen was first found by Steinhaus (1951) in the United States
in larval European corn borers from the Midwest. By 1957 the microsporidium was present in
Illinois, and Kramer (1959) noted that it could be an important biological mortality factor of
the corn borer (Siegel et al., 1987). Munderloh et al., (1990) tested spores of two
microsporidia, N. pyrausta (from the European corn borer) and N. furnacalis (from the Asian
corn borer, O. furnacalis) which were harvested from laboratory-reared O. nubilalis
caterpillars and purified by centrifugation through Percoll. Conditions permitting in vitro
germination were defined for both species and found to be different. N. pyrausta spores were
incubated in 0.1 N KOH for 30 min, recovered by centrifugation, and resuspended in 1 ml of
an equal mixture of 1% low melting point (LMP) agarose and L-15B medium at 37 °C to
induce germination. N. furnacalis spores were first washed in 10 mM Na2EDTA in 1 mM
Tris base, pH 7.5, exposed to 0.01 N KOH in 0.17 M KCl for 30 min, centrifuged, and
germinated in 1 ml of an equal mixture of 1% LMP agarose and 0.17 M KCl in 10 mM
Na2EDTA (pH 8), at 37 °C. Eighty to 90% of the spores of each species germinated.
Germinated spores were pipetted into a casting mold. Before electrophoresis, agarose blocks
were incubated 48 hr at 50 degrees C in 10 mM Tris base/100 mM Na2EDTA, pH 7.8, with 1
mg/ml proteinase K and 1% N-laurylsarcosine to release the chromosomal DNA from
sporoplasms. After pulsed-field electrophoresis, ethidium bromide staining revealed 13
chromosomal bands ranging in size from 1390- to 440-kb pairs and 1360- to 440-kb pairs in
N. pyrausta and N. furnacalis, respectively. The difference in size estimates of corresponding
chromosomes in the two species was not more than 60-kb pairs (Munderloh et al., 1990).
During 1991 and 1992 regular parasitism of O. nubilalis larvae by this microsporidium was
observed in Slovakia. Tests discovered the presence of the microsporidian spores only at one
locality in the west part of Slovakia (Dechtice). 16% of the pest larvae were parasitized in
1991, and 30% in 1992. N. pyrausta spores were found maily in Malphigian glands but also in
other parts of the pest digestive tract (Cagáň, 1993). During the tests in 1993 – 1995, the
spores of N. pyrausta were found in 12.5% – 32.5% of the pest larvae at the same locality.
Spores were 4.1 – 4.6 μm long and 2.1μm wide (Bokor, 1998). Detailed study of O. nubilalis
population at the vicinty of Dechtice locality showed, that the infection did not spread from
the center of epidemy (Cagáň et al., 1995; Bokor, 1998). Cagan et al (2006) in later study
investigated in different localities of Slovakia, the Czech Republic and Poland during
September and October of 1991-1995, 1999 and 2003-2005. No N. pyrausta infections of the
larvae was detected in most localities of Slovakia. The percentage of infected larvae achieved
5. 0-44.3 in the localities of Trnava district, namely in the surrounding area of the village of
Dechtice (48 deg 32'N 17 deg 36'E), and 15.0-95.0 in those of Uherské Hradiště district in the
Czech Republic (Uherské Hradiště 49 deg 04'N 17 deg 29'E; Blatnice 48 deg 57'N 17 deg
26'E; Blatnička 48 deg 57'N 17 deg 32'E). The localities with regular infections every year
had a very high infestation of the maize plants by O. nubilalis. Infection caused by N.
82
pyrausta was observed nor in the Labe River valley in the Czech Republic neither in the Odra
River valley in Poland. Size of N. pyrausta spores originated from different localities was not
significantly different (Cagan et al., 2006). N. pyrausta, is one of the most important
biological mortality agents present in corn borer populations. N. pyrausta is well adapted for
its association with the corn borer. Transmission is efficient by both vertical and horizontal
means. Although some disease-induced mortality occurs when larvae are infected by oral
ingestion of spores, the most dramatic mortality occurs when transmission is transovarial
(Windels et al. 1976). Such larvae experience 30-80 % higher mortality than healthy larvae
(Kramer 1959, Windels et al. 1976, Siegel et al. 1987b). Crashes usually occur after several
years of rising corn borer populations and when the prevalence of Nosema nears 100 percent.
Because horizontal transmission of infection in corn borer populations depends on the
probability of healthy larvae inhabiting a corn stalk with infected larvae, the initial infection
level of transovarially (vertical infection) infected larvae and the larval population density are
two of the most important variables affecting infection levels in corn borer populations
(Maddox 1987). The use of horizontal and vertical routes of transmission varies between
species and there is a strong link between transmission and virulence. Horizontal transmission
is characterised by a high parasite burden and associated pathogenicity. In contrast, vertical
transmission is characterised by low virulence, which has led to under-reporting of this
important transmission route. Vertically transmitted microsporidia may also cause male
killing or feminisation of their host, with implications for host population sex ratio and
stability. Phylogenetic analysis shows that vertical transmission occurs in diverse branches of
the Microspora. Dunn and Smith (2001) founnd that there was evidence for vertical
transmission in both vertebrate and invertebrate hosts and conclude that it is a common or
possibly even ubiquitous transmission route within this phylum (Dunn, Smith, 2001).
Infected females lay eggs, which have a high percent infection, on the host plant, usually
maize. Healthy females lay over 30 egg masses, each of which contains from 15 to 18 eggs.
Infected females produce less than half the fertile eggs produced by a healthy female.
(Zimmack, Brindley, 1957; Krammer, 1959). Also Siegel et al., (1986) in his tests confirmed
that corn borer adults infected with N. pyrausta laid 33% fewer egg mases than uninfected
adults and transovarially infected larvae experienced higher mortality than uninfected larvae.
Spore dosage experiments were conducted using first- and third-instar larva, first-instar larvae
had the highest IC50 (concentration of spores at which 50% of the larvae became infected), 26
spores/mm m2 diet surface. N. pyrausta detrimentally affected the development of its host, O.
nubilalis. The larval corn borers tunnel in the stalk of the maize plant, where horizontal
transmission occurs were tested. N. pyrausta infects most body tissues, but the Malpigian
tubules are infected early in the course of the infection causing spores to be passed in the
feces of infected larvae (Zimmack, Brindley, 1957; Krammer, 1959). Sajap and Lewis (1988)
detected, that the infections were also evident in the reproductive tissues in all insects (in fifth
instar larvae) after 7 days exposure of 100, 200, 400 and 800 N. pyrausta spores/mm m2 diet
surface for 48 h, regardless of the stadium in which and the dosages of spores to which the
larvae were exposed. The microsporidian spores were found infecting the epithelial layers and
stroma cells of the larval ovarian tissues. In larvae that had a more intense infection, the germ
cells were also infected. The process of histolysis and histogenesis occurring during the pupal
stage did not interfere with infection of the ovarian tissues. The microsporidian spores
remained in the infected tissues, and infections progressed into adult reproductive tissues,
where trophocytes and oocytes enveloped in follicles were infected. Consequently, these
infections resulted in the transovarial transmission of the microsporidium (Sajap, Lewis,
1988). The production of spores in the excrement of larvae increasing exponentially from
hatch to pupation. The timing of events in the life cycle of the pyralid O. nubilalis can be
important in the transmission and spread of the chronic disease caused by this microsporidium
83
(Solter et. al., 1990). Maize stalks inhabited by infected larvae guickly become contaminated
with N. pyrausta spores and subsequent larval inhabitans of that stalk also become infected.
The frass from corn stalks infested with corn borer larvae falls from larval entrance holes and
broken stalks. Some of this frass falls or is wind blown into leaf sheaths of adjacent plants.
Young larvae often enter the plant at this point, thus coming in contact with the spores. After
hatching, vertically infected larvae may move short distances to adjacent plants providing
another means for the pathogen to sread from plant to plant (Lewis, 1978; Andreadis, 1987).
Since the horizontal spread of infection in corn borer populations depends on the propability
of healthy larvae inhabitating a maize stalk with infected larvae, the initial infection level of
vertically infected larvae and the larval population density are two of the most important
variables affecting infection levels in corn borer populations (Maddox, undated).
Epizootiological studies of the microsporidian N. pyrausta infecting field populations of the
pyralid O. nubilalis in Connecticut demonstrated that while vertical transmission was the
primary way in which N. pyrausta was transferred from one host generation to the next,
horizontal transmission was responsible for the seasonal build-up of infection in each
overlapping generation. During the 1st generation, migration of the larvae O. nubilalis to
adjacent maize stalks was insignificant and increases in the prevalence of N. pyrausta within
the population resulted from horizontal transmission of infection among larvae in the same
stalk. During the 2nd generation, larvae actively dispersed to other maize plants and this
resulted in increased levels of infection. Factors facilitating pathogen dispersal were found to
be high host densities, long periods of larval development, low mortality among young larvae
and, possibly, mechanical transmission by the braconid M. grandii (Andreadis, 1986). In the
transmission of the disease was also interested Solter (1991), who investigated two studies of
transmission of N. pyrausta in adults of the pyralid O. nubilalis. In the first study, O. nubilalis
adults became infected when spores were ingested via a water or food source. In the 2nd
study, uninfected females and their offspring rarely became infected after the females mated
with infected males. Other sources of contamination could be implicated when infection did
occur. Infected males mated as effectively as uninfected males and produced offspring,
although it is suggested that severity of infection could have some effect (Solter, 1991). Solter
et al., (2005) in his later tests investigated vertical and horizontal transmission as means by
which entomopathogenic microsporidia may be isolated in their hosts. O. nubilalis larvae
were challenged with microsporidia isolated from other stalk-boring and row crop
Lepidoptera and were susceptible to seven species. Two species were horizontally
transmitted. A Nosema sp. from Eoreuma loftini was transmitted among O. nubilalis larvae
but not among larvae of the E. loftini host. This species was also vertically transmitted to the
offspring of infected O. nubilalis females. An rDNA sequence showed the E. loftini isolate to
be N. pyrausta, a naturally occurring species in O. nubilalis. Their results suggest that both
horizontal and vertical transmission provide physiological barriers to host switching in the
microsporidia, thus restricting the natural host range (Solter et al., 2005). When the pathogen
persists, it can regulate the borer population far below the carrying capacity of the maize
environment (Onstad, Maddox, 1989). When the typical assumption of a homogeneous or
uniform spatial distribution of hosts was included in the model, disease prevalence tended to
fluctuate in cycles. Mechanistic modelling of spatial dynamics to produce spatial
heterogeneity resulted in convergence to a steady-state level of prevalence. Sensitivity
analysis indicated that spore dissemination and the timing of processes are important. The
validation effort was inconclusive but did show the significance of temperature and latitude
for the population dynamics (Onstad, Maddox, 1989). Nosema sp. had a several detrimental
impact on O. nubilalis larvae and the parasitoids developing within them. Of the 84 % O.
nubilalis dying after exposure to Nosema sp., 35% died as fourth or fifth instars of acute
microsporidiosis. Only 51% of the 52% able to pupate eclosed as infected adults. When
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exposed to 50 spores of Nosema sp./ mm2 Nosema sp. diet surface, O. nubilalis hosts
developed extensive infections in the Malphigian tubules and muscle tissue. All of the
parasitoid larvae that emerged from O. nubilalis infected with Nosema sp. were infected with
this microsporidian. Spores were found in the cells of the midgut epithelium as well as in the
lumen of the alimentary canal. Only 23% of the parasitoids emerging from hosts infected with
Nosema sp. eclosed as adults. All of these eclosed adults were males (Cossentine, Lewis,
1986). Prevalence of N. pyrausta and the population density of the O. nubilalis are
characterized by thre of the four features of population cycle driven by infectious diseases: (1)
peak in percent infection occured shortly after peak in host density, (2) the host population
density fall below the treshold necessary for the maintenance of the epizootic, and (3) when
the population was below this treshold, prevalence declined significantly (Canning, 1982).
Seasonal progress of N. pyrausta in the O. nubilalis was a subject of Siegel et al., (1987) a 4year study of the epizootiology of N. pyrausta in the O. nubilalis. N. pyrausta infections in the
first-generation larvae resulted primarily from transovarial infection. Second-generation N.
pyrausta larval infections resulted from both transovarial infection and horizontal
transmission. There was a significant relationship between larval density and percentage
infection of N. pyrausta for the second generation, whereas no such relationship could be
demonstrated for the first generation. Siegel attempted to determine empirically a critical
density for horizontal transmission in the second generation and concluded that no single
threshold value existed (Siegel et al.,1987).
The timing of events in the life cycle of the O. nubilalis, can be important in the transmission
and spread of the chronic disease caused by this microsporidium. Solter et al., (1989)
performed two experiments with transovarially infected larvae to investigate the dynamics of
the disease. In the first study, mean developmental times of infected and uninfected insects
reared at 30 °C were not significantly different; however, the disease significantly slowed the
development of second- to fifth-instar larvae and pupae reared at 24 °C. In the second study,
the production of spores in the excrement of larvae increased exponentially from hatch to
pupation (Solter, 1989).
Sagers et al., (1996) compared the early events in the in vitro development of two
microsporidia, N. pyrausta and Nosema furnacalis, that infect the European and Asian corn
borers, O. nubilalis and O. furnacalis, respectively. Spores of both species, produced in O.
nubilalis larvae, were activated in alkaline saline solutions and used to infect the Helicoverpa
zea cell line BCIRLHZAM1. In both N. pyrausta and N. furnacalis incubated at 31 oC, the
first sporogonic cycle resulted in the differentiation of early spores that germinated
intracellularly. N. pyrausta showed a 24-hr lag phase followed by a growth phase during
which meronts had an approximate doubling time of 8 hr. Early spore differentiation began at
48 hr pi, and by 72 hr pi infected cells were filled with empty spores. There was a single
increase in the percentage of N. pyrausta infected cells at 72 hr pi as early spore production
creased and the late spores that differentiated subsequently did not germinate intracellularly.
In contrast, N. furnacalis had a 12-hr lag phase followed by a growth period when meronts
had an approximate doubling time of 4 hr. Early spore differentiation was observed 24 hr pi,
and at 34.5 hr pi most infected cells were filled with empty spore cases. Subsequently, N.
furnacalis also differentiated late spores but continued to produce early spores leading to
continued cross-infection of host cells by N. furnacalis during a 7-day culture period. These
results indicate that N. pyrausta and N. furnacalis differ from one another in their patterns of
growthand sporogony in H. zea cell cultures (Sagers et al., 1996). In vitro cell culture systems
are important tools for the experimental and genetic manipulation of obligate intracellular
entomopathogens, such as the microsporidia. Kurtti et al., (2002) introduced N. furnacalis, a
microsporidium of Ostrinia furnacalis, into continuous culture using a Helicoverpa zea cell
line, BCIRLHZAM1 clone G5. Infection of the cell line was initiated by germinating alkali
85
(pH 12)-activated spores in the presence of cells at pH 8. Initial infection levels were low but
the percentage of infected cells increased as parasites spread from infected to uninfected cells.
Infected cultures were first transferred after 1 to 2 weeks. Subsequent transfers were made
every 5 to 6 days by mixing infected (1 part) with uninfected (5 parts) cells. In this manner, a
line of N. furnacalis was maintained for more than 70 transfers with continued formation of
spores. The majority of parasites was undergoing merogony during the first 2 days after
subculturing; sporulating stages predominated after 4 days. Six to 7 days were needed for
maximum spore yield. Efficient cross infection occurred in the subcultures when transfer were
made with cells containing mostly spores, but was retarded when cells harbored mainly
meronts. The spread of infection was apparently due to the formation of spores that
germinated spontaneously in vitro. N. furnacalis maintained in continuous culture for over 70
transfers produced spores that were infective for O. nubilalis. However, after 40 transfers
infectivity and virulence of cultured spores for O. nubilalis declined (Kurtti et al., 2002).
Phoofolo (2001) in his tests used five treatments to exclude naturally occurring predators and
parasitoids, based on body size and flight ability, to assess their effect on O. nubilalis
populations on corn plants. Two initial O. nubilalis egg densities (one egg mass and three egg
masses per plant) were assigned to each treatment. Thirty-five to 84% of O. nubilalis larvae
were infected with N. pyrausta (Phoofolo, 2001). Maintance in natural populations, horizontal
and vertical transmissionof O. Nubilalis larvae was proven by Lewis et all., (2006). The
impact of N. pyrausta on fecundity of adults and survival of larvae has been well documented
in laboratory and field research. In an extensive study covering a 6 year period at one site, we
described the effect of N. pyrausta within O. nubilalis populations in a continuous corn
following corn ecosystem. We documented the presence of the pathogen through all life
stages of O. nubilalis (egg, larva, pupa, adult), by collecting throughout the crop season and
examining each insect stage in the laboratory for the frequency of infection with N. pyrausta.
The percentage of infection with N. pyrausta and magnitude of the O. nubilalis population
fluctuated throughout generation 1 and generation 2. Both horizontal and vertical transmission
played a role in maintaining N. pyrausta in the population in both generations. There were
strong correlations between percentage adults with N. pyrausta and percentage larvae with N.
pyrausta, and between percentage eggs with N. pyrausta and percentage larvae with N.
pyrausta. There was a weak correlation between percentage adults with N. pyrausta and
percentage eggs with N. pyrausta. The percentage of insects infected with N. pyrausta was
always lowest in the egg (Lewis et al., 2006).
2.8.2. Influence Nosema pyrausta spores on the life stages of Ostrinia nubilalis
Windels et al., (1975) made observations on pupal weight, adult longevity, oviposition,
fecundity, and fertility of normal corn borers, which were compared with similar observations
on corn borers infected with N. pyrausta. Of 65 pupae with obvious deformities, 66% were
infected with N. pyrausta. Of 537 moths, 53% of the females and 55% of the males were
infected with N. pyrausta and levels of infection averaged 38.9 and 25.4 million spores/moth,
respectively. Adult longevity, oviposition, fecundity and fertility were adversely affected by
infection with N. pyrausta. Reproduction of infected moths was 39.3% lower than that of
moths with no detectable infection, and heavily infected moths had 52.0% lower reproduction
(Windels et al., 1975). Andreadidis (1984), in his field experiments described the spread of
the disesase in O. nubilalis instars. Disease development in 1st-generation larval populations
was characterized by sharp but progressively slower rates of increase in infection during
larval development. These increases in infection were concurrent with a steady, rapid decline
in population density. Development of N. pyrausta in 2nd-generation larval populations was
cyclic and was characterized by a steady moderate increase in the prevalence of infection
86
during the summer and autumn, and gradual decline throughout the winter. Larval abundance
was also cyclic and tended to have a slower rise and more rapid decline. Annual seasonal
variation in the prevalence of infection and host abundance strongly suggested that, even
when enzootic, N. pyrausta had a direct detrimental effect upon the larval population and
contributed significantly to the natural control of O. nubilalis (Andreadidis, 1984). N.
pyrausta is not extremly virulent but causes some mortality in all life stages of the borer. Its
greatest effect, however, occurs in transovarially infectedlarvae, over 60% of which die before
pupation. Older larvae, infected per os with moderate spore dosages, usually survive to
become infected adults and produce infected offspring. All stages, when infected, are more
susceptible to mortality caused by stress, such as temperature extremes and crowding (Siegel,
1985). Larvae exposed to the microsporidium during the first 2 instars formed abnormal
pupae or emerged as abnormal adults. Infections of later instars reduced average longevity of
resultant adult females by at least 2 days and fecundity by at least 50%. Eggs from infected
adults were contaminated with the microsporidium. The prevalence of transovarial-transovum
infections, determined by the presence of spores in eggs or in emerging larvae, varied with the
spore concentration to which the parent females were exposed and with the time (within the
oviposition period) that the eggs were laid. Per os infection of O. nubilalis larvae with N.
pyrausta is important in maintaining this microsporidium in a population of O. nubilalis as
well as reducing the vitality of the population (Sajap, Lewis, 1992). Bruck et al., (2001) in his
tests compared the influence of microsporidian infection caused by N. pyrausta spores and
temperature on the O. nubilalis egg production and hatch. In studies with O. nubilalis
populations, the mean number of eggs laid per female under optimum conditions (27 ˚C, 65%
relative humidity, 16:8 fotoperiod) was 660, while N. pyrausta-infected females held initially
at 16 ˚C laid 116 eggs per female. In studies with individual mating pairs, N. pyrausta
infection reduced egg production per female 53 and 11% in the 16 and 27 ˚C temperature
regimes, respectively, compared to noninfected females under optimum conditions. Exposure
to 16 ˚C temperatures early in the ovipositional period had a more profound impact on
reducing egg production in N. pyrausta infected than noninfected O. nubilalis (Bruck et al.,
2001). Lewis et al., (2009), also has nfirmed it´s affects on the the basic biology of O.
nubilalis by slowing larval development, reducing percentage pupation, and decreasing adult
longevity, oviposition and fecundity. Infections are maintained in a population by vertical and
horizontal transmission. Success of vertical transmission depends on intensity of infection.
Horizontal transmission is dependent on stage of larval development at time of infection,
quantity of inoculum, and host density. Abiotic and biotic factors coupled with N. pyrausta
usually have an additive effect in decreasing the fitness of O. nubilalis, i.e., cold temperatures
reduce fecundity and increase larval mortality, host plant resistance reduces the number of
larvae per plant. Also, microbial and chemical insecticides are more effective in reducing
plant feeding if the insect is infected with N. pyrausta. Predators in general feed on N.
pyrausta-infected O. nubilalis with no decrease in fitness. Parasitoids do coexist with N.
pyrausta, however, parasitoid fecundity is usually reduced when developing in a N. pyraustainfected host. Previously unreported data are presented on the prevalence of N. pyrausta in O.
nubilalis populations from many parts of the US. These data demonstrate that N. pyrausta
continues to be present and fluctuate in populations of O. nubilalis as it has since its discovery
in the US. Also, the dynamics of its presence remain similar through changes in corn
production including crop rotations, reduced tillage and transgenic insect-resistant varieties
(Lewis et al., 2009).
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2.8.3. Influence of Nosema pyrausta on food consumption
N. pyrausta infection also influence the amount of the food which is received. This relation
was tested by Bruck and Lewis (1999). The effect of Nosema pyrausta infection on food
consumption and utilization by O. nubilalis, was studied under laboratory conditions, using a
semi-synthetic diet. The consumption index, which reflects the rate of food intake in a given
period, differed significantly between the infected and control larvae. Observational studies
were conducted in Iowa in 1995 and 1996 to sample natural enemies of O. nubilalis along
field borders with differing vegetation levels. Maize fields adjacent to three broad classes of
vegetation: herbaceous, intermediate, and wooded, were studied. A maizefield adjacent to
each border class was sampled along the entire length of its respective border. O. nubilalis
larvae collected were evaluated for presence of the entomopathogens Beauveria bassiana and
N. pyrausta and the parasitoid Macrocentrus grandii. There was a negative interaction noted
between larvae parasitized by M. grandii and O. nubilalis larvae infected with N. pyrausta.
This antagonism between the two biotic factors may explain why increased food and shelter
adjacent to maize bordering diverse vegetation did not result in significantly higher parasitism
in limited observations. The levels of entomopathogen infections were also not consistently
influenced by border vegetation type (Bruck, Lewis, 1999). Abdel-Rahman and Cagáň (2001)
in their tests confirmed that infection by N. pyrausta had no significant effect on the total
amount of food consumed by different larval instars of O. nubilalis, but it affected the feeding
period by shortening the development time of the 3rd and 4th instar. The digestibility, weight
gain, growth rate and frass produced did not significantly differ between healthy and N.
pyrausta-infected larvae. In contrast, the efficiency of conversion of ingested food to body
substance was significantly affected by N. pyrausta infection, which resulted in significant
decrease of pupal weight in infected indi viduals. The time of infection was also important;
pupae originating from larvae infected earlier (3rdinstar) were significantly lighter than those
of larvae infected in the 4th or 5th instar (Abdel-Rahman, Cagáň, 2001).
2.8.4. Nosema pyrausta and Bt maize
Transgenic maize, Zea mays L., hybrids expressing crystal protein endotoxin genes from
Bacillus thuringiensis (Berliner) are an increasingly popular tactic for managing the O.
nubilalis in North America. O. nubilalis populations also are often vulnerable to the
ubiquitous entomopathogenic microsporidium N. pyrausta. Reardon et al., (2004) examined
the effect of feeding meridic diet incorporated with purified Cry1Ab on growth, development,
and survival of Nosema-infected and uninfected neonate O. nubilalis. Infected larvae
developed more slowly than uninfected larvae. Increasing the concentration of Cry1Ab in diet
reduced larval development, and this effect was amplified by microsporidiosis. Infected larvae
weighed significantly less than uninfected larvae. The relationship among Nosema infection,
Cry1Ab concentration, and larval weight was fitted to an exponential function. The LC50 of
infected larvae was one-third that of uninfected larvae, indicating that infected larvae are
more vulnerable to toxin (Reardon et al., 2004). Monitoring for resistance to B. thuringiensis
(Bt) toxins in transgenic crops is challenging, in part because alleles conferring resistance
appear to be rare. Consequently, several complementary methods are used to identify, collect
and test putatively resistant individuals. A series of experiments conducted at commercial
seed production facilities explored an alternative sampling method. Larvae of O. nubilalis,
were collected from bins containing Bt hybrid seed corn and their inbred progeny (both F2
and backcross-F2 larvae) were tested for resistance to the Bt toxin Cry1Ab. Marked,
laboratory-reared O. nubilalis larvae also were placed beneath drying corn ears to evaluate
potential contamination of samples by larvae developing on non-Bt corn. Both feral and
88
laboratory-reared larvae were used to examine the causes and levels of mortality of larvae in
drying bins. Screening of larvae on diet containing Cry1Ab failed to provide evidence of
resistance, although insufficient inbred lines survived to make conclusions about the presence
of resistance alleles in larvae originally collected beneath Bt maize. Both larvae from
previously dried non-Bt corn and O. nubilalis moving between adjacent bins are potential
sources of contamination of larvae collected beneath drying Bt corn. Exposure to conditions
inside seed corn drying bins for 3 d significantly increased O. nubilalis mortality. Larvae
collected beneath seed corn also showed infection by the pathogens N. pyrausta and
Beauveria bassiana (Balsamo) Vuillemin, with significant mortality apparently caused by B.
bassiana. While contamination and mortality may limit the application of sampling beneath
drying bins, several modifications could improve the potential utility of the technique
(Prasifka et al., 2006).
2.8.5. Influence of Nosema pyrausta on parasitoids of Ostrinia nubilalis
Cossetine and Lewis (1988) studied the influence of N. pyrausta spores on tachinid parasitoid
L. thompsoni. Pupation of L. thompsoni from hosts infected with N. pyrausta or Nosema sp.
and eclosion of adult parasitoids following development in hosts infected with N. pyrausta
were not significantly reduced. No parasitoids eclosed as adults following development in
hosts infected with Nosema sp. Infection of larvae of O. nubilalis by a nuclear polyhedrosis
virus of the noctuid Rachiplusia ou did not affect pupation or eclosion of L. thompsoni. Viral
inclusion bodies were found within the alimentary canals of larvae of L. thompsoni within
virus-infected hosts (Cossetine, Lewis, 1988).
Trichogramma nubilale females were offered a choice between egg masses of O. nubilalis
infected with the microsporidium N. pyrausta and non-infected egg masses. N. pyraustainfected O. nubilalis eggs were smaller (weight) than non-infected host eggs. T. nubilale
females did not discriminate between infected and N. pyrausta free egg masses. This
microsporidian infection did not significantly affect the sex ratio of emerging wasps.
Significantly fewer and smaller adult parasitoids emerged from infected host eggs than from
non infected eggs (Saleh, Obricki, 1995).
From the aspect of integrated biological control programs there are negative aspects to larval
infection with N. pyrausta. N. pyrausta detrimentally affects M. grandii by reducing preimaginal survival, adult longevity and fecundity (Andreadis, 1980, 1982; Siegel et al., 1986a;
Cossetine, Lewis, 1987; Sajap, Lewis, 1988b). Andreadidis (1980), tested the presence of N.
pyrausta spores in O. nubilalis parasitoid and demostrated, that an introduced braconid
parasite M. grandii, was susceptible to this pathogen as well. Large numbers of N. pyrausta
spores were observed within the midgust of emerging larvae and prepupae of M. grandii.
Infection were not seem in larval parasites developing within infected corn borers prior to
their emergence from the host. Observations of pupae and surviving adults revealed direct
systemic infections of midgut epitheliail, fat body, muscle, nerve, and Maplhigian tubule
cells. There was no sign of infection in gonadal tissue of either host sex. Mature spores from
M. grandii measured and while slightly longer than those observed in the corn borer, did not
differ significantly. No morphological differences between spores of N. pyrausta in M.
grandii and O. nubilalis were discernible at the ultrastructual level (Andreadidis, 1980). Only
39% of M. grandii larvae emerged from N. pyrausta-infected hosts enclosed as adults
(Cossetine, Lewis, 1987). Infection with N. pyrausta also changes the behavior of M. grandii.
Larval wandering, instead of the normal clustering around the host for pupation, occured in
46% of heavily infected cohorts (Orr et al., 1994b). This wandering behavior accounted for
nearly 40% of the mortality in infected parasitoids and was attributed to decreased coccon
89
production by O. nubilalis. This caused parasitoid larave to search for a suitable substrate on
which they spin their coccons. The sex ratio of M. grandii was unaffected by host infectio
level, but the mean number of adults emerging from infected O. nubilalis larvaewas reduced
from an average of 40 in uninfected hosts to an average of 11 in heavily infected hosts (Orr et
al., 1994b). Longevity of adult survivors of both sexes infected with N. pyrausta was
significantly shorter than that recorded for uninfected conrols (Kramer, 1959), (Van
Denburgh, Burbutis, 1962; Peairs, Lilly, 1974; Hill, Gray, 1979; cit Andreadidis 1981; Siegel
et al., 1987). Parasitism levels by M. grandii were also inversely related to prevalence of N.
pyrausta (Andreadis, 1982; Siegel et al., 1986a) and coincident with decline of M. grandii
(Siegel et al.,1986a). Andreadidis (1981) in his work also confirmed the source of infection of
N. pyrausta which is significantly related to corn borer density in the maize field. These
findings strongly suggest that N. pyrausta has a significant adverse affect on field populations
of M. grandii and may help explain the diminishing role of this and other introduced parasites
as natural controls of the corn borer in the United States. Parasites developing within N.
pyrausta-infected borers always acquired systemic infections which inhibited their
development and significantly reduces the longevity of adult survivors. There is a significant
inverse correlation between corn borer infection with N. pyrausta and parasitism by M.
grandii in field populations of O. nubilalis where infections with N. pyrausta are relatively
high. This relatioship not only occured geographically, but from one year to the next and
strongly suggested that N. pyrausta may limit or prevent the establishment of field
populations of M. grandii. Infected M. grandii females are able to transmit N. pyrausta to
their progeny as well as serve as vectors for the pathogen in the laboratory (Siegel et
al.,1985).
Orr et al., (1994b) in his work tested the effects of N. pyrausta on behaviour of the pyralid O.
nubilalis and its parasitoid M. grandii. These were examined in the laboratory. Silk produced
by O. nubilalis larvae around feeding and pupation sites was more frequently diffuse
(cobweblike, unstructured) in diet cups containing N. pyrausta-infected larvae; however,
frequency of diffuse silk production by O. nubilalis larvae was not influenced by M. grandii
parasitism. No evidence was found of N. pyrausta spores in the silk produced by infected O.
nubilalis larvae. Three O. nubilalis cocoon statuses were identified as follows: complete
cocoon, in which thick silk cocoon completely surrounded larvae or larval remains at O.
nubilalis or M. grandii pupation; incomplete cocoon, which was open on one or more sides at
pupation; and no cocoon at pupation. The percentage of O. nubilalis larvae that formed a
complete cocoon or no cocoon was significantly influenced by both infection by N. pyrausta
and parasitism by M. grandii. O. nubilalis larvae that had been either infected or parasitized
displayed 7.2 - and 12.3 - fold increases in activity, resp. Larvae that had been both infected
and parasitized displayed a 45-fold increase in level of activity. Sixty-two to 80% of
parasitoids emerging from hosts with an incomplete cocoon, and >91% emerging from no
cocoon, were unable to spin their own cocoons, wandered from host carcasses, and did not
pupate. The incidence of M. grandii spinning and wandering, and distance wandered, were
independent of N. pyrausta dosage to which host larvae were exposed. Fully fed M. grandii
larvae, which emerged from hosts that had not spun cocoons and were placed in complete
cocoons, were able to pupate successfully and to emerge, regardless of infection status (Orr et
al., 1994a).
2.9. Ostrinia nubilalis and host plants
O. nubilalis colonized maize ( Zea mays L.) after its introduction into Europe about 500 years
ago and is now considered one of the main pests of this crop (Thomas et al., 2003; Bethenod
90
et al., 2005). This pest is known to be polyphagous species. It is known to attack over 200
plants (Lewis, 1975), exept the maize, which is the most frequent host plant of this pest,
(Caffrey, Worthley, 1927).
Maize is the main host plant for O. nubilalis in Slovakia, but the larvae of this pest could be
found on the other plant species – Arthemisia, Polygonum (Cagáň, 1993). In northern
Germany was, O. nubilalis, an important pest of maize, known feeding only on mugwort
(Artemisia vulgaris). In 1983 it was found feeding on maize in the northern part of the Ruhr
district for the first time. Most larvae occurred in the border rows of the fields, and infestation
seemed to be correlated with the degree of infestation of mugwort plants nearby.
Development was faster in the northern than in the southern race (Welling, 1989). In Italy
exept the maize the pyralid O. nubilalis was observed attacking kiwifruit and some cultivars
of peach in the province of Cunea in Piemonte (Ciampolini et al., 1987). Manoljovic (1984a)
studied the survival of larvae of O. nubilalis on 8 cultivated and 8 wild plants in Yugoslavia
in 1974-1977. After infestation with egg masses of the pest, the largest percentage of attacked
plants (88.8%) and greatest larval density (369/100 plants) were observed in the case of hop
in 1976, followed by hemp and maize in 1976 (80.35 and 73.18% damaged plants,
respectively, and 322 and 260 larvae/100 plants). The preferred weeds were common burdock
(Arctium minus) and common mugwort (Artemisia vulgaris), especially in 1975, with 54.66%
and 45.50 damaged plants, respectively, and 80 and 54 larvae/100 plants. In the case of the
other plants (sorghum, tomato, red pepper (Capsicum annuum), millet, mule (Setaria
germanica [S. italica]), nettle (Urtica dioica), thorn apple (Datura stramonium) pigweed
(Amaranthus retroflexus), common reed (Phragmites communis [P. australis]), great burdock
(Arctium lappa) and barnyard grass (Panicum crus-galli [Echinochloa crus-galli])), less than
20% of plants were damaged and the population density of the pest did not exceed 20
larvae/100 plants. Manoljovic (1984a) conducted his tests in laboratory conditions where the
effects of 16 food-plants (8 species of cultivated plants (maize, hops, sorghum, hemp, red
pepper, tomato, millet and mule (Setaria italica (germanica))) and 8 species of weeds) on
larval weight, fecundity and oviposition in O. nubilalis were observed. The heaviest larvae
(94.58-99.35 mg) were obtained from maize plants, followed by hop, sorghum and hemp and
the weeds common burdock (Arctium minus) and common mugwort (Artemisia vulgaris).
Fertility and oviposition were greatest on the plants that yielded the heaviest larvae. The
average fecundity of O. nubilalis on maize exceeded 500 eggs/female in each year of the
study, with a maximum of 594.3 eggs in 1976. The fecundity of females from hops, sorghum
and hemp averaged more than 300 eggs/female, while it exceeded 500 eggs/female on hops in
1976 and sorghum in 1977. Similar fecundity and oviposition capacity were observed on
common burdock and common mugwort (Manoljovic, 1984a). Frolov (1991) carried
experiments out in the Krasnodar region of the Russia in 1987-89 to study survival of larvae
of O. nubilalis, O. nubilalis X O. narynensis and O. scapulalis on leaves of maize, hemp and
burweed [Xanthium strumarium] and population densities on artificial leaf tunnels of maize
and leaves of castor [Ricinus communis], sunflowers and hemp. Significant differences were
observed in the behaviour of 1st-instar larvae of populations adapted to maize and those
adapted to dicotyledonous food-plants, but not in their mortality, when forced to feed on 'own'
and 'alien' food-plants. Differences in photo- and thigmotaxis between 1st-instar larvae of the
2 population groups appeared to be important in determining differing densities during the
final developmental stages when ’own’ and ’alien’ food-plants are populated artificially. In
his later studies, Frolov (1992) investigated larval distribution of the pyralids O. nubilalis and
O. scapulalis in a maize field overgrown with mugwort [Artemisia vulgaris] in the Cherkassy
Region of the Ukraine in 1986-89. In the area of direct contact between the host plants at the
edges of the field, O. scapulalis accounted for 11.9% of the larvae recorded on maize and O.
nubilalis for 8.1% of the larvae recorded on mugwort. Crossing experiments indicated that
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feeding by O. scapulalis larvae on maize at the field edges were not connected with the
effects of hybridization with O. nubilalis. Rather, it was suggested that this situation could be
served as a model of the conditions prevailing when O. nubilalis initially altered its food
preference to cereal crops (Frolov, 1992). O. nubilalis is capable to infest many other plants
including sorghum (Painter, Weibel, 1951; Atkins et al., 1983; Wiseman, 1992; cit. Dyatlova
and Frolov, undated). During 1994-1998 Dyatlova and frolov (undated) compared maize and
sorghum infestations at the scientific crop rotation of the Kuban Experimental Station,
Krasnodar Territory, Russia (two-generation zone of the pest). Overall number of fields
inspected was 11 for sorghum and 21 for maize. Periodical surveys of plants grown at 7-23
constant plots (averaged in size 2.5 m2) per field were done at regular (5-7 days) intervals
during a period of egg-laying to estimate numbers, survival and mortality of eggs. They
summed over all estimates of egg numbers per plot to obtain absolute scores of egg and 1st
instar larval densities per m2 for each field. After a week upon completion of egg-laying
period they sampled late instar larvae by dissecting plants grown at 10-36 randomized plots
sized in average of 1.4 m2. Dyatlova and Frolov observed that the overwintered adults
strongly prefer maize for egg-laying contrary to sorghum. During the first-generation flight
maize was not favored for egg-laying over sorghum. Larval mortality at early instars was
much higher when feeding on sorghum, especially during the second generation. It seems
plausible that sorghum can be used as trap crop to beat borers (Dyatlova, Frolov, undated).
According to Derridj et al., (1999) in fields of Russia sorghum and maize are grown
simultaneously. O. nubilalis oviposition preference changes throughout the growth stages.
There is no preference at the early stages, then the insect prefers maize to sorghum, and when
the maize is flowering and maturing the insect prefers sorghum. Derridj et al., (1999)
demonstrated that on the maize leaf surface are present primary metabolites coming from the
leaf tissues. These substances give physiological and plant specific information. O. nubilalis
females have sensorial sensillae on legs and ovipositor which detect soluble carbohydrates
and malic acid and we observed that host selection for oviposition is linked to these
substances. To explain the insect shift amongst the two plants along with the development,
they analyzed the biochemical composition of the sorghum leaf surfaces in soluble
carbohydrates and malic acid throughout growing stages and compared it to maize.
Sorghum (cultivar: kubanskoe krasnoe 1677) coming from Russia and maize (hybrid: Dea
from Pioneer) were grown in phytotronic chamber and green-houses. Substances were
collected by water spraying at the sunset, derivatized by silylation and quantified by gas
chromatography. Compared to the other plant species already studied, the proportions of
soluble carbohydrates found on sorghum leaf surface are very near from those of maize and
different from the others. Concentrations varied according to leaf position and growth stage.
So the oviposition preference of O. nubilalis between maize and sorghum could be explained
by variations of common metabolites related to plant development. Since sorghum takes more
time to reach the mature stage than maize, this delay in growth stage produces differences in
metabolite concentrations which finally induce host selection shifts for oviposition (Derridj et
al., 1999). To contribute to the understanding of the genus Ostrinia in Japan, larvae of
Ostrinia spp. were collected from known host plants and plants not recorded as hosts. The
morphology and sex pheromones of the collected adults were examined. The host plant ranges
of the 7 Ostrinia spp. in Japan were clarified, and the sex pheromones of the 5 species O.
scapulalis, O. zealis, O. zaguliaevi, O. palustralis and O. latipennis were identified in
addition to that of the Asian corn borer O. furnacalis (Ishikawa et al., 1999).
Dramatic control of O. nubilalis on transgenic maize hybrids has many scientists concerned
about high selection pressure due to toxins expressed by these plants and subsequent O.
nubilalis adaptation. Managing O. nubilalis resistance to transgenic maize is likely to depend
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on a refuge strategy complemented by high expression of Bt protein in the plant. There is a
critical gap of knowledge, however, concerning O. nubilalis refuge. Hellmich et al., (undated)
intend to fill this gap by identifying agronomically useful plants that provide refuge for O.
nubilalis and by quantifying natural refuge within and near maizefields. Candidate crops for
first-generation O. nubilalis refuge (Bay oatsp, roso millet) and second-generation O.
nubilalis refuge (proso millet) have been identified. Refuge values of these crops compared
with non-transgenic maize are high. Preliminary data suggested that non-maize sources of O.
nubilalis are small in Central Iowa. Three weed species, cocklebur, Pennsylvania smartweed
and fall panicum, could be problematic for Bt-maize producers because these species are
complete O. nubilalis hosts. Large larvae will move from these plants to Bt maize. Such
movement, if larvae survive differentially, could threaten the high-dose strategy and could
result in faster selection for corn borers that are resistant to transgenic maize hybrids. The
following plants were evaluated in 1996: German millet, Setaria italica (L.), proso millet,
Panicum milaceum (L.), pearl millet, Pennisetum typhoides (Stapf and Hubb.), Japanese
millet, Echinochloa frumentacea (Link), Siberian millet, Setaria italica (L.), buckwheat,
Fagopyrum esculentum Moench, sunflower, Helianthus annuus (L.), amaranth (several
species evaluated), Amaranthus spp., sorghums, (broom corn, grain and forage varieties)
Sorghum bicolor (L.) Moench, switchgrass, Panicum virgatum (L.), soybeans, Glycine max
(L.), bromegrass, Bromus spp., and oats, Avena sativa (L.). First generation O. nubilalis Results showed that Bay oats (late-maturing forage variety) attract high numbers of first
generation O. nubilalis adults. This was an excellent adult aggregation crop. Adults oviposited
in these plants and O. nubilalis larvae complete development. The refuge value of Bay oats
compared with early-planted commercial varieties of maize ranged from 1.5x to 3.0x (3.0x =
three times more ECB produced compared with non-transgenic corn). Preliminary data
suggest O. nubilalis refuge values differ among oat varieties. German millet and switchgrass
(recently mowed or burned) also were excellent first generation aggregation crops. O.
nubilalis adults oviposited on these plants, but larval mortality was high. No O. nubilalis
survived on the switchgrass. Second generation O. nubilalis - German millet also was an
excellent aggregation plant for second generation adults. Refuge value of proso millet ranged
from 1.0x to 4.0x in both Iowa and North Dakota. Refuge values of the other millets were
lower. Buckwheat, sunflower, amaranth, soybeans, and sorghum produced very few if any O.
nubilalis (Hellmich et al., undated).
O. nubilalis has a very wide host range, attacking practically all robust herbaceous plants with
a stem large enough for the larvae to enter. Vegetables other than maize tend to be infested if
they are abundant before maize is available, or late in the season when senescent maize
becomes unattractive for oviposition; snap and lima beans, pepper, and potato are especially
damaged. Other crops sometimes attacked include buckwheat, grain corn, hop, oat, millet, and
soybean, and such flowers as aster, cosmos, dahlia, gladiolus, hollyhock, and zinnia. Some of
the common weeds infested include barnyardgrass, Echinochoa crus-galli; beggarticks,
Bidens spp.; cocklebur, Xanthium spp.; dock, Rumex spp.; jimsonweed, Datura spp.; panic
grass, Panicum spp.; pigweed, Amaranthus spp.; smartweed, Polygonum spp.; and others. A
one of the first good list of host plants was given by Caffrey and Worthley (1927) (cit.
Capinera, 2000). (Bontemps et al., 2004; Ponsard et al., 2004) determined O. nubilalis as a
polyphagous maize pest species that includes two host races: one feeding on maize (Zea mays
L.) and one feeding on mugwort (Artemisia vulgaris L.) and hop (Humulus lupulus L.). Also
Bethenod et al., (2005) in northern France confirmed two sympatric host races: one feeding
on maize and the other on mugwort and hop. Dres and Mallet (2002) recognized host races as
kinds of species that regularly exchange genes with other species at a rate of more than ca. 1%
per generation, rather than as fundamentally distinct taxa. Host races provide a convenient,
93
although admittedly somewhat arbitrary intermediate stage along the speciation continuum
(Dres, Mallet, 2002). The females feeding on mugwort and maize produced sex pheromones
with different E/Z isomeric ratios of Delta-11-tetradecenyl acetate (Thomas et al., 2003).
Pelozuelo et al., (2004) showed that maize, mugwort, and hop host races of O. nubilalis differ
not only in their host plant but also in the sex pheromone they use. Bethenod et al., (2005)
also showed that mating between the two races may be impeded by differences in the timing
of moth emergence and in the composition of the sex pheromone produced by the females. In
the study, they further investigated the genetic isolation of these two races using strains from
the maize (Z strain) and mugwort (E strain) races selected for diagnostic alleles at two
allozyme loci. In a cage containing maize and mugwort plants and located in natural
conditions, mating between individuals of the same strain occurred more often than mating
between males and females of the E and Z strains. In particular, they obtained no evidence for
crosses between Z females and E males. Bethenod et al., (2005) also found that females of the
Z strain laid their eggs almost exclusively on maize, whereas females of the E strain laid their
eggs preferentially, but not exclusively, on mugwort. These results suggested that the genetic
differentiation between the two host races may also be favored by host-plant preference, one
of the first steps toward sympatric speciation (Bethenod et al., 2005). Target pests may
become resistant to Bacillus thuringiensis (Bt) toxins produced by trangenic maize. Untreated
refuge areas are set aside to conserve high frequencies of susceptibility alleles: a delay in
resistance evolution is expected if susceptible individuals from refuges mate randomly with
resistant individuals from Bt fields. In principle, refuges can be toxin-free maize or any other
plant, provided it hosts sufficiently large pest populations mating randomly with populations
from Bt-maize fields. Leniaud et al., (2006) tried to examine the suitability of several
cultivated or weedy plants [pepper (Capsicum frutescens L.), sorghum (Sorghum spec.),
sunflower (Helianthus annuus L.), cocklebur (Xanthium spec.), cantaloupe (Cucumis melo
L.), and hop (Humulus lupulus L.)] as refuges for O. nubilalis and Sesamia nonagrioides
Lefebvre, two major maize pests in southern Europe. Larvae of both species were collected on
these plants. Their genetic population structure was examined at several allozyme loci. There
was found little or no evidence for an influence of geographic distance, but detected a
significant host-plant effect on the genetic differentiation for both species. O. nubilalis
populations from sunflower, pepper, cocklebur, and sorghum appear to belong to the same
genetic entity as populations collected on maize, but to differ from populations on hop.
Accordingly, females from pepper and cocklebur produced exclusively the 'Z' type sexual
pheromone, which, in France, characterizes populations developing on maize. Qualitatively,
these plants (except hop) could thus serve as refuges for O. nubilalis; however, they may be
of little use quantitatively as they were found much less infested than maize. Sesamia
nonagrioides populations on maize and sorghum reached comparable densities, but a slight
genetic differentiation was detected between both. The degree of assortative mating between
populations feeding on both hosts must therefore be assessed before sorghum can be
considered as a suitable refuge for this species (Leniaud et al., 2006). In Europe, two
sympatric host races are found: one feeds on maize (Zea mays) and the other mainly on
mugwort (Artemisia vulgaris). The two host races are genetically differentiated, seldom
crossing in the laboratory or in the field, and females preferentially lay eggs on their native
host species. We conducted two independent experiments, in field and greenhouse conditions,
to determine whether the two host races are locally adapted to their host species. The effect of
larval density and the performance of hybrids were also investigated. Despite some
differences in overall larval feeding performance, both experiments revealed consistent
patterns of local adaptation for survival and for larval weight in males. In females the same
trend was observed but with weaker statistical support. F1 hybrids did not seem to be
disadvantaged compared with the two parental races. Overall, our results showed that both
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host races are physiologically adapted to their native host. The fitness trade-off between the
two host plants provides a potential driving force for ecological speciation in this species
(Calcagno et al., 2007).
2.9.1. Natural plant resistance
Two corn borer species are the principal maize insect pests in Europe, the European corn
borer, O. nubilalis and the pink stem borer, Sesamia nonagrioides (Lefebvre). Hence, it would
be advisable to evaluate the European maize germplasm for corn borer resistance to generate
European varieties resistant to corn borer attack. The creation of the European Union Maize
Landrace Core Collection (EUMLCC) allowed the screening of most of the variability for
European corn borer resistance present among European maize local populations from France,
Germany, Greece, Italy, Portugal, and Spain, testing a representative sample. The objective of
this study was the evaluation of stem and ear resistance of the EUMLCC to European corn
borer and pink stem borer attack. Populations that performed relatively well under corn borer
infestation for stem and ear damage were 'PRT0010008' and'GRC0010085', among very early
landraces; 'PRT00100120' and 'PRT00100186', among early landraces; 'GRC0010174', among
midseason landraces; and 'ESP0070441', among late landraces. Either the selection that could
have happen under high insect pressure or the singular origin of determined maize populations
would be possible explanations for the higher corn borer resistance of some landraces.
Landraces 'PRT0010008', 'FRA0410090', 'PRT00100186', and 'ESP0090214' would be
selected to constitute a composite population resistant to corn borers and adapted to short
season, whereas populations 'ESP0090033', 'PRT00100530', 'GRC0010174', and
'ITA0370005' would be used to make a resistant composite adapted to longer season (Malvar
et al., 2004). Binder et. al., (2002) tested twelve Peruvian maize, Z. mays; these were
selected because of their relatively high level of field resistance to first-generation O.
nubilalis, larval leaf-feeding. Water extracts of freeze-dried, powdered, leaf tissue were
incorporated into a standard diet, fed to larvae, and the effects on larval growth, development,
and fecundity were measured. Larval and pupal weights were monitored as were the time
elapsed in the larval, pupal, and adult stages. Adult fecundity and egg fertility were
recorded.Two Peruvian accessions significantly reduced female larval and pupal weights,
extended pupal and adult development time, and decreased survival of pupae and adults.
Water extracts also had a pronounced impact on males; two accessions significantly reduced
pupal weight and extended the time required to pupate, and one reduced male survival to
adults. The results indicated that water-soluble factors from resistant Peruvian accessions
inhibit the growth, developmental time, and survival of ECB. These resistance factors could
be useful in the development of maize germplasm with insect-resistant traits (Binder et al.,
2002). Ramputh (2002) tested the strategy of targeting expression of a constitutively regulated
gene to generate H2O2 in the extracellular matrix, to reduce herbivory of O. nubilalis by
transforming maize with germin, a wheat oxalate oxidase (OXO) gene, regulated by the rice
actin promoter elements (pAct-OXO). With two independent transformation events, enzyme
activity was stable over seven generations of backcrossing into three maize inbred lines.
Enzyme activity remained associated with the cell wall debris fraction of water extracted
tissues. Leaf tissue of the germin transgenics had elevated levels of H2O2. In vitro leaf feeding
bioassays demonstrated that O. nubilalis larvae feeding was significantly reduced and larval
growth and development were delayed on all ECB infested germin transgenic lines. This
reduced O. nubilalis feeding was confirmed under field conditions. Most significantly, stalk
tunneling damage, measured at plant harvest, was substantially reduced in all germin
transgenic lines. The reduction of tunneling by 50% in the transgenic lines is indicative of
lower levels of O. nubilalis survival which should be significant in epidemiology. Possible
95
mechanisms of resistance include modifications in plant cell wall chemistry, activation of
pathogen resistance genes and effects of H2O2 and germin on insect physiology (Ramputh,
2002). Ponsard et al., (2004) found that stable carbon isotopes (delta (13) C) are a reliable
indicator of host-plant photosynthetic type (C3 or C4) regardless of adult food and intensity of
metabolism; so even when food or metabolism had a significant effect on wing delta (13) C
values, the magnitude of this effect was too small to obscure the signal characterizing hostplant type. Egg and spermatophore delta (13) C values similarly reflect female and male hostplant type, respectively, regardless of adult feeding. Ponsard et al., (2004) found 224 hostplant species of O. nubilalis in the literature, including 19 species with C4-type
photosynthesis. However, in temperate areas, maize is probably the only significant C4 source
of adult moths. Accordingly, wing delta (13) C values were more variable in field-caught
moths showing a typical C3-type delta (13) C value than in those showing a typical C4-type
delta (13) C value (Ponsard et al., 2004).
2.9.2. Plant base odors influencing Ostrinia nubilalis
O. nubilalis is attracting with special plant odors like Alpha-Terthienyl, a phototoxic
secondary metabolite of various Asteraceae. This shows considerable variation in its
insecticidal activity to different herbivorous lepidopterans. The topical LD 50 (lethal dose for
50% mortality) to the sphingid Manduca sexta was 10 µg/g, to the noctuid Heliothis virescens
474 µ/g/g, and to the pyralid O. nubilalis 698 µg/g. To investigate this differential response,
the toxicokinetics of alpha-[3H]terthienyl prepared by a new exchange process was studied in
3 species. Following either oral or topical administation, larvae of M. sexta were unable to
excrete this allelochemical rapidly. However, H. virescens and O. nubilalis were able to
rapidly clear the chemical from the body via the faeces, preventing lethal concentrations from
reaching the cuticle where light-mediated toxic interactions may occur. After 48 h of feeding
on alpha- [3H]terthienyl-treated diet, the ratio of radiolabel in the body to that in faeces was
58:42 for M. sexta, 32:68 for H. virescens and 16:84 for O. nubilalis. Elimination of 3H after
topical application was much more rapid in O. nubilalis (t1/2 = 8.5 h) compared with H.
virescens (t1/2 = 22 h) or M. sexta (t1/2 = 48 h). Rapid clearance of this phototoxic thiophene
is one method by which tolerant insect herbivores deal with this type of allelochemical in host
plants. (Iyengar et al., 1987). Alpha-Terthienyl and comparative metabolism of alphaterthienyl (2,2':5',2-terthienyl, alpha-T), was investigated in the larvae of 3 species of
economically important Lepidoptera by Iyengar et al. (1990) in his later work. The in vivo
study involved feeding alpha-[3H]T to 5th-instar larvae and monitoring the ratio of alphaT:metabolite in the body and faeces at 24 and 72 h following administration. Analysis of the
body contents (minus gut) of larvae showed slightly (but not significantly) higher levels of the
alpha-T:metabolite ratio in M. sexta than H. virescens or O. nubilalis. However, significantly
increased levels of alpha-T:metabolite in the frass were observed in M. sexta than H.
virescens or O. nubilalis. A significant amount (>40%) of label excreted was parent alpha-T
in all species. Striking differences in the capacity of the midgut microsomes to generate
metabolites was observed in vitro. Alpha-T was metabolised 16 and 30 times faster by
microsomal fractions from H. virescens and O. nubilalis resp., than by those from M. sexta.
Evidence gained by using the synergist piperonyl butoxide suggested that polysubstrate
monooxygenases were major enzymes involved in metabolism. Cytochrome P-450 levels
increased with M. sexta > O. nubilalis > H. virescens: the latter 2 species contained 3 and 4
times more cytochrome P-450, resp., than M. sexta. Diets containing alpha-T at 10 and 30
µg/g had no significant effect on cytochrome P-450 levels in M. sexta or O. nubilalis.
However, for H. virescens, a slight but significant decrease of cytochrome P-450 levels was
observed at these 2 concentrations. The results suggested that increased metabolism, mediated
96
by polysubstrate monooxygenases leading to rapid clearance of this phototoxic thiophene, is
one method by which phytophagous insects deal with this type of allelochemical in host
plants (Iyengar et al.,1990). Udayagiri and Mason (1995) tested oviposition response of the O.
nubilalis to chemical constituents in host plants. They used foliar extracts of maize, pepper
(Capsicum annuum L.) and potato (Solanum tuberosum L.) prepared with use the pentane,
acetone and methanol solvents. In all three host plants, chemicals soluble in pentane
stimulated oviposition. In potato, chemicals extractable in acetone also elicited a positive
oviposition response. When presented with a choice between pentane extracts of maize and
pepper, females preferred maize. No preferences were exhibited between pentane extracts of
corn and potato or pepper and potato. Pentane extracts of corn husks, tassels, silk, and corn
leaves from plants at early whorl and tassel (pre-pollen shed) stages of development also
stimulated oviposition. Similar extracts from plants at 2-leaf and blister (when kernels
resemble blisters) stages were not stimulatory. This indicated that plant phenology affects
chemically mediated oviposition response (Udayagiri, Mason 1995). Udayagiri and Mason
(1999) in later tests tested the chemical basis of oviposition elicitation. In a generalist,
herbivore was determined by examination of oviposition responses in O. nubilalis to maize
chemicals in two-choice laboratory bioassays. A pentane extract of maize leafs stimulated
oviposition and the activity persisted for three days, indicated that, oviposition in O. nubilalis
was elicited by low-volatility chemicals. Chemicals in the extract were fractionated by
column chromatography on Florisil, using a sequence of solvents of increasing polarity.
Bioassays of Florisil fractions indicated that the stimulants were eluted with nonpolar
solvents. Positive bioassay results with an extract prepared by dipping maize leafs in pentane
for 20 sec for extraction of leaf surface chemicals suggested that some of the active material
was present in the leaf epicuticle. Gas chromatographic analyses and comparisons with
retention times of standards suggested the presence of several n-alkanes in the dip extract.
Five n-alkanes - hexacosane, heptacosane, octacosane, nonacosane, and tritriacontane known to be present in the epicuticle of maize leaves were bioassayed, and all five elicited
oviposition responses. These results suggested that oviposition elicitation in O. nubilalis is
influenced by the presence of n-alkanes in the host plant epicuticle Udayagiri, Mason, 1999).
Movement of O. nubilalis was not changed only through the season, but through the day too.
This was observed by Pleasants and Bitzer (1999). Moths of O. nubilalis, were aggregated in
vegetation during the day. Several physical characteristics of vegetation might determine
moth preference. Focused were vegetation types that occur along roadsides adjacent to
maizefields. In the Midwest, roadside vegetation typically consists of brome grass, Bromus
inermis (Leyss). Pleasants and Bitzer (1999), were especially interested in the moth’s
preference for prairie vegetation compared with brome because several states have begun
planting prairie vegetation along roadsides. At 4 central Iowa study sites, the density of moths
was measured in several vegetation types during the 1st and 2nd O. nubilalis generations. For
each vegetation type they also measured its microclimate and its foliage density at 5 vertical
levels. In the 1st generation, moths were most dense in brome, which had 6.9 times more
moths than prairie. In the 2nd generation, moths were most dense in foxtail grass, Setaria spp.
Foxtail had 5.2 times more moths than brome, and brome had 1.6 times more moths than
prairie. In both generations, the moth density in a vegetation type was significantly positively
correlated with foliage density at 60 cm. Microclimate measurements of different vegetation
types were not consistently correlated with moth density. They concluded that O. nubilalis
moths had prefered dense foliage >60 cm tall. They also concluded that replacing roadside
brome and the weedy foxtail with native prairie had the potential to reduce the number of
adult moths breeding near maizefields (Pleasants, Bitzer, 1999).
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2.9.3. Plant odors influencing parasitoids of Ostrinia nubilalis
Not only O. nubilalis, but the natural parasitoids of this pyralid are also influenced with the
plant odors. Manoljovic (1985) carried a study out in Yugoslavia in 1974-1977 on the
behaviour of parasites of O. nubilalis at increased host populations on various food-plants.
When 2 egg clusters of the pest (each containing about 40 eggs) were placed on each
experimental plant immediately before hatching, the number of parasites of the resulting
larvae differed between plant species and years. The largest numbers of parasites of larvae of
O. nubilalis per 100 plants were observed on maize, hemp, hops, common burdock (Arctium
minus) and common mugwort (Artemisia vulgaris). However, the efficiency of the parasites
in reducing the pest population at increased host density was diminished to a considerable
extent on most of the plants. Similar studies (Read et al., 1970; Camors, Payne, 1972; Elzen et
al., 1984; Sugimoto et al., 1988; Turlings et al., 1991; cit. Udayagiri, Jones, 1992) about plant
synomones involved in habitat location behavior of parasitoids were identified. However,the
chemical basis of a parasitoid’s differential response to several food plants of its host has not
been analyzed (Udayagiri, Jones, 1992).
Secondary metabolits of plants play important role in attracting of parasitoids. Two plantderived allelochemicals, berberine and α-terthienyl (α-T), were tested for their effects on the
O. nubilalis, and its endoparasitoid E. terebrans. The compounds were administered to the
host insect in meridic diets, and the responses of the host larvae and parasitoids reared from
treaded hosts were measured in terms of growth parameters and survival. In O. nubilalis,
survival to pupation and adult emergence were reduced significantly by the eclusion of
berberine and α-T in larval diets at a concentration of 100 μg/g. However in the parasitoid,
adverse effect were much more apparent with the α-T treatment than with the berberine
treatment. α-T and one of its metabolites were found in host larvae and in emerged adult
parasitoids and their cocoons. Berberine residues were not detected. The implications of these
responsee to compounds of widely differing physiological properities were discussed with
reference to host plant resistence and biological control. With α-T in the diet, sublethal effects
on O. nubilalis alone were more obvious. Mean time to adult emergence was significantly
prolonged for females fed 31 μg/g α-T. With the 100 μg/g treatment, the duration of the
developmental stages was increased significantly for both males and females. In addition,
pupal and adult weights were significantly reduced with this treatment. These results
confirmed and extended observations first made by Champagne et al., (1986): the growth rate
of O. nubilalis larvae was significantly reduced with 100 μg/g α-T in the diet. In the present
study, survival to pupation and adult emergence of O. nubilalis was also significantly reduced
with 100 μg/g α-T in the diet. Parasitoids reared from host fed diets containing did not exibit
sublethal effects in their gowth, exept for an increase in mean pupal weight in the 31 μg/g
treatment group. Although no significant difference from the controls were apparent in
survival to pupation on any of the berberine treatments, survival to adult emergence was
significantly decreased with 100 μg/g bereberine in the host’s diet. The parasitoids reared
from hosts fed 100 μg/g berebrine did not incur as much mortality (significantly different by
the chi square test at α =0.05) as did the unparasitized host larvae, which suggests that the
parasitoids were less susceptible than their host to the effect of berberine. Parasitoids reared
from hosts fed α-T at concentrations of 10 and 31 μg/g in the diet were similar to the controls
in the growth parameters of surviving insects. However, the male parasitoids reared from
hosts fed 100 μg/g α-T were significantly smaller than the controls. No females were
produced in this treatment group. Mean time to pupation and adult emergence was not
significantly affected by any concentration of α-T. Survival to adult emergence was somewhat
reduced with 31 μg/g treatment (P> 0.90 by the chi square test). However, significant
mortality occurred with 100 μg/g α-T in the host diet. The mortality caused by 100 μg/g α-T
98
was significantly higher (by the chi square test at α = 0.05) in E. terebrans than in the
unparasitized hosts. The parasitoids was apperently more susceptible to the thiophene than its
host (McDougall et al., 1988).
Manoljovic (1984b) studied complex of larval parasites of O. nubilalis on various food-plants
in Yugoslavia in 1974-1977. Parasites were most abundant on the plant species on which the
host population was greatest (maize, hemp, hop, common burdock (Arctium minus) and
common mugwort (Artemisia vulgaris), and parasite populations were greatest in the years of
high host populations. On maize, parasites of O. nubilalis were recorded in all the years of the
study and were highly effective in reducing the pest population. The parasites recorded were
Campoplex alkae, S. viridula, L. thompsoni and E. terebrans; however, in most years, only 2
or 3 of these parasites were recorded. The tachinid L. thompsoni was most frequently recorded
from larvae on maize, sorghum, red pepper (Capsicum annuum), pig weed (Amaranthus
retroflexus), thorn apple (Datura stramonium), common burdock and common mugwort; S.
turionus most frequently attacked larvae on hemp, tomato, thorn apple, common burdock and
common mugwort; E. terebrans was most frequently recorded from larvae on hemp, hop,
common burdock and common mugwort; and S. viridula was the only parasite attacking
larvae on proso millet, mule (Setaria germanica [S. italica]) and barnyard grass (Panicum
crus-galli [Echinochloa crus-galli]).
2.9.4. Weed abundance influencing Ostrinia nubilalis infestation
Weber et al., (1990) tested the influence of weeds on O. nubilalis infestation of maize. Two of
four sweet maize plantings in Massachusetts, each with a broad spectrum of weed abundance
in plots 3 rows by 6 m, showed a positive relationships of ear infestation by O. nubilalis, with
total weed biomass sampled 5 weeks after maize seedling emergence. The relationship was
more apparent with wider row spacing (91 versus 76 cm) and without cultivation. With the
dominant weeds Digitaria sanguinalis, Panicum dichotomiflorum, Amaranthus retroflexus
and Chenopodium album, linear regression showed an increase from about 20% ear
infestation in weedless plots to about 40% infestation in plots with 2000 kg/ha above-ground
dry weight of weeds at week 5 post-emergence. The effect may vary with weed species, and
the data showed a stronger correlation with forb abundance than with grasses. Sweet maize
growers would profit economically by avoiding weedy areas of fields when partial harvests
are undertaken in infested plantings (Weber et al., 1990). Late-instar O. nubilalis movement
could be an important factor for resistant management programs. Hellmich et al., (undated) in
the cage experiments with mixed plantings of transgenic maize and weeds suggest that lateinstar O. nubilalis will move from weeds into transgenic maize. This phenomenon could be
problematic to maize producers and could result in faster selection for corn borers that are
resistant to transgenic maize hybrids. The research also suggested that not all weeds will be
problematic. Hellmich et al., have identified three weed species to date, cocklebur,
Pennsylvania smartweed and fall panicum, that supported the complete development of O.
nubilalis. Other common weeds such as pigweed and water hemp do not have the architecture
to support O. nubilalis neonates. These plants only support tunneling larvae and,
consequently, should not be problematic in transgenic maizefields (Hellmich et al., undated).
Treatment interactions affecting endemic populations of annual grass and broadleaf weeds
(namely, Setaria spp. Panicum dichotomiflorum, Abutilon theophrasti, Chenopodium album,
Polygonum pensylvanicum and Solanum ptycanthum), maize rootworm (Diabrotica spp.)
larvae, maize earworm (H. zea), O. nubilalis, and common rust (Puccinia sorghi) in
sweetcorn were investigated by Wychen et al., (2001) in three field studies near Arlington,
Wisconsin, USA, in 1996 and 1997. The treatments included one cultivation at 42 days after
planting, mix combination of 0.7 kg metolachlor a.i./ha and 0.7 kg cyanazine a.i./ha, and tank
99
mix combination of 2.2 kg metolachlor/ha and 2.2 kg cyanazine/ha. In all environments, weed
biomass was affected only by the weed control treatments with cultivation resulting in the
highest weed biomass. Maize root damage was affected only by the maize rootworm
insecticide treatments in the early- and late-planted environments in 1997 (E97 ad L97). Both
weed control and ear insect (CEW and ECB) control treatments affected maize ear damage by
CEW and ECB. In E97 and L97, more insect ear damage occurred in plots with 1 x herbicide
treatments than in cultivation treatments. In L97, the ear insect treatment decreased ear
damage 55% compared to untreated plots. The interaction between ear insect and weed
control treatments affected the number of maize earworm found per 10 ears in L97. The
interaction between hybrid rust and weed control treatments influenced common rust severity
in all environments. A hybrid rust by maize rootworm by ear insect treatment interaction also
affected common rust severity in E97 and L97. 'Jubilee' hybrid (rust-susceptible) maize
treated with both insecticides had greater common rust severity than nontreated Jubilee maize.
Sweet maize yield was affected most by weed control in all environments, with the lowest
yields occurring in cultivated plots. Sweet maize yield did not differ between the 1 x and 1/3 x
herbicide treatments in all environments. The interaction among hybrid rust by maize
rootwoform by ear insect treatments also affected yield in E97 and L97. An important
component of this interaction was the maize rootworm treatment, as sweet maize yield was
higher in treated than nontreated plots (Wychen et al., 2001).
100
3. GOALS
a) To characterize O. nubilalis population and infestation in Slovakia.
b) To characterize species spectrum of the O. nubilalis parasitoids.
c) To get information about microsporidian infection in north-west part of Slovakia and
south part of Czech Republic.
d) To check the influence of microsporidian infection caused by Nosema pyrausta from
Slovakia on populations of O. nubilalis from various countries.
4. MATERIAL AND METHODS
4.1. Ostrinia nubilalis population and infestation in Slovakia
The natural population of O. nubilalis was studied in Slovakia in autumn, September –
October 2006, 2007, 2008 and 2009. Various locations with maize trials with same maize
hybrids were selected and the number of larvae per maize stalk and the positions of larvae
were observed and noticed. There was winter wheat (Triticum aestivum) or barley (Hordeum
vulgare) as a pre-crop and conventional agrotechnic technique – ploughing at all choosen
locations during the time of all observations. No chemical treatment agains young larvae was
used during the season. Locations were under natural O. nubilalis infestation. Position of
larvae and plant infections (damages) were noticed and caught in simple tables. Locations and
damages caused by O. nubilalis larvae were calculated and marked in simple map.
In autumn 2006, hybrids FAO 280 – 520, DKC 3511, DKC 3320, DKC 3759, DK 391, DKC
4005, DK440, ED 4302, DKC 5143, DKC 4626, DKC 4860, DK 471, DKC 4964, DK 526,
DK 537, DKC 5542, LG 23.06 LG, 33.62, PR38A24, PR37D25, PR37M34, CORALBA
were observed at 5 locations. Hybrids DKC 3511 and DKC 5143 were used as a field control
check. There were DKC 3511, DK 391, DKC 4005, DK 440, DKC 4626, NB 4602, DKC
4442 YG, DK 471, DK 526, DK 5143, DK 537, DKC 5542 observed on the last sixth
location, where one Bt maize hybrid was included, hybrid DK 526 was used as a field control
check. Observated locations: Farárske (Trnava), Šoporňa, Kalná nad Hronom, Veĺký Meder,
Jánošíkovo (Tvrdošovce), Borovce. 100 plants of each entry (6 rows) were observed to
attendance of O. nubilalis larvae.
In autumn 2007, hybrids were divided into two maturity groups FAO 280 – 410 and FAO 410
- 520. There were hybrids DKC 3511, EE 4401, EC 3903, ED 4501, EE 4605, NC 4702,
NC 4703, DKC 4964, DK 440, DK 471, DKC 4626, DKC 4372, DKC 4442 YG, DKC 4860,
PR37M34, PR38A24, PR37D25, NK THERMO in the first FAO group 280 – 410 at seven
locations, hybrid DKC 3511 was used as a field control check and one Bt maize hybrid was
also included at three locations. At six locations hybrids DKC 5143, DKC 4442 YG , EE
4809, ND 4903, ED 5206, NC 5209, DKC 5542, DKC 4626, DKC 4964, DK 471, DK 527,
PR37F73, PR36K67, NK CISKO, NK THERMO in second FAO group 410 – 520 at six
locations. Hybrid DKC 5143 was used as a field control check and one Bt maize hybrid was
also included at one location. Observated locations: Borovce, Soblahov, Perín, Macov, Nacina
Ves, Trhovište, Choňkovce, Parchovany, Čakajovce, Palárikovo, Šoporňa, Veľký Meder. 50
plants of each entry (6 rows) were observed to attendance and position of O. nubilalis larvae.
In autumn 2008, hybrids were divided into three maturity groups FAO 280 – 330, FAO 330 –
410 and FAO 410 – 450. There were hybrids DKC 3511, DK 391, EE 3905, DKC 4005, DK
315, EE 4401, DKC 3759, PR 39D81 and NK Altius in first FAO group 280 – 330 observed
at five locations, hybrid DKC 3511 was used as a field control check. Hybrids DKC 3511,
DKC 3512 YG, DKC 4964, DKC 4490, DKC 4626 DKC 4627 YG, DKC 4372, DKC 4860,
ED5206EZA3, DK 440, DKC 4442 YG, PR37D25 and NK THERMO in second FAO group
101
330 – 410 at five locations, hybrid DKC 3511 was used as a field control check and Bt maize
hybrids have been also included at three locations. At six locations hybrids DKC 5143, EF
4705, NE 4711, DKC 4983, EE 4809, DKC 5170, DKC 4964, DKC 5018 YG, DKC 5276,
DKC 4627 YG, DKC 4626, ED5206EZA2, DK 471, PR37F73, PR36D79, NK CISCO in
third FAO group 410 – 450. Hybrid DKC 5143 was used as a field control check and Bt
maize hybrids were included on one location. Observated locations: Bajč, Sokolce, Veľký
Meder, Tešedíkovo, Macov, Klasov, Borovce, Nitra, Bardoňovo, Kalná nad Hronom,
Čakajovce, Čachtice, Budmerice, Šalgovce. 50 plants of each entry (6 rows) have been
observed to attendance and position of O. nubilalis larvae.
In autumn 2009, hybrids were divided into three maturity groups FAO 280 – 330, FAO 330 –
410 and FAO 410 – 450. There were hybrids DKC3511, PR38A79, DK391, NF3715, DK315,
EE3802 (DKC 4082), PR39D81, NF4217, NKALTIUS checked at five locations, hybrid
DKC 3511 was used as a field control check.
Hybrids DKC3511, PR37D25, EG4405, DKC4490, EF4503, DKC4964, EE4605,
DKC3512YG, DKC3511, NE4610, DK440, DKC 4442YG, NF4726, DKC4626,
DKC4627YG, NKTHERMO, EF4706, DKC5018YG in second FAO group 330 – 410 at six
locations. Hybrid DKC 3511 was used as a field control check and Bt maize hybrids have
been also included at three locations.
At six locations hybrids DKC5143, EF4810, DKC4983, DKC5170, PR37F73, EG4911,
EG5009, PR36D79, DKC4889, EF4705, NE4711, DKC4490, DKC5143, DKC 5018YG,,
DKC4888, DKC4964, NKCISKO, EG4707 in third FAO group 410 – 450. Hybrids DKC
5143 was used as a field control check and Bt maize hybrids were included on two location.
Observated locations: Kalná nad Hronom, Čakajovce, Čachtice, Šalgovce, Borovce, JAcovce,
Šaľa II., Smolinské, Bardoňovo, Palárikovo, Šaľa I., Nitra, Veľký Meder, Matuškovo,
Kameničná. 50 plants of each entry (6 rows) have been observed to attendance and position of
O. nubilalis larvae.
4.2. Occurrence and bionomy of Ostrinia nubilalis parasitoids
Spectrum of the O. nubilalis parasitoids was studied at selected localities in Slovakia and one
locality in Czech Republic. From those, one in west part of Slovakia - Nitra, one in northwestern part of Slovakia – Brezová pod Bradlom. One locality was selected in Czech
Republic - Blatnička. At each locality the maize stalks in late summer and maize stalks after
harvest were checked for presence of larvae of the O. nubilalis and its parasitoids. The larvae
were collected in the summer period –Jul – July - August, and in fall September – October –
November. Collected larvae were loaded in special glass bottles with corrugated paper with
cellophane, squares of agar and wet celulose – the source of food and moisture. The agar was
cooked under constant stirring, until was complete sollution in half of the total amount of
water, depending of the quality of the agar.
Each glass bottle was labeled with the name of location and date of collecting. These glasses
were loaded in the wooden box with perforated walls in outdoor insectary, out of the right sun
shine to keep and save the natural weather conditions. The glasses were controlled every day,
in the later period of fall three times a week. Potentially infected larvae were transferred in
sterile Petri dishes for the next checking of their body changes. Emerged parasitoids were
loaded in alcohol test tubes and determined. Obtained informations about parasitoids were
recorded. The observation continued to the next spring, till the time of pupation of O.
nubilalis. Larvae body changes which suspected the parasitoid presence were transferred in
sterile Petri dishes for the next checking of their body changes. Emerged parasitoids were
counted, noticed and put down in alcohol test tubes and determined.
102
4.3. Microsporidian infection in north-west part of Slovakia and south part of Czech
Republic
Structure of the microsporidian infection was checked at selected localities in north-west parts
of Slovakia and one locality in Czech Republic in the years 2003-2005. Selected localities
were maize fields in north – west part of Slovakia and Czech Republic. At the selected
locality the maize stalks were checked for presence of overwintering larvae of the O.
nubilalis and twenty larvae from each locality were taken. The larvae were collected in the
period September – October – November. Collected larvae were loaded in special glass
bottles with chambers - with strips of corrugated paper. Each bottle was labeled with the
name of the locality and the date whe the larvae were collected. Late in laboratory conditions
the O. nubilalis larvae were killed and their innards were microscopically observed on the
presence of microsporidian spores. Diagnosis of disease was based on the presence of spores
within the Malphigian tubules, the principal site of infection was observed under microscope.
From each sample (20 larvae) were 20 microscope samples prepared – a drop of sterile water
was dropped on the square of glass, the innards of the larva were put into the drop of water,
the fat was taken off and the innards were covered with another square of glass. Each sample
was observed under microscope, where the presence of the N. pyrausta spores was checked.
Obtained records were inserted to the table.
4.4. Influence of microsporidian infection from Slovakia on populations of Ostrinia
nubilalis from various countries
Populations of O. nubilalis from different countries – Romania, Austria, Croatia, Germany,
Slovakia - were collected. Larvae were kept in laboratory conditions, temperature 25±1°C,
relative air humidity 80%, fotoperiod 16:8 in glass bottles with articial food with corrugated
paper with celophane to hide in and pupate. In these choosen populations – there was German
population (1) - 22nd brought up in laboratory conditions, German (2) 23th population
brought in laboratory, Romanian – 11th population brought up in laboratory Austrian 6th
population brought up in laboratory, Slovakian and Serbian populations were natural.
Artificial food was based on the diet, used for laboratory rearing of O. nubilalis larvae.
Water (tap water or distilled water) 1000 ml, agar 20g, saccharose 40g, wheat germ 150g,
lucerne meal 100g, yeast 40g, ascorbic acid 4g, glacial acetic acid 5ml, methyl – p –
hydroxybenzoate (Nipagin) 4g. The diet was prepared as follows:
The agar was cooked under constant stirring, until was complete sollution in half of the total
amount of water, depending of the quality of the agar. The mixure of wheat germ, lucerne
meal, yeast and sugar in the other half of the amount of water was added to the agar solution
and further cooked for 5 –10 minutes under constant stirring. Depending on the quality of the
plants substances and the period of cooking, an eventual replacement of 50-200 ml water
could be also necessary. Towards the end of cooking Nipagin solved in about 20 ml 96%
alcohol was added and mixed. After cooking the mixture below 60°C, glacial acetic and
ascorbic acid (previously mixed with about 50 ml water) were also added and stirred. The still
warm diet was poured directly into vials or jars, where it solidifies in some minute. In glass
jars, it could be stored for weeks in a refrigator (on +5°C). The pH value of the fresh diet was
between 4 to 4.5 (Nagy, 1970).
Emerged adults were loaded into cages with nylon walls, source of food – wet celulose with
honey. Sheets of paper were hanged within the cages to lay the eggs on. Parts of paper with
laid egg masses, were loaded into the glass bottles with artificial food to hatch. New hatched
population of larvae as the adults, were kept in the same laboratory conditions. Glass bottles
were labeled with the name of locality and date of experiment. From each country, 100 larvae
103
were kept under the test, when 50 (+ 5 for infection check) larvae were infected with innards
and spores of N. pyrausta and 50 larvae were the uninfected control. The glass bottle with
artificial food and 55 larvae in (from each country), was infected with innards and spores of
N. pyrausta from Slovak Republic. The innards without body fat from infected larvae with N.
pyrausta were determined under microscope. Microscope samples were prepared – a drop of
sterile water was dropped on the square of glass, the innards of the larva were put into the
drop of water, the fat was taken off and the innards were covered with another square of
glass. Each sample was observed under microscope, where the presence of the N. pyrausta
spores was checked.
Suspension from distilled water and infected innards with spores of N. pyrausta was added on
the surface of an arfiticial food in glass bottle, when the larvae were one or two days old.
Infected glasses were checked everyday and compared with uninfected control in glass
bottles. One week or ten days after infection with spores of N. pyrausta, 5 larvae were
microscopically checked for the presence of spores.
All changes in bionomy and development between infected and uninfected larvae were
recorded. New pupae and adult moths were counted and moths were determined to males and
females. Observations were recorded. New eclosed moths from each glass bottle were loaded
in separated and isolated cages – for infected and uninfected moths in each country, where the
number of egg masses were recorded. All obtained observations and records were inserted to
the table to compare the bionomy between infected and uninfected populations from each
country.
104
RESULTS
5.1. Ostrinia nubilalis population in Slovakia
Ostrinia nubilalis populations in Slovakia have been observed in autumn 2006, 2007, 2008
and 2009. The adult larvae of O. nubilalis pest and the other pests and infections in maize
trials at choosen locations have been checked, counted and the charatcters have been noticed.
Based on the obtained data which are detailed in tables 1. – 48. in- appendix, there were
18800 plants observed in 2006, 10150 in 2007, 10550 in 2008 and 11800 in 2009. Based on
current climatic and agro-ecological conditions the higest damages were observed in 2009 40.26% and 2008 – 32.08%. Both years were climatic favourable and average number of O.
nubilalis larvae per plant reached 0.36 in 2009 and 0.33 in 2008. Years 2006 and especially
2007 whereas strongly influenced by extremely unfavourable conditions which reacted in low
damages, 13.44% in 2006 and 11.99% in 2007. Average number of O. nubilalis larvae per
plant were only 0.15 in 2006 and 0.12 in 2007, what was almost 50% decrease comparing to
years 2008 and 2009. Monitoring of the first year of observations – 2006, was pointed just on
presence of adult larvae in maize stalks and broken maize stalks, what is noticed in tables 1. –
6. – in appendix. Hybrids were not divided into maturity groups as in follow years.
Observations in 2007, 2008 and 2009 were more precise. Observed maize trials were divided
into three maturity goups based on FAO – very early, early and medium what responds to
FAO groups based on maize hybrids maturity 280 – 320, 320 – 390, 390 – 450. Position of
larvae were observed and registered in tables 7. – 48. in appendix, through all years 2007,
2008 and 2009. Based on registered observations O. nubilais is a pest which is well adapted in
conditions of Slovakia and observed each year.
Corelation coefficients between the occurrence of the O. nubilalis or H. armigera larvae and
the occurrence of maize pathogens during 2006 – 2009 are shown in tables R1.1-R1.4. Tables
show, that even there were significant correlations at some locations in some years, there was
not usual to find correlation between the pest and pathogen occurrence.There are some
climatic factors which can influence the density and status of infestations characterized based
on year weather conditions and second generation of pest development which is typical
especially for south part of Slovakia. Influence of climatic conditions through years 2006,
2007, 2008 and 2009 to the the occurrence of damage caused by O. nubilalis larvae are
metioned in tables R2.1. – R2.4. Based on these results there are locations in Slovakia where
are very favourable conditions each year for O.nubilalis damages. There were 4 locations
which were checked min. 3 times in 4 years period – Kalná nad Hronom, Veľký Meder,
Borovce and Čakajovce. Based on obtained results of percentages of damages, the highest
damages caused by O.nubilalis larvae were in years 2008 and 2009, as it has been mentioned
previously. The highest percentage of damage was observed in 2008 at localities Kalná nad
Hronom – 40.67%, Veľký Meder – 39.38% , Čakajovce 28.83% and Borovce 22.29%. This
was the most favourable year. Similar results were registered in 2009 as well, when the
highest percentage of damage was observed in Veľký Meder 40.44%, Borovce 23.40%, Kalná
nad Hronom 18.18% and Čakajovce 16%. As a weakest, due to the O. nubilalis larvae
damages was year 2007. As it has been mentioned before, this year weather conditions were
strongly un-favourable to infestation. At location Veľký Meder was only 15.38% of damages
observed, Borovce 13.08% and Čakajovce only 7.63%. Location Kalná nad Hronom was not
registered in 2007. From the locations, which were not check each year regularly, in 2006 the
lovest percentage of damages was registered in Perín 3.52% and the highest in the same year
in Jánošíkovo (Tvrdošovce) 34%. In 2007 the lowest percentage of damages was observed in
Macov 2.94% and the highest in Soblahov 18.59%, in 2008 the lowest percentage of damages
was observed in Čachtice 8.50% and the highest in Bardoňovo 53.82% and in year 2009 the
105
lowest percentage of infestation was observed in Smolinské 12% and the highest in Čachtice
74.55%. The huge difference of percentage of damage between 2008 and 2009 at location
Čachhtice can be explained by the position of trial. In 2008 the trial was “inserted” inside in
the village, partly surrounded with trees. In 2009 was trial on open area on east-south part of
the hill. All mention locations are situated in West part of Slovakia, except location Perín,
which is situated in east part of Slovakia.
Based on the obtained data the percentage of damages caused by O. nubilalis or H. armigera
for each locality during 2006-2009 has been counted as well, as it is registered in tables
R3.1. – R5.9. There were three locations which have been observed min.3 times in 4 years
period. The highest percentage of damages over 4 years was observed at location Veľký
Meder, where average percentage reached 25.86% and and average percentage of broken
stalks reached 4.16%. Location Kalná nad Hronom reached 24.91% and broken stalks 4.16%,
Borovce 19.28% and broken stalks 5.15%, Čakajovce 17.49% and broken stalks 3.63%. Over
all these data the highest percentage of damage was observed at location Bardoňovo, even this
location was checked only in year 2008 and 2009 which are mentioned as the peaks of O.
nubilalis infestation. As an average of these years Bardoňovo reached 51.58% od O. nubilalis
larvae damages and broken stalks 14.50%.
Over 4 years or regular check in maize trials over 100 various hybrids have been checked to
presence of O. nubilalis larvae, as it is mentioned in tables R4.1 – R4.82. There were only
some hybrids which were planted periodical for 4 years of trialing. Based on these data the
current situation and relation between hybrid and O. nubilalis infestation was checked as well.
Hybrids represent the current market portfolio. Based on registered data, there were no
significant connection between hybrid and O. nubilalis preference. More than the hybrids the
current position of trial and position of location was preferred by O. nubilalis moths and
influenced the infestation.
As all data from O. nubilalis have been collected, results based on average nuber of larvae per
plant have been pointed in the simple map based on the years of observations – figures 1. – 4.,
where yellow color characterizes plant damages caused by O. nubilalis larvae les then 20%,
green - 21 – 40% and red - 41 – 60%. Figure 5. shows observation summary over 4 years
with number of observed plants, % of damage, observed larvae and average number of larvae
per plant. As it has been mentioned before, the paeks of damages caused by O. nubilalis
larvae were strongest in years 2008 and 2009.
Table R1.1. Corelation coefficients between the occurrence of the Ostrinia nubilalis (ON) or
Helicoverpa armigera (HA) larvae and the occurrence of maize pathogens in 2006.
Correlation was calculated from 21 hybrids included to experiment. F – Fusarium, U –
Ustilago, H – Helminthosporium, R - rust
Locality
Farárske
Šoporňa
Kaln. n.Hr.
V. Meder
Jánošíkovo
Perín
Borovce
Average
106
ON-F
-
ON-U
0.024
0.245
0.164
0.170
0.051
0.0235
0.113
ON-H
-
ON-R
-
HA-F
-
HA-U
-
HA-H
-
HA-R
-
Table R1.2. Corelation coefficients between the occurrence of the Ostrinia nubilalis (ON) or
Helicoverpa armigera (HA) larvae and the occurrence of maize pathogens in 2007.
Correlation was calculated from 31 hybrids included to experiment. Coefficients marked by +
show statistically significant relationship between values at the 95,0% or higher confidence
level. . F – Fusarium, U – Ustilago, H – Helminthosporium, R - rust
Locality
Soblahov
Perín
Macov
N. Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
ON-F
-
ON-U
0.112
0.222
0.206
0.090
0.225
0.394+
- 0.203
0.611+
0.549+
0.245
ON-H
-0.248
0.052
-0.371+
0.000
0.119
0.303+
0.020
0.719+
0.000
-0.163
0.203
0.100
0.061
ON-R
-
HA-F
-
HA-U
-0.063
0.028
-0.072
0.530+
0.139
0.021
-0.279
-0.248
0.369+
0.047
HA-H
-
HA-R
-
Table R1.3. Corelation coefficients between the occurrence of the Ostrinia nubilalis (ON) or
Helicoverpa armigera (HA) larvae and the occurrence of maize pathogens in 2008.
Correlation was calculated from 38 hybrids included to experiment. Coefficients marked by +
show statistically significant relationship between values at the 95,0% or higher confidence
level. F – Fusarium, U – Ustilago, H – Helminthosporium, R - rust
Locality
Bajč
V. Meder
Sokolce
Tešedíkovo
Kameničná
Macov
Klasov
Borovce
Nitra
Bardoňovo
Kalna n.Hr.
Čakajovce
Čachtice
Budmerice
Šalgovce
Average
107
ON-F
-
ON-U
0.348+
-0.181
0.498+
0.058
0.185
0.274
-0.087
-0.500+
0.437+
0.114
ON-H
-0.464+
-0.464
ON-R
-
HA-F
-
HA-U
-0.176
-0.104
-0.237
-0.112
-0.076
-0.141
HA-H
0.336+
0.336
HA-R
-
Table R1.4 Corelation coefficients between the occurrence of the Ostrinia nubilalis (ON) or
Helicoverpa armigera (HA) larvae and the occurrence of maize pathogens in 2009.
Correlation was calculated from 45 hybrids included to experiment. Coefficients marked by +
show statistically significant relationship between values at the 95,0% or higher confidence
level. F – Fusarium, U – Ustilago, H – Helminthosporium, R - rust
Locality
Kalna n. Hr.
Čakajovce
Čachtice
Šalgovce
Borovce
Jacovce
Šaľa II.
Smolinské
Bardoňovo
Palárikovo
Šaľa I.
Nitra
V. Meder
Matuškovo
Kameničná
Average
ON-F
-
ON-U
-0.013
-0.335+
0.228
0.007
0.298
0.294
-0.385+
-0.162
-0.268
-0.037
ON-H
-
ON-R
-
HA-F
-
HA-U
0.083
0.266
-0.091
-0.299
-0.129
-0.034
HA-H
-
HA-R
-
Table R2.1. Influence of climatic conditions in 2006 to the occurrence of the damage caused
by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA). Table shows the percentage of
damages at different localities. Damage was observed on 100 plants of 21 hybrids.
Damage caused by ON larvae
Locality
Above
ear
Below
ear
Trnava
Sum
19.04
Šoporňa
16.56
Kalná nad Hr.
15.88
Veľký meder
8.24
Jánošíkovo
Ear
34
Perín
3.52
Borovce
17.28
Average
16.36
108
Broken
stalks
Damage caused
by HA larvae
Ear
Table R2.2. Influence of climatic conditions in 2007 to the occurrence of the damage caused
by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA). Table shows the percentage of
damages at different localities. Damage was observed on 50 plants of 31 hybrids.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
Veľký Meder
Borovce
Average
Damage caused
by HA larvae
Above
ear
1.41
1.89
Below
ear
14.47
2.67
Ear
2.71
3.44
Sum
18.59
8.00
Broken
stalks
9.18
0.00
Ear
1.41
8.22
0.35
1.67
1.33
0.53
0.32
1.00
2.13
1.38
2.63
1.54
1.35
1.41
6.56
5.78
3.05
3.47
3.38
2.63
6.63
7.50
8.31
5.49
1.18
2.11
2.22
10.74
1.47
3.25
3.25
1.63
5.25
3.23
3.37
2.94
10.33
9.33
14.32
5.26
7.63
8.00
9.63
15.38
13.08
10.21
0.59
1.00
2.56
0.00
0.74
0.00
0.00
0.00
0.00
3.38
1.45
4.82
2.67
2.44
22.32
3.79
5.75
1.38
1.38
3.00
1.23
4.87
Table R2.3. Influence of climatic conditions in 2008 to the occurrence of the damage caused
by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA). Table shows the percentage of
damages at different localities. Damage was observed on 50 plants of 38 hybrids.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above
ear
2.00
Below
ear
9.11
Ear
10.00
Sum
21.11
Broken
stalks
2.44
Veľký Meder
6.46
16.77
16.15
39.38
9.54
0.00
Sokolce
3.73
24.00
9.47
37.20
5.60
0.13
Tešedíkovo
2.27
15.87
7.60
25.73
3.60
0.40
Kameničná
2.13
7.73
15.33
25.20
1.07
0.40
Macov
2.27
6.80
7.87
16.93
2.80
0.00
Klasov
1.87
16.93
1.47
20.27
4.53
0.13
Borovce
3.43
13.29
5.57
22.29
6.29
0.14
Nitra
2.27
14.00
2.53
18.80
3.47
0.27
Bardoňovo
12.18
36.55
5.09
53.82
14.73
0.18
Kalná nad Hr.
1.83
36.17
2.67
40.67
6.50
0.00
Čakajovce
4.33
23.50
1.00
28.83
6.33
0.00
Čachtice
0.50
6.50
1.50
8.50
8.50
0.00
Budmerice
0.00
28.33
1.33
29.67
4.83
0.17
Šalgovce
3.33
21.50
1.83
26.67
12.50
0.00
Average
3.24
18.47
5.96
27.67
6.18
0.19
Bajč
109
1.00
Table R2.4. Influence of climatic conditions in 2009 to the occurrence of the damage caused
by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA). Table shows the percentage of
damages at different localities. Damage was observed on 50 plants of 45 hybrids.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Sum
18.18
Broken
stalks
1.82
0.55
2.55
16.00
4.55
0.00
74.36
0.00
74.55
3.09
0.00
2.91
27.45
0.36
30.73
6.91
0.55
Borovce
2.40
17.50
3.50
23.40
5.50
0.00
Jacovce
9.47
28.67
7.47
45.60
4.13
0.53
Šaľa II.
3.67
22.89
5.11
31.67
7.89
0.00
Smolinské
2.24
6.94
2.82
12.00
0.00
0.24
Bardoňovo
6.53
32.00
10.80
49.33
14.27
2.53
Palárikovo
11.47
10.93
20.00
42.40
6.00
1.07
Šaľa I.
5.58
20.95
6.74
33.26
7.47
0.11
Nitra
11.16
14.00
18.32
43.47
7.89
2.42
Veľký Meder
6.67
25.89
7.89
40.44
15.11
0.00
Matuškovo
5.11
24.44
8.56
38.11
4.78
0.44
Kameničná
12.56
12.44
11.11
36.11
13.89
0.44
Average
5.61
22.89
7.18
35.68
6.89
0.59
Above
ear
1.64
Below
ear
14.00
Ear
2.55
Čakajovce
2.55
10.91
Čachtice
0.18
Šalgovce
Kalná nad Hr.
Ear
Table R3.1. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Farárske (Trnava) during 2006-2009. Table shows the percentage of damages.
Damage was observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
19.4
Broken
stalks
-
2007
-
-
-
-
-
-
2008
-
-
-
-
-
-
2009
-
-
-
-
-
-
Average
-
-
-
19.4
-
-
110
-
Table R3.2. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Šoporňa during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Below
ear
-
Ear
-
Sum
16.56
Broken
stalks
-
Damage caused
by HA larvae
Ear
2006
Above
ear
-
2007
1.38
6.63
1.63
9.63
0.00
1.38
2008
-
-
-
-
-
-
2009
-
-
-
-
-
-
Average
-
-
-
-
-
-
-
Table R3.3. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Kalná nad Hronom during 2006-2009. Table shows the percentage of damages.
Damage was observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
15.88
Broken
stalks
-
2007
-
-
-
-
-
-
2008
1.83
36.17
2.67
40.67
6.50
0.00
2009
1.64
14.00
2.55
18.18
1.82
0.55
Average
1.73
25.08
2.61
24.91
4.16
0.27
-
Table R3.4. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Veľký Meder during 2006-2009. Table shows the percentage of damages. Damage
was observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
8.24
Broken
stalks
-
2007
2.63
7.50
5.25
15.38
0.00
3.00
2008
6.46
16.77
16.15
39.38
9.54
0.00
2009
6.67
25.89
7.89
40.44
15.11
0.00
Average
5.25
16.72
9.76
25.86
8.22
1.00
111
-
Table R3.5. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Jánošíkovo (Tvrdošovce) during 2006-2009. Table shows the percentage of damages.
Damage was observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
34
Broken
stalks
-
2007
-
-
-
-
-
-
2008
-
-
-
-
-
-
2009
-
-
-
-
-
-
Average
-
-
-
34
-
-
-
Table R3.6. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Perín during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
3.52
Broken
stalks
-
2007
1.89
2.67
3.44
8.00
0.00
8.22
2008
-
-
-
-
-
-
2009
-
-
-
-
-
-
1.89
2.67
3.44
5.76
0.00
8.22
Average
-
Table R3.7. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Borovce during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
112
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
17.28
Broken
stalks
-
2007
1.67
9.00
3.50
14.17
3.67
1.33
2008
3.43
13.29
5.57
22.29
6.29
0.14
2009
2.40
17.50
3.50
23.40
5.50
0.00
Average
2.50
13.26
4.19
19.28
5.15
0.49
-
Table R3.8. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Soblahov during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
2007
2008
2009
Average
Above ear
1.50
1.50
Below
ear
15.38
15.38
Ear
2.88
2.88
Sum
19.75
19.75
Broken
stalks
9.75
9.75
Damage caused
by HA larvae
Ear
1.50
1.50
Table R3.9. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Macov during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
2007
2008
2009
Average
Above ear
0.35
2.27
1.31
Below
ear
1.41
6.80
4.11
Ear
1.18
7.87
4.52
Sum
2.94
16.93
9.94
Broken
stalks
0.59
2.80
1.69
Damage caused
by HA larvae
Ear
4.82
0.00
2.41
Table R3.10. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Nacina Ves during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
2007
2008
2009
Average
113
Above ear
1.67
1.67
Below
ear
6.56
6.56
Ear
2.11
2.11
Sum
10.33
10.33
Damage caused
by HA larvae
Broken
stalks
1.00
1.00
Ear
2.67
2.67
Table R3.11. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Trhovište during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
2007
2008
2009
Average
Above ear
1.26
1.26
Below
ear
5.47
5.47
Ear
2.11
2.11
Sum
8.84
8.84
Damage caused
by HA larvae
Broken
stalks
2.42
2.42
Ear
2.32
2.32
Table R3.12. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Choňkovce during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
2007
2008
2009
Average
Above ear
0.53
0.53
Below
ear
3.05
3.05
Ear
10.74
10.74
Sum
14.32
14.32
Damage caused
by HA larvae
Broken
stalks
0.00
0.00
Ear
22.32
22.32
Table R3.13. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Parchovany during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
2007
2008
2009
Average
114
Above ear
0.32
0.32
Below
ear
3.47
3.47
Ear
1.47
1.47
Sum
5.26
5.26
Damage caused
by HA larvae
Broken
stalks
0.74
0.74
Ear
3.79
3.79
Table R3.14. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Čakajovce during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
2007
2008
2009
Average
Above ear
1.00
4.33
2.55
2.63
Below
ear
3.38
23.50
10.91
12.59
Ear
3.25
1.00
2.55
2.27
Sum
7.63
28.83
16.00
17.49
Damage caused
by HA larvae
Broken
stalks
0.00
6.33
4.55
3.63
Ear
5.75
0.00
0.00
1.92
Table R3.15. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Palárikovo during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
2007
2008
2009
Average
Above ear
2.13
11.47
6.80
Below
ear
2.63
10.93
6.78
Ear
3.25
20.00
11.63
Sum
8.00
42.40
25.20
Damage caused
by HA larvae
Broken
stalks
0.00
6.00
3.00
Ear
1.38
1.07
1.22
Table R3.16. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Bajč during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
2007
-
-
-
2008
2.00
9.11
10.00
2009
Average
115
Broken
stalks
Damage caused
by HA larvae
Ear
-
-
-
-
-
21.11
2.44
1.00
-
-
-
-
-
-
2.00
9.11
10.00
21.11
2.44
1.00
Table R3.17. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Sokolce during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
2007
-
-
-
2008
3.73
24.00
2009
3.73
Average
Broken
stalks
Damage caused
by HA larvae
Ear
-
-
-
-
-
9.47
37.20
5.60
0.13
-
-
-
-
-
24.00
9.47
37.20
5.60
0.13
Table R3.18. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Tešedíkovo during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
2007
-
-
-
2008
2.27
15.87
2009
-
-
2.27
15.87
Average
Broken
stalks
Damage caused
by HA larvae
Ear
-
-
-
-
-
7.60
25.73
3.60
0.40
-
-
-
-
7.60
25.73
3.60
0.40
Table R3.19. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Kameničná during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Broken
stalks
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
-
-
2007
-
-
-
-
-
-
2008
2.13
7.73
15.33
25.20
1.07
0.40
2009
12.56
12.44
11.11
36.11
13.89
0.44
Average
7.34
10.09
13.22
30.66
7.48
0.42
116
Table R3.20. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Klasov during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
2007
-
-
-
2008
1.87
16.93
2009
1.87
Average
Broken
stalks
Damage caused
by HA larvae
Ear
-
-
-
-
-
1.47
20.27
4.53
0.13
-
-
-
-
-
16.93
1.47
20.27
4.53
0.13
Table R3.21. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Nitra during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
2007
-
-
-
2008
2.27
14.00
2009
11.16
14.00
Average
6.71
14.00
10.42
Broken
stalks
Damage caused
by HA larvae
Ear
-
-
-
-
-
2.53
18.80
3.47
0.27
18.32
43.47
7.89
2.42
31.14
5.68
1.34
Table R3.22. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Bardoňovo during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Broken
stalks
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
-
-
2007
-
-
-
-
-
-
2008
12.18
36.55
5.09
53.82
14.73
0.18
2009
6.53
32.00
10.80
49.33
14.27
2.53
Average
9.36
34.27
7.95
51.58
14.50
1.36
117
Table R3.23. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Čachtice during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Broken
stalks
Damage caused
by HA larvae
Ear
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
-
-
2007
-
-
-
-
-
-
2008
0.50
6.50
1.50
8.50
8.50
0.00
2009
0.18
74.36
0.00
74.55
3.09
0.00
Average
0.34
40.43
0.75
41.52
5.80
0.00
Table R3.24. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Budmerice during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
2007
-
-
-
2008
0.00
28.33
0.00
28.33
Broken
stalks
Damage caused
by HA larvae
Ear
-
-
-
-
-
1.33
29.67
4.83
0.17
1.33
29.67
4.83
0.17
2009
Average
Table R3.25. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Šalgovce during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
Above
ear
-
Below
ear
-
Ear
-
Sum
-
Broken
stalks
-
Damage caused
by HA larvae
Ear
-
2007
-
-
-
-
-
-
2008
3.33
21.50
1.83
26.67
12.50
0.00
2009
2.91
27.45
0.36
30.73
6.91
0.55
Average
3.12
24.48
1.10
28.70
9.70
0.27
118
Table R3.26. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Jacovce during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Damage caused
by HA larvae
Ear
Sum
-
Broken
stalks
-
-
-
-
-
-
-
-
-
-
9.47
28.67
7.47
45.60
4.13
0.53
9.47
28.67
7.47
45.60
4.13
0.53
2006
Above
ear
-
Below
ear
-
Ear
-
2007
-
-
2008
-
2009
Average
-
Table R3.27. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Šaľa II. during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
2006
Above
ear
-
Below
ear
-
Ear
-
2007
-
-
-
Damage caused
by HA larvae
Ear
Sum
-
Broken
stalks
-
-
-
-
-
2008
-
-
-
-
-
-
2009
3.67
22.89
5.11
31.67
7.89
0.00
-
-
-
-
-
-
Average
Table R3.28. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Šaľa I. during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Ear
Sum
-
Broken
stalks
-
-
-
-
-
-
-
-
-
-
5.58
20.95
6.74
33.26
7.47
0.11
5.58
20.95
6.74
33.26
7.47
0.11
2006
Above
ear
-
Below
ear
-
Ear
-
2007
-
-
2008
-
2009
Average
119
Damage caused
by HA larvae
-
Table R3.29. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) at the
locality Smolinské during 2006-2009. Table shows the percentage of damages. Damage was
observed on 50 plants of various hybrids.
Damage caused by ON larvae
Year
Damage caused
by HA larvae
Ear
Sum
-
Broken
stalks
-
-
-
-
-
-
-
-
-
-
2.24
6.94
2.82
12.00
0.00
0.24
2.24
6.94
2.82
12.00
0.00
0.24
2006
Above
ear
-
Below
ear
-
Ear
-
2007
-
-
2008
-
2009
Average
-
Table R4.1. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DKC3511 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Broken
stalks
-
Ear
-
-
-
-
1.5
-
-
52
-
-
15.57
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
-
Kalná n. Hr.
Veľký meder
-
-
-
11.5
18.5
Jánošíkovo
Perín
-
-
-
Borovce
-
-
-
Average
-
-
-
120
Damage caused
by HA larvae
10.5
4.5
10.5
-
Table R4.2. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DK440 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
36
Broken
stalks
-
4
-
-
16
-
-
-
7
-
-
-
-
35
-
-
-
-
-
6
-
-
Borovce
-
-
-
49
-
-
Average
-
-
-
21.86
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
-
Kalná n. Hr.
-
-
-
Veľký meder
-
-
Jánošíkovo
-
Perín
-
Table R4.3. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DKC5143 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
24
Broken
stalks
-
-
21
-
-
-
-
12
-
-
-
-
-
9.5
-
-
Jánošíkovo
-
-
-
9.5
-
-
Perín
-
-
-
3
-
-
Borovce
-
-
-
16
-
-
Average
-
-
-
13.57
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
121
-
Table R4.4. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DKC4626 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
24
Broken
stalks
-
-
5
-
-
-
-
7
-
-
-
-
-
1
-
-
Jánošíkovo
-
-
-
-
-
-
-
43
6
-
Perín
Borovce
49
-
-
Average
-
-
-
19.29
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
-
Table R4.5. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DKC4964 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Broken
stalks
-
Ear
-
-
15
-
-
38
-
-
0
-
-
-
-
-
-
-
16.17
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
-
Kalná n. Hr.
Veľký meder
-
-
-
10
13
Jánošíkovo
-
-
-
Perín
-
-
-
Borovce
-
-
Average
-
-
122
Damage caused
by HA larvae
21
-
Table R4.6. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DKC3320 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
8
Broken
stalks
-
-
10
-
-
-
-
13
-
-
-
-
-
18
-
-
Jánošíkovo
-
-
-
39
-
-
Perín
-
-
-
1
-
-
Borovce
-
-
-
-
-
Average
-
-
-
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
14.83
-
Table R4.7. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DKC3759 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
12
Broken
stalks
-
-
20
-
-
-
-
16
-
-
-
-
-
4
-
-
Jánošíkovo
-
-
-
44
-
-
Perín
-
-
-
9
-
-
Borovce
-
-
-
-
-
Average
-
-
-
17.5
-
-
Below
ear
-
Ear
-
sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
123
-
Table R4.8. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid LG23.06 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
29
Broken
stalks
-
-
21
-
-
-
-
13
-
-
-
-
-
13
-
-
Jánošíkovo
-
-
-
27
-
-
Perín
-
-
-
0
-
-
Borovce
-
-
-
-
-
-
Average
-
-
-
17.17
-
-
Trnava
Above
ear
-
Below
ear
-
Ear
-
Šoporňa
-
-
Kalna n.Hr.
-
Veľký meder
Sum
-
Table R4.9. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DK391 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
14
Broken
stalks
-
-
18
-
-
-
-
26
-
-
-
-
-
17
-
-
Jánošíkovo
-
-
-
38
-
-
Perín
-
-
-
4
-
-
Borovce
-
-
-
41
-
-
Average
-
-
-
22.57
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
124
-
Table R4.10. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4005 during 2006. Table shows the percentage of damages. Damage
was observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
26
Broken
stalks
-
-
7
-
-
-
-
38
-
-
-
-
-
0
-
-
Jánošíkovo
-
-
-
53
-
-
Perín
-
-
-
2
-
-
Borovce
-
-
-
52
-
-
Average
-
-
-
25.43
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
-
Table R4.11. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR38A24 during 2006. Table shows the percentage of damages. Damage
was observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
17
Broken
stalks
-
-
5
-
-
-
-
19
-
-
-
-
-
6
-
-
Jánošíkovo
-
-
-
50
-
-
Perín
-
-
-
10
-
-
Borovce
-
-
-
-
-
-
Average
-
-
-
17.83
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
125
-
Table R4.12. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4860 during 2006. Table shows the percentage of damages. Damage
was observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
16
Broken
stalks
-
-
15
-
-
-
-
21
-
-
-
-
-
13
-
-
Jánošíkovo
-
-
-
33
-
-
Perín
-
-
-
5
-
-
Borovce
-
-
-
-
-
-
Average
-
-
-
17.17
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
-
Table R4.13. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37D25 during 2006. Table shows the percentage of damages. Damage
was observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
20
Broken
stalks
-
-
17
-
-
-
-
29
-
-
-
-
-
6
-
-
Jánošíkovo
-
-
-
58
-
-
Perín
-
-
-
0
-
-
Borovce
-
-
-
-
-
-
Average
-
-
-
21.67
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
126
-
Table R4.14. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK471 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
25
Broken
stalks
-
-
17
-
-
-
-
15
-
-
-
-
-
10
-
-
Jánošíkovo
-
-
-
36
-
-
Perín
-
-
-
3
-
-
Borovce
-
-
-
41
-
-
Average
-
-
-
21.00
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
-
Table R4.15. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37M34 during 2006. Table shows the percentage of damages. Damage
was observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
9
Broken
stalks
-
-
10
-
-
-
-
15
-
-
-
-
-
8
-
-
Jánošíkovo
-
-
-
22
-
-
Perín
-
-
-
3
-
-
Borovce
-
-
-
-
-
-
Average
-
-
-
11.17
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
127
-
Table R4.16 Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on the
maize hybrid DK526 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
11
Broken
stalks
-
-
24
-
-
-
-
9
-
-
-
-
-
6
-
-
Jánošíkovo
-
-
-
20
-
-
Perín
-
-
-
9
-
-
Borovce
-
-
-
9
-
-
Average
-
-
-
12.57
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
-
Table R4.17. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK537 during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
14
Broken
stalks
-
-
18
-
-
-
-
3
-
-
-
-
-
10
-
-
Jánošíkovo
-
-
-
34
-
-
Perín
-
-
-
1
-
-
Borovce
-
-
-
19
-
-
Average
-
-
-
14.14
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
128
-
Table R4.18. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid Coralba during 2006. Table shows the percentage of damages. Damage was
observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
11
Broken
stalks
-
-
35
-
-
-
-
10
-
-
-
-
-
4
-
-
Jánošíkovo
-
-
-
25
-
-
Perín
-
-
-
5
-
-
Borovce
-
-
-
-
-
-
Average
-
-
-
15.00
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
-
Table R4.19. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC5542 during 2006. Table shows the percentage of damages. Damage
was observed on 100 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
15
Broken
stalks
-
-
34
-
-
-
-
12
-
-
-
-
-
9
-
-
Jánošíkovo
-
-
-
28
-
-
Perín
-
-
-
2
-
-
Borovce
-
-
-
21
-
-
Average
-
-
-
17.29
-
-
Below
ear
-
Ear
-
Sum
Trnava
Above
ear
-
Šoporňa
-
-
Kalná n. Hr.
-
Veľký meder
129
-
Table R4.20. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK471 during 2007. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
Above
ear
4
Below
ear
26
Ear
0
0
0
2
2
0
0
0
6
0
2
2
1.50
4
4
10
8
6
0
8
0
6
6
16
7.83
2
0
6
0
14
2
4
4
2
6
2
3.50
Sum
30
6
4
18
10
20
2
12
10
8
14
20
12.83
Broken
stalks
18
0
0
0
4
0
0
0
0
0
0
2
2.00
Damage caused by
HA larvae
Ear
0
4
8
0
4
20
2
6
0
0
2
0
3.83
Table R4.21. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37M43 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Above
ear
4
Below
ear
22
Ear
8
Perín
Macov
0
0
2
0
4
0
Nacina Ves
2
6
0
Trhovište
0
10
2
Choňkovce
0
18
Parchovany
0
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
Soblahov
130
Sum
34
6
Broken
stalks
14
Damage caused by HA
larvae
Ear
2
0
0
0
2
0
8
2
6
12
4
0
18
36
0
28
14
2
2
4
-
-
-
16
-
-
-
0.86
10.29
4.86
16.00
3.14
6.00
Table R4.22. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4964 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V.Meder
Borovce
Average
Above
ear
2
8
0
2
2
0
2
6
Below
ear
10
0
0
4
2
0
2
0
Ear
2
2
0
0
0
10
0
0
2
2
6
Sum
14
10
0
6
4
10
4
6
10
0
0
10
2.83
10
2
10
3.50
0
4
0
2.00
10
6
20
8.33
Broken
stalks
8
0
0
0
2
0
4
0
Damage caused by HA
larvae
Ear
2
8
2
0
2
32
4
6
0
2
0
0
14
2.33
4
2
2
5.50
Table R4.23. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37D25 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
131
Above
ear
0
2
2
0
0
2
0
0.86
Below
ear
8
2
4
4
6
6
6
5.14
Ear
4
0
4
2
2
8
0
2.86
Sum
12
4
10
6
8
16
6
8.86
Broken
stalks
4
0
2
0
0
0
2
1.14
Damage caused by
HA larvae
Ear
0
2
0
2
2
18
6
4.29
Table R4.24. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4626 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
Veľký
Meder
Borovce
Average
Above
ear
0
6
0
Below
ear
14
4
2
Ear
0
4
4
0
0
0
0
0
2
2
6
6
2
0
4
0
8
4
2
12
4
0
4
2
6
10
8
14
4
4
6
12
0
0
0.83
8
16
5.83
4
4
3.67
12
20
10.33
Sum
14
14
Broken
stalks
12
0
2
Damage caused by
HA larvae
Ear
2
32
2
0
2
0
0
0
0
0
4
6
16
4
4
0
0
0
2
1.50
2
0
6.00
Table R4.25. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK440 during 2007. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Above
ear
2
0
0
2
0
4
Below
ear
10
2
0
2
2
4
Ear
0
2
0
0
0
14
Parchovany
Čakajovce
Palárikovo
0
-
2
-
0
-
22
2
-
1.14
3.14
2.29
6.57
Šoporňa
V. Meder
Borovce
Average
132
Sum
12
4
0
4
2
Broken
stalks
2
0
0
2
0
0
Damage caused by
HA larvae
Ear
2
6
4
6
2
20
0
-
2
-
0.57
6.00
Table R4.26. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid NK Thermo during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
Veľký
Meder
Borovce
Average
Damage caused by HA
larvae
Ear
Above
ear
6
2
0
0
6
0
0
0
4
6
Below
ear
16
2
0
4
6
0
4
6
6
10
Ear
10
2
4
0
2
6
2
0
0
2
Sum
32
6
4
4
14
6
6
6
10
18
Broken
stalks
10
0
4
0
8
0
0
0
0
0
0
-
6
-
8
-
14
-
0
-
6
-
2.18
5.45
3.27
10.91
2.00
4.73
0
4
10
4
4
18
2
4
0
0
Table R4.27. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR38A24 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
133
Above
ear
2
6
Below
ear
12
2
Ear
2
2
0
2
0
0
0
1.43
2
12
0
0
4
4.57
0
2
0
16
2
3.43
Sum
16
10
2
16
0
16
6
9.43
Broken
stalks
10
0
0
2
0
0
0
1.71
Damage caused by
HA larvae
Ear
0
12
6
8
4
18
16
9.14
Table R4.28. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4372 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Above
ear
0
4
0
0
Below
ear
16
0
6
4
Ear
8
4
0
0
Trhovište
Choňkovce
Parchovany
Čakajovce
4
0
-
0
4
-
2
8
-
4
6
12
-
Palárikovo
Šoporňa
V.Meder
Borovce
Average
1.33
5.00
3.67
10.00
Sum
24
8
6
Broken
stalks
8
0
0
0
Damage caused by
HA larvae
Ear
2
4
2
2
4
0
-
0
22
-
2.00
5.33
Table R4.29. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4860 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
134
Above
ear
0
0
0
0
2
0
0
-
Below
ear
14
6
0
6
6
0
6
-
Ear
0
0
0
0
2
12
0
-
Sum
14
6
0
6
10
12
6
-
Broken
stalks
6
0
0
0
2
0
0
-
0.29
5.43
2.00
7.71
1.14
Damage caused by
HA larvae
Ear
8
0
6
2
6
18
0
5.71
Table R4.30. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC5542 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
135
Above
ear
4
2
4
0
0
2.00
Below
ear
2
2
2
4
16
5.20
Ear
8
4
4
12
0
5.60
Sum
14
8
10
16
16
12.80
Broken
stalks
0
0
0
0
2
0.40
Damage caused by
HA larvae
Ear
14
4
2
0
0
4.00
Table R4.31. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC3511 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
136
Broken
stalks
8
14
4
0
Damage caused by
HA larvae
Ear
Above
ear
0
4
0
0
Below
ear
20
14
6
0
Ear
4
4
0
4
Sum
24
22
6
4
2
0
0
0
0
0
2
6
2
0
2
0
0
0
0
0
2
10
6
4
6
10
14
2
4
6
0
0
2
2
4
2
14
2
6
20
0
0
0
0
0
0
2
6
2
0
4
0
6
6
8
8
2
6
0
0
6
0
2
36
0
2
2
0
0
-
4
0
2
6
2
-
2
8
0
4
2
-
6
6
0
0
4
12
12
12
22
12
22
22
6
10
4
10
4
-
0
0
2
2
0
-
36
20
8
2
2
-
1.05
5.14
4.29
10.48
2.10
7.71
0
0
2
12
Table R4.32. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR36K67 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused by
HA larvae
Ear
Above
ear
2
0
Below
ear
4
0
Ear
6
2
Sum
12
2
Broken
stalks
0
0
Šoporňa
V. Meder
Borovce
0
0
-
14
18
-
0
4
-
14
22
-
0
0
-
0
2
-
Average
0.50
9.00
3.00
12.50
0.00
3.00
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
10
0
Table R4.33. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid NK Thermo during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
137
Above
ear
6
2
0
0
6
0
0
0
4
6
0
2.18
Below
ear
16
2
0
4
6
0
4
6
6
10
6
5.45
Ear
10
2
4
0
2
6
2
0
0
2
8
3.27
Sum
32
6
4
4
14
6
6
6
10
18
14
10.91
Broken
stalks
10
0
4
0
8
0
0
0
0
0
0
2.00
Damage caused by
HA larvae
Ear
0
4
10
4
4
18
2
4
0
0
6
4.73
Table R4.34. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37F73 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
Above
ear
-
Below
ear
-
Ear
-
Sum
-
Broken
stalks
-
2
2
0
4
2.00
2
4
4
2
3.00
2
4
4
2
3.00
6
10
8
8
8.00
0
0
0
0
0.00
Damage caused by
HA larvae
Ear
4
0
0
4
2.00
Table R4.35. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid NK Cisco during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused by
HA larvae
Ear
Above
ear
0
4
0
0
Below
ear
10
6
4
8
Ear
0
4
0
6
Sum
10
14
4
14
Broken
stalks
0
0
0
0
Borovce
-
-
-
-
-
-
Average
1.00
7.00
2.50
10.50
0.00
2.00
Soblahov
Perín
Macov
Nacina Ves
Trhovište
Choňkovce
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
138
2
2
0
4
Table R4.36. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK527 during 2007. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused by
HA larvae
Ear
Above
ear
Below
ear
Ear
Sum
Broken
stalks
Soblahov
-
-
-
-
-
-
Perín
Macov
-
-
-
-
-
-
-
-
-
-
-
-
Nacina Ves
-
-
-
-
-
-
Trhovište
-
-
-
-
-
-
Choňkovce
-
-
-
-
-
-
0
4
0
-
Čakajovce
4
0
2
Palárikovo
2
0
2
4
0
2
Šoporňa
2
8
2
12
0
6
V. Meder
12
8
6
26
0
6
Borovce
0
8
6
14
0
4
Average
3.20
5.60
3.20
12.00
0.00
4.00
Parchovany
139
Table R4.37. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC5143 during 2007. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused by
HA larvae
Ear
Above
ear
Below
ear
Ear
Sum
Broken
stalks
Soblahov
-
-
-
-
-
-
Perín
Macov
-
-
-
-
-
-
-
-
-
-
-
-
Nacina Ves
-
-
-
-
-
-
Trhovište
-
-
-
-
-
-
Choňkovce
-
-
-
-
-
-
0
0
6
6
0
10
0
4
4
8
0
10
0
6
12
18
0
12
4
4
6
14
0
2
0
0
2
2
0
2
2
2
2
6
0
2
0
10
0
10
0
0
4
4
4
12
0
2
0
0
0
0
0
2
0
22
0
22
0
0
4
10
8
22
0
4
6
2
2
10
0
2
2
0
8
10
8
0
0
6
4
10
0
2
2
10
0
12
6
0
1.60
5.33
3.87
10.80
0.93
3.33
Parchovany
Čakajovce
Palárikovo
Šoporňa
V. Meder
Borovce
Average
140
Table R4.38. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4983 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
18
Broken
stalks
2
40
4
0
10
34
10
2
32
2
34
2
0
2
8
16
26
0
0
Macov
0
8
4
12
0
0
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
3.33
13.33
10.67
27.33
3.00
0.67
Above ear
0
Below ear
6
Ear
12
V. Meder
Sokolce
0
20
20
18
6
Tešedíkovo
0
Kaminičná
Bajč
141
Sum
2
Table R4.39. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC5170 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
30
Broken
stalks
2
26
58
6
0
40
10
52
4
0
4
16
14
34
6
0
Kaminičná
6
8
16
30
0
0
Macov
0
6
2
8
2
0
Klasov
-
-
-
-
-
-
Above ear
0
Below ear
8
Ear
22
Sum
V. Meder
Sokolce
0
32
2
Tešedíkovo
Bajč
Borovce
2
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
2.00
18.33
15.00
35.33
3.33
0.33
142
Table R4.40. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4964 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
0
Below ear
6
Ear
8
Sum
14
Broken
stalks
0
V.Meder
Sokolce
4
6
16
26
6
0
0
28
4
32
4
0
Tešedíkovo
6
10
14
0
Kaminičná
Macov
Klasov
2
0
0
6
8
4
18
2
0
30
26
10
6
4
0
2
0
0
0
2
Borovce
4
4
12
20
12
2
Nitra
2
10
6
18
2
0
Bardoňovo
8
44
2
54
2
0
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
2.60
12.60
8.20
23.40
3.40
0.60
Bajč
143
2
Table R4.41. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC5276 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Above ear
0
Below ear
8
Ear
10
Sum
V.Meder
Sokolce
Tešedíkovo
Kaminičná
8
8
32
0
0
0
34
24
16
2
2
8
48
36
26
Macov
2
2
12
Klasov
-
-
Borovce
-
Nitra
-
Bardoňovo
Bajč
18
Broken
stalks
2
Damage caused
by HA larvae
Ear
0
8
0
24
2
2
0
0
0
0
16
2
0
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
1.67
15.33
11.00
28.00
2.67
0.00
144
Table R4.42. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4626 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Above ear
0
Below ear
14
Ear
12
V. Meder
Sokolce
4
18
24
Tešedíkovo
0
20
8
Kaminičná
4
6
Macov
8
4
Klasov
0
Borovce
6
Nitra
Bajč
Sum
26
-
Broken
stalks
2
Damage caused
by HA larvae
Ear
2
46
4
0
28
6
0
16
26
2
0
6
18
4
0
24
0
24
0
0
18
10
34
6
0
0
30
0
30
0
0
Bardoňovo
0
56
6
62
0
2
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
2.44
21.11
9.11
32.67
2.67
0.44
145
Table R4.43. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37F73 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
6
Below ear
10
Ear
10
Sum
Broken
stalks
26
8
0
V. Meder
Sokolce
4
38
8
50
4
0
0
18
4
22
4
0
Tešedíkovo
4
8
8
20
8
0
Kaminičná
2
0
16
18
2
2
Macov
0
8
14
22
0
0
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
2.67
13.67
10.00
26.33
4.33
0.33
Bajč
146
Table R4.44. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR36D79 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
0
Below ear
12
Ear
4
Sum
16
Broken
stalks
0
V. Meder
Sokolce
12
4
6
22
28
0
6
24
14
44
8
4
Tešedíkovo
6
22
4
32
0
0
Kaminičná
2
8
38
48
2
0
Macov
2
2
6
10
2
0
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
4.67
12.00
12.00
28.67
6.67
1.33
Bajč
147
4
Table R4.45. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid NK Cisco during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
6
Below ear
26
Ear
8
Sum
40
Broken
stalks
4
V. Meder
Sokolce
8
14
16
38
2
0
2
20
24
46
4
0
Tešedíkovo
8
6
8
22
10
6
Kaminičná
0
10
24
34
0
0
Macov
6
0
8
14
8
0
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
5.00
12.67
14.67
32.33
4.67
1.00
Bajč
148
0
Table R4.46. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK471 during 2008. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
6
Below ear
6
Ear
12
Sum
24
Broken
stalks
4
V. Meder
Sokolce
2
38
6
46
2
0
Tešedíkovo
0
0
0
0
0
0
Kaminičná
0
8
12
20
0
0
Macov
2
4
14
20
0
0
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
2.00
11.20
8.80
22.00
1.20
0.00
Bajč
149
0
Table R4.47. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4490 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Bajč
V. Meder
Sokolce
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
0
14
0
-
Klasov
14
0
0
Borovce
6
14
16
36
0
0
Nitra
4
32
4
40
2
0
Bardoňovo
0
62
0
62
12
0
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
2.50
30.50
5.00
38.00
3.50
0.00
Macov
150
Table R4.48. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37D25 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Bajč
V.Meder
Sokolce
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
0
30
0
-
Klasov
30
0
0
Borovce
8
20
4
32
14
0
Nitra
4
24
2
30
0
0
Bardoňovo
26
30
2
58
14
0
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
9.50
26.00
2.00
37.50
7.00
0.00
Macov
151
Table R4.49. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid NK Thermo during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Bajč
V.Meder
Sokolce
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
12
18
6
-
Klasov
36
12
0
Borovce
2
22
0
24
16
0
Nitra
2
14
2
18
8
0
Bardoňovo
0
50
2
52
16
0
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
4.00
26.00
2.50
32.50
13.00
0.00
Macov
152
Table R4.50. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4372 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
0
48
0
-
Klasov
48
6
0
Borovce
10
22
10
42
0
0
Nitra
0
16
0
16
0
0
Bardoňovo
22
22
8
52
20
0
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
8.00
27.00
4.50
39.50
6.50
0.00
Bajč
V. Meder
Sokolce
Macov
153
Table R4.51. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4860 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Bajč
V. Meder
Sokolce
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
0
30
0
-
Klasov
30
2
0
Borovce
0
14
2
16
8
0
Nitra
8
16
4
28
8
0
Bardoňovo
24
32
6
62
22
0
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Macov
Šalgovce
-
-
-
-
-
-
Average
8.00
23.00
3.00
34.00
10.00
0.00
154
Table R4.52. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK440 during 2008. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
4
30
6
-
Klasov
40
12
0
Borovce
4
10
4
18
6
0
Nitra
0
32
2
34
4
0
Bardoňovo
0
36
6
42
4
0
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
2.00
27.00
4.50
33.50
6.50
0.00
Bajč
V. Meder
Sokolce
Macov
155
Table R4.53. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4005 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
Macov
-
-
-
-
-
-
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bajč
V.Meder
Sokolce
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
0
50
2
52
8
0
Čakajovce
2
26
0
28
0
0
Čachtice
0
10
0
10
12
0
Budmerice
0
26
0
26
4
0
Šalgovce
6
4
4
14
24
0
Average
1.60
23.20
1.20
26.00
9.60
0.00
156
Table R4.54. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR39D81 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
Macov
-
-
-
-
-
-
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bajč
V.Meder
Sokolce
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
0
32
0
32
4
0
Čakajovce
14
4
4
22
20
0
Čachtice
2
0
2
4
8
0
Budmerice
0
32
2
34
10
0
Šalgovce
8
20
2
30
12
0
Average
4.80
17.60
2.00
24.40
10.80
0.00
157
Table R4.55. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK315 during 2008. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
Macov
-
-
-
-
-
-
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bajč
V. Meder
Sokolce
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
6
16
2
24
8
0
Čakajovce
2
10
2
14
4
0
Čachtice
0
4
0
4
2
0
Budmerice
0
28
0
28
6
0
Šalgovce
0
30
2
32
6
0
Average
1.60
17.60
1.20
20.40
5.20
0.00
158
Table R4.56. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR38B12 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
Macov
-
-
-
-
-
-
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bajč
V.Meder
Sokolce
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
8
12
8
28
20
0
Čakajovce
0
20
0
20
6
0
Čachtice
0
6
0
6
2
0
Budmerice
0
32
0
32
2
0
Šalgovce
0
14
0
14
14
0
Average
1.60
16.80
1.60
20.00
8.80
0.00
159
Table R4.57. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC5143 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Bajč
Damage caused
by HA larvae
Ear
Above ear
8
Below ear
10
Ear
12
Sum
30
Broken
stalks
2
0
6
18
24
2
2
0
0
10
8
18
2
0
22
0
22
44
20
0
2
16
12
30
8
0
8
26
16
50
6
0
6
18
18
42
6
0
0
20
4
24
0
0
0
34
0
34
4
0
2
28
18
48
4
0
0
12
12
24
4
0
2
8
0
10
0
0
0
2
8
10
0
2
4
8
8
20
2
0
2
10
16
28
2
0
2
2
16
20
4
0
2
16
6
24
2
0
0
10
0
10
2
0
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
-
-
-
-
-
-
Čakajovce
-
-
-
-
-
-
Čachtice
-
-
-
-
-
-
Budmerice
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Average
3.33
13.11
10.78
27.22
3.89
0.22
V.Meder
Sokolce
Tešedíkovo
Kaminičná
Macov
160
Table R4.58. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid NK Altius during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
Macov
-
-
-
-
-
-
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bajč
V. Meder
Sokolce
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
8
28
2
38
8
0
Čakajovce
8
20
0
28
10
0
Čachtice
0
6
2
8
4
0
Budmerice
0
34
0
34
6
0
Šalgovce
6
20
0
26
26
0
Average
4.40
21.60
0.80
26.80
10.80
0.00
161
Table R4.59. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC3759 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
Macov
-
-
-
-
-
-
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bajč
V.Meder
Sokolce
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
0
40
2
42
0
0
Čakajovce
0
30
0
30
0
0
Čachtice
0
0
6
6
24
0
Budmerice
0
24
0
24
6
0
Šalgovce
0
26
0
26
4
0
Average
0.00
24.00
1.60
25.60
6.80
0.00
162
Table R4.60. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK391 during 2008. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Bajč
-
-
-
-
-
-
V. Meder
Sokolce
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
Macov
-
-
-
-
-
-
Klasov
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Kalná n. Hr.
0
56
0
56
16
0
Čakajovce
6
4
4
14
8
0
Čachtice
4
0
4
8
12
0
Budmerice
0
34
2
36
6
0
Šalgovce
0
26
2
28
10
0
Average
2.00
24.00
2.40
28.40
10.40
0.00
163
Table R4.61. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC3511 during 2008. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Tešedíkovo
-
-
-
-
-
-
Kaminičná
-
-
-
-
-
-
2
24
0
26
8
0
10
0
10
20
12
0
0
32
0
32
16
0
2
18
6
26
2
0
6
26
8
40
12
0
0
18
6
24
12
0
0
18
2
20
2
2
8
4
12
24
12
0
6
14
4
24
14
0
24
10
16
50
32
0
20
26
6
52
30
0
10
34
2
46
10
0
0
24
0
24
10
0
0
28
8
36
0
0
0
52
6
58
0
0
8
28
2
38
8
0
2
22
0
24
4
0
0
40
0
40
0
0
0
14
0
14
8
0
0
4
0
4
0
0
0
14
0
14
8
0
0
16
6
22
6
0
0
14
2
16
0
2
0
34
2
36
4
0
6
26
0
32
18
0
0
32
6
38
2
0
8
2
0
10
14
0
4.15
21.26
3.85
29.26
9.04
0.15
Bajč
V. Meder
Sokolce
Macov
Klasov
Borovce
Nitra
Bardoňovo
Kalná n. Hr.
Čakajovce
Čachtice
Budmerice
Šalgovce
Average
164
Table R4.62. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4082 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
2
Below ear
12
Ear
2
Sum
16
Broken
stalks
2
Čakajovce
Čachtice
4
4
0
8
4
0
0
76
0
76
0
0
Šalgovce
0
22
0
22
0
0
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V.Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
Average
1.50
28.50
0.50
30.50
1.50
0.50
Kalna n. Hr.
165
2
Table R4.63. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR39D81 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
0
Below ear
22
Ear
0
Sum
22
Broken
stalks
0
Čakajovce
Čachtice
0
16
0
16
6
0
0
70
0
70
6
0
Šalgovce
8
42
0
0
Borovce
Jacovce
-
-
-
50
-
20
-
-
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V.Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
2.00
37.50
0.00
39.50
8.00
0.00
Kalna n. Hr.
Average
166
0
Table R46.4. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid Altius during 2009. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Above ear
0
Below ear
16
Ear
0
Čakajovce
Čachtice
Šalgovce
6
0
2
16
70
28
0
0
0
Borovce
-
-
Jacovce
-
-
Šaľa II.
-
Smolinské
Bardoňovo
Kalna n. Hr.
Sum
16
22
70
Broken
stalks
0
Damage caused
by HA larvae
Ear
0
30
8
0
8
0
0
0
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V. Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
2.00
32.50
0.00
34.50
4.00
0.00
Average
167
Table R4.65. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK391 during 2009. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
4
Below ear
6
Ear
4
Sum
14
Broken
stalks
4
Čakajovce
Čachtice
2
14
6
22
6
0
0
78
0
78
2
0
Šalgovce
0
6
0
6
2
0
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V. Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
1.50
26.00
2.50
30.00
3.50
0.00
Kalna n. Hr.
Average
168
0
Table R4.66. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR38A79 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
0
Below ear
28
Ear
0
Sum
28
Broken
stalks
0
Čakajovce
Čachtice
2
6
0
8
0
0
0
70
0
70
2
0
Šalgovce
4
14
0
18
4
4
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V. Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
1.50
29.50
0.00
31.00
1.50
1.50
Kalna n. Hr.
Average
169
2
Table R4.67. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK315 during 2009. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Broken
stalks
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Čakajovce
Čachtice
0
0
12
78
4
0
16
78
0
6
0
0
Šalgovce
2
38
2
42
2
0
Borovce
0
28
4
32
2
0
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V.Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
0.50
39.00
2.50
42.00
2.50
0.00
Kalna n. Hr.
Average
170
Table R4.68. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DK440 during 2009. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
4
32
2
-
Borovce
38
6
0
Jacovce
10
22
4
36
2
0
Šaľa II.
10
10
12
32
12
0
Smolinské
8
10
4
22
0
0
Bardoňovo
10
30
16
56
18
0
Palárikovo
8
8
20
36
6
0
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V. Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
8.33
18.67
9.67
36.67
7.33
0.00
Šalgovce
Average
171
Table R4.69. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37D25 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
0
44
2
-
Borovce
46
4
0
Jacovce
12
50
4
66
8
0
Šaľa II.
0
60
0
60
10
0
Smolinské
2
20
0
22
0
0
Bardoňovo
2
34
22
58
14
0
Palárikovo
16
20
22
58
2
0
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V. Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
5.33
38.00
8.33
51.67
6.33
0.00
Šalgovce
Average
172
Table R4.70. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4490 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
4
8
4
-
Borovce
16
4
0
Jacovce
4
40
2
46
0
0
Šaľa II.
2
30
12
44
2
0
Smolinské
8
8
8
24
0
0
Bardoňovo
20
18
12
50
22
0
Palárikovo
12
4
32
48
4
4
Šaľa I.
2
12
6
20
2
0
Nitra
12
12
18
42
6
6
V. Meder
0
26
8
34
14
0
Matuškovo
4
24
8
36
4
0
Kameničná
10
10
6
26
14
0
7.09
17.45
10.55
35.09
6.55
0.91
Šalgovce
Average
173
Table R4.71. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4626 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
6
22
6
-
Borovce
34
10
0
Jacovce
6
28
14
48
4
0
Šaľa II.
0
42
2
44
10
0
Smolinské
4
2
8
14
0
0
Bardoňovo
4
36
2
42
4
4
Palárikovo
4
24
10
38
2
0
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V. Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
4.00
25.67
7.00
36.67
5.00
0.67
Šalgovce
Average
174
Table R4.72. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid NK Thermo during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
16
32
6
-
Borovce
54
32
0
Jacovce
4
30
14
48
6
2
Šaľa II.
0
6
2
8
0
0
Smolinské
0
20
2
22
0
0
Bardoňovo
8
44
14
66
30
0
Palárikovo
8
10
22
40
8
0
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V. Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
6.00
23.67
10.00
39.67
12.67
0.33
Šalgovce
Average
175
Table R4.73. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4964 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
4
16
4
-
Borovce
24
10
0
Jacovce
4
24
6
34
0
4
Šaľa II.
2
46
8
56
6
0
Smolinské
2
4
0
6
0
0
Bardoňovo
10
30
14
54
24
4
Palárikovo
10
6
24
40
8
0
Šaľa I.
2
12
2
16
2
0
Nitra
22
12
20
54
20
0
V.Meder
14
18
8
40
20
0
Matuškovo
0
26
6
32
2
0
Kameničná
8
8
14
30
18
2
7.09
18.36
9.64
35.09
10.00
0.91
Šalgovce
Average
176
Table R4.74. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4983 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
16
20
6
42
18
0
Nitra
10
12
18
40
12
2
V.Meder
4
24
4
32
6
0
Matuškovo
6
14
12
32
6
0
Kameničná
18
10
8
36
24
0
10.80
16.00
9.60
36.40
13.20
0.40
Average
177
Table R4.75. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC5170 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
2
34
2
38
8
0
Nitra
20
20
20
60
12
0
V. Meder
16
18
16
50
26
0
Matuškovo
12
24
4
40
12
0
Kameničná
12
16
10
38
16
0
12.40
22.40
10.40
45.20
14.80
0.00
Average
178
Table R4.76. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR37F73 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
6
22
12
40
4
0
Nitra
10
10
18
38
12
4
V. Meder
4
16
0
20
8
0
Matuškovo
8
30
6
44
12
0
Kameničná
14
8
8
30
14
0
8.40
17.20
8.80
34.40
10.00
0.80
Average
179
Table R4.77. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid PR36D79 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
0
34
2
36
8
0
Nitra
12
20
24
56
16
0
V. Meder
10
26
4
40
28
0
Matuškovo
4
32
2
38
4
0
Kameničná
16
24
14
54
26
0
8.40
27.20
9.20
44.80
16.40
0.00
Average
180
Table R4.78. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4889 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
12
20
8
40
8
2
Nitra
6
8
46
60
0
4
V. Meder
6
22
10
38
8
0
Matuškovo
14
16
16
46
12
0
Kameničná
8
8
8
24
6
0
9.20
14.80
17.60
41.60
6.80
1.20
Average
181
Table R4.79. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC4888 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
8
26
6
40
16
0
Nitra
16
24
24
64
6
2
V. Meder
12
20
8
40
30
0
Matuškovo
10
32
14
56
2
0
Kameničná
14
10
10
34
16
0
12.00
22.40
12.40
46.80
14.00
0.40
Average
182
Table R4.80. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid Cisco during 2009. Table shows the percentage of damages. Damage was
observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
-
-
-
-
-
-
Šaľa I.
8
20
12
40
14
0
Nitra
4
4
10
18
6
6
V. Meder
6
26
6
38
12
0
Matuškovo
8
28
6
42
8
0
Kameničná
24
16
8
48
28
0
10.00
18.80
8.40
37.20
13.60
1.20
Average
183
Table R4.81. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC3511 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Kalna n. Hr.
Čakajovce
Čachtice
Šalgovce
Borovce
Jacovce
Šaľa II.
Damage caused
by HA larvae
Ear
Above ear
4
Below ear
22
Ear
4
Sum
30
Broken
stalks
2
6
16
4
26
8
0
0
14
6
20
2
0
4
8
6
18
6
0
0
14
0
14
2
0
0
8
4
12
2
0
2
78
0
80
4
0
0
70
0
70
2
0
0
70
0
70
0
0
2
30
0
32
6
0
8
22
2
32
12
0
2
38
0
40
6
0
4
24
8
36
4
0
0
14
4
18
2
0
0
22
4
26
10
0
14
12
12
38
6
0
8
46
10
64
8
0
16
22
8
46
4
0
2
4
34
2
40
16
0
10
16
6
32
14
0
0
36
0
36
6
0
2
4
6
12
0
2
4
8
4
16
0
0
0
8
2
10
0
0
6
18
6
30
8
2
8
24
14
46
16
2
8
44
4
56
8
0
18
6
16
40
12
4
14
8
30
52
14
2
6
16
14
36
2
2
Šaľa I.
-
-
-
-
-
-
Nitra
-
-
-
-
-
-
V. Meder
-
-
-
-
-
-
Matuškovo
-
-
-
-
-
-
Kameničná
-
-
-
-
-
-
5.00
25.07
5.87
35.93
6.07
0.53
Smolinské
Bardoňovo
Palárikovo
Average
184
Table R4.82. Damage caused by Ostrinia nubilalis (ON) or Helicoverpa armigera (HA) on
the maize hybrid DKC5143 during 2009. Table shows the percentage of damages. Damage
was observed on 50 plants.
Damage caused by ON larvae
Locality
Damage caused
by HA larvae
Ear
Above ear
Below ear
Ear
Sum
Broken
stalks
Kalna n. Hr.
-
-
-
-
-
-
Čakajovce
Čachtice
-
-
-
-
-
-
-
-
-
-
-
-
Šalgovce
-
-
-
-
-
-
Borovce
-
-
-
-
-
-
Jacovce
-
-
-
-
-
-
Šaľa II.
-
-
-
-
-
-
Smolinské
-
-
-
-
-
-
Bardoňovo
-
-
-
-
-
-
Palárikovo
Šaľa I.
Nitra
V. Meder
Matuškovo
Kameničná
Average
185
-
-
-
-
-
-
12
14
20
46
8
0
8
10
8
26
8
0
0
28
8
36
0
0
10
18
24
52
6
6
12
20
10
42
0
2
12
8
12
32
10
0
12
38
8
58
20
0
20
16
8
44
24
0
0
42
18
60
6
0
8
26
12
46
8
0
0
30
6
36
2
0
0
34
10
44
0
0
6
8
8
22
4
2
10
8
10
28
8
2
16
20
10
46
16
0
8.40
21.33
11.47
41.20
8.00
0.80
Figure 1. Occurence of O. nubilalis in Slovakia during 2006. Yellow - les then 20% damaged
plants, green - 21 – 40% damaged plants, red - 41 – 60% damaged plants.
Figure 2. Occurence of O. nubilalis in Slovakia during 2007. Yellow - les then 20% damaged
plants, green - 21 – 40% damaged plants, red - 41 –60% damaged plants.
186
Figure 3. Occurence of O. nubilalis in Slovakia during 2008. Yellow - les then 20% damaged
plants, green - 21 – 40% damaged plants, red - 41 –60% damaged plants.
Figure 4. Occurence of O. nubilalis in Slovakia during 2009. Yellow - les then 20% damaged
plants, green - 21 – 40% damaged plants, red - 41 –60% damaged plants
187
Figure 5. Ostrinia nubilalis observation summary over 4 years with number of observed
plants, % of damage, observed larvae and average number of larvae per plant.
5.2. Occurrence and bionomy of Ostrinia nubilalis parasitoids
Occurrence of Ostrinia nubilalis parasitoids at selected localities of Slovakia and Czech
Republic is marked in tables 5.1. – 5.8. After observations which were evaluated in the years
2003 and 2004, when the parasitation of O. nubilalis was observed, the most abundant
parasitoids in the each locality were - Sympiesis viridula (Thomson), Lydella thompsoni
(Herting), Microgaster tibialis (Nees), Sinophorus turionus (Ratz). All registerd data are
shown in follow parts named by current parasitoid. tables 5.1. – 5.8 shows the results obtained
from the observations conducted in 2003 – 2004. There was 7350 larvae of O. nubilalis
collected in 2003, from which 97 pupae of S. viridula were found and the parazititation
reached 1.32%, 114 pupae of L. thompsoni - 1.55% parazititation, 7 pupae of M. tibialis –
0.09% parazititation and 17 pupae of S. turionus 0.23% of parazititation. In year 2004, from
the 7358 collected larvae of O. nubilalis only 8 pupae of S. viridula were found, and the
parazititation reached 0.16%, 14 pupae of L. thompsoni –0.19% parazititation, 24 pupae of M.
tibialis –0.32% parazititation and 5 pupae of S. turionus –0.06% parazititation. The
differences were evident in each of observed parasitoid, in two years collection. Parazititation
caused by S. viridula in the year 2003 reached 1.32% when 97 pupae of parasitoid were found
and there were only 8 pupae found next year. There was 50 pupae of S. Viridula found at
Blatnička locality in 2003 and this locality was the only one, where pupae of this parasitoid
were found in 2004 as well. Similar results were observed in the case of L. thompsoni, but
here the result could be influenced by the fact, that in year 2003 were counted pupae collected
in the period 25.8. 2003 to 1.12. 2003, plus pupae emerged in the next spring 2004. In this
period the whole number reached number 114 pupae. In the result from the year 2004, were
counted only the pupae collected in the period 23.7. 2004 - 5.11. 2004. In 2003 at Veľký Krtíš
locality, 41 pupae were collected, in Nitra locality 53 pupae were collected. There were only
10 pupae in Nitra collected next year. The decrease was also observed in locality Blatnička,
where in year 2004 only 3 pupae were collected and in locality Brezová pod Bradlom only 1
188
pupa was collected. Increase of collected pupae was observed in the case of M. tibialis, where
in two localities, the pupae were found in both years – Brezová pod Bradlom and Blatnička –
the number of collected pupae increased. In year 2003 at Brezová pod Bradlom locality 4
pupae were found, in year 2004, 17 pupae were found; in locality Blatnička in year 2003, 3
pupae were foud and in year 2004, 7 pupae were found. At Nitra locality any pupa was not
found in both years and at Veľký Krtíš locality was not found any pupa in 2003 too. In case of
M. tibialis the whole parazititation increased from 0.09% to 0.32 % and in both localities the
parazititation increased too. S. turionus parazitation in one locality Brezová pod Bradlom
increased from 0.16% to 0.26%, when in year 2003 on this locality only 1 pupa was found
and in the year 2004, 4 pupae were found. At Blatnička locality was observed decrease of
collected pupae, when in year 2003, 9 pupae were found and in 2004 only 1 pupa was found
and the parazitation decreased from 0.18% to 0.02%, from collected larvae. At Nitra locality
in year 2003, 4 pupae were collected and in locality Veľký Krtíš 3 pupae were collected. In
the next year 2004 any pupa was not found in locality Nitra and locality Veľký Krtíš was
absent.
5.2.1. Sympiesis viridula
Table R5.1. Parasitization of Ostrinia nubilalis (ON) larvae caused by Sympiesis viridula
(SV) at four localities of Slovak and Czech Republic in 2003. Date of larvae collection:
August 25 – December 1, 2003. Date of pupae observations: August 30 – October 2, 2003.
Date of adults observations after overwintering: May 10 – May 20, 2004.
Locality
SLOVAKIA
Brezová pod Br.
Nitra
Veľký Krtíš
CZECH REPUBLIC
Blatnička
SUM
Number of collected
larvae (ON)
Number of
collected pupae (SV)
% of parasitization
600
1500
250
19
1
27
3.16 %
0.06 %
10.8 %
5000
7350
50
97
1.00 %
1.32 %
Table R5.2. Parasitization of Ostrinia nubilalis (ON) larvae caused by Sympiesis viridula
(SV) at four localities of Slovak and Czech Republic in 2004. Date of larvae collection: July
23 – November 5, 2004. Date of pupae observations: September 23, 2004. Date of adults
observations after overwintering: - .
Localities
SLOVAKIA
Brezová pod Br.
Nitra
CZECH REPUBLIC
Blatnička
SUM
189
Number of
collected larvae (ON)
Number of
collected pupae (SV)
% of parazititation
1514
930
0
0
0%
0%
4914
7358
8
8
0.16%
0.16%
5.2.2. Lydella thompsoni
Table 5.3. Parasitization of the Ostrinia nubilalis (ON) larvae caused by Lydella thompsoni
(LT) at four localities of Slovak and Czech Republic in 2003. Date of larvae collection:
August 25 – December 1, 2003. Date of pupae observations: September 9 – October 2, 2003.
Date of adults observations after overwintering: March 20 – April 20, 2004.
Locality
SLOVAKIA
Brezová pod Br.
Nitra
Veľký Krtíš
CZECH REPUBLIC
Blatnička
SUM
Number of
collected larvae
(ON)
Number of
emerged pupae
(LT)
% of parasitization
Date when the first
pupae were found
(LT)
600
1500
250
2
53
41
0.33 %
3.53 %
16.4 %
9.9.2003
25.9.2003
2.10.2003
5000
7350
18
114
0.36 %
1.55 %
22.9.2003
Table 5.4. Parasitization of the Ostrinia nubilalis (ON) larvae caused by Lydella thompsoni
(LT) at three localities of Slovak and Czech Republic in 2004. Date of larvae collection: July
23 – November 5, 2004. Date of pupae observations: July 27 – September 10, 2004. Date of
adults observations: Brezová pod Bradlom September 12, 2004; Nitra July 28 – September 1,
2004; Blatnička September 3 – September 10, 2004.
Locality
SLOVAKIA
Brezová pod Br.
Nitra
CZECH REPUBLIC
Blatnička
SUM
190
Number of
collected larvae
(ON)
Number of
emerged pupae
(LT)
% of parasitization
Date when the first
pupae were found
(LT)
1514
930
1
10
0.06%
1.07%
10.9.2004
27.7.2004
4914
7358
3
14
0.06%
0.19%
2.9.2004
5.2.3. Microgaster tibialis
Table 5.5. Parasitization of the Ostrinia nubilalis (ON) larvae caused by Microgaster tibialis
(MT) at four localities of Slovak and Czech Republic in 2003. Date of larvae collection:
August 25 – December 1, 2003. Date of pupae observations: September 9 – September 12,
2003. Date of adults observations after overwintering: April 27 – April 28, 2004.
Number of
collected larvae
(ON)
Number of
collected pupae
(MT)
% of parasitization
Date when the first
pupae were collected
(MT)
600
4
0.66 %
10.9.2004
Nitra
1500
0
0%
9.9.2004
Veľký Krtíš
CZECH REPUBLIC
Blatnička
SUM
250
0
0%
5000
7350
3
7
0.06 %
0.09 %
Locality
SLOVAKIA
Brezová pod Br.
12.9.2004
Table 5.6. Parasitization of the Ostrinia nubilalis (ON) larvae caused by Microgaster tibialis
(MT) at three localities of Slovak and Czech Republic in 2004. Date of larvae collection: July
23 – November 5, 2004. Date of pupae observations: September 23 – September 28, 2004.
Date of adults observations after overwintering: -.
Locality
SLOVAKIA
Brezová pod Br.
Nitra
CZECH REPUBLIC
Blatnička
SUM
191
Number of
collected larvae
(ON)
Number of
collected pupae
(MT)
% of parasitization
Date when the first
pupae were collected
(MT)
1514
17
1.12%
28.9.2004
930
0
0%
0
4914
7358
7
24
0.14%
0.32%
23.9.2004
5.2.4. Sinophorus turionus
Chahrt 5.7. Parasitization of the Ostrinia nubilalis (ON) larvae caused by Sinophorus turionus
(ST) at four localities of Slovak and Czech Republic in 2003. Date of larvae and pupae
collection: August 25 – December 1, 2003. Date of adults observations after overwintering:
March 20 – March 28, 2004.
Locality
SLOVAKIA
Brezová pod Br.
Nitra
Veľký Krtíš
CZECH REPUBLIC
Blatnička
SUM
Number of
collected larvae
(ON)
Number of
collected pupae
(ST)
% of parasitization
Date when the first
pupae were collected
(ST)
600
1500
250
1
4
3
0.16 %
0.26 %
1.2 %
3.9.2003
1.10.2003
2.10.2003
5000
7350
9
17
0.18 %
0.23 %
4.10.2003
Table 5.8. Parasitization of the Ostrinia nubilalis (ON) larvae caused by Sinophorus turionus
(ST) at three localities of Slovak and Czech Republic in 2004. Date of larvae collection: July
23 – November 5, 2004. Date of pupae observations: October 6 – October 12, 2004. Date of
adults observations after overwintering: -.
Locality
SLOVAKIA
Brezová pod Br.
Nitra
CZECH REPUBLIC
Blatnička
SUM
192
Number of
collected larvae
(ON)
Number of
collected pupae
(ST)
% of parasitization
Date when the first
pupae were collected
(ST)
1514
930
4
0
0.26%
0%
6.10.2004
0
4914
7358
1
5
0.02%
0.06%
12.10.2004
5.3. Microsporidian infection of Ostrinia nubilalis
The presence of microsporidian infection in Ostrinia nubilalis was checked in autumn period
2003, 2004 and 2005, when larvae of O. nubilalis at chosen locations have been collected and
analysed for Nosema pyrausta spores presence (tables R6.1. –R6.3. ). After positive match of
spores of N. pyrausta these have been measured (table R.6.4.). In all three years of
observation the same area of country has been checked and positive presence match was not
observed in each ear. Based on three years study location Brezová pod Bradlom was found as
positive for 2 years – year by year, but the infestation was weak – only 1 larvae in 2003 and 4
larvae in 2004 were positive to spores presence from 20 collected larvae. Strong infection was
observed in location Vrbové, when in 2005, 16 larvae from 20 collected were positive to
spores presence, but there was only 2 larve found as positive in 2003 and no observation in
2004 at the same locality. Based on the results only 1 year positive findings were registered
at locations Dechtice in 2004 – 2 positive larvae from 20 collected and Hlohovec, Trstín,
Drahovce where 1 positive larva was observed from 20 collected larvae per each location and
Dubovany 2 positive larvae from 20 collected in 2005.
The strongest infestation was registered at location Blatnička (CZ), where 19 larvae were
positive to spores presence from 20 collected in 2003 and 17 larvae in 2004, even there is
third year observation absence in 2005 the estimation of this year spores presence is on the
level of years 2003 and 2004.
Table R6.1. Infection of the Ostrinia nubilalis larvae (ON) caused by Nosema pyrausta at 15
locations of Slovak and Czech Republic in autumn 2003.
Date of (ON) collection
Number of (ON)
collected larvae
Number of
infected larvae
SLOVAKIA
Boleráz location1
Boleráz location 2
Brezová pod Bradlom
Dechtice
Naháč
Paderovce
Topoľčany
Trnava
Trstín
V.Kostoľany location1
V.Kostoľany location 2
Vrbové location 1
Vrbové location 2
Žlkovce
CZECH REPUBLIC
20.10.2003
20.10.2003
5.9.2003
27.10.2003
27. 10 2003
19.10.2003
8.10.2003
27.10.2003
27.10.2003
19.10.2003
19.10.2003
19.10.2003
19.10.2003
19.10.2003
20
20
20
20
20
20
20
20
20
20
20
20
20
20
0
0
1
0
0
0
0
0
0
0
0
1
1
0
Blatnička
12.10.2003
20
19
Location
193
Table R6.2. Infection of the O. Nubilalis larvae (ON) caused by Nosema pyrausta at 11
locations of Slovak and Czech Republic in autumn 2004.
Location
SLOVAKIA
Boleráz
Brezová pod Bradlom
Dechtice
Košariská
V.Kostoľany location 1
V.Kostoľany location 2
Madunice
Šterusy
Piešťany
Trnava
CZECH REPUBLIC
Blatnička
Date of (ON) collection
Number of (ON)
collected larvae
Number of
infected larvae
20.10.2004
20.9.2004
19.10.2004
19.10.2004
19.10.2004
19.10.2004
19.10.2004
19.10.2004
20.10.2004
20.10.2004
20
20
20
20
20
20
20
20
20
20
0
4
2
0
0
0
0
0
0
0
20.9.2004
20
17
Table R6.3. Infection of the O. Nubilalis (ON) larvae caused by Nosema pyrausta at 10
locations of Slovakia in autumn 2005.
Location
SLOVAKIA
Hlohovec
Vrbové
Trstín
J. Bohunice location 1
J. Bohunice location 2
Dubovany
Rakovice
Drahovce
Brezová pod Bradlom
Naháč
Date of (ON) collection
Number of (ON)
collected larvae
Number of
infected larvae
8.11.2005
8.11.2005
8.11.2005
20.1.1900
20.1.1900
20.1.1900
20.1.1900
20.1.1900
20.1.1900
20.1.1900
20
20
20
20
20
20
20
20
20
20
1
16
1
0
0
2
0
1
0
0
Table R6.4. Size of Nosema pyrausta spores originated from different localities of Slovakia
and Czech Republic. The differences among size of spores originated from localities were not
significantly different (P > 0.05, Tuckey multiple range test). (1) – locality, (2) – measurement,
(3)
– spores size, (4) – average, (5) – lenght, (6) – wide.
Localities(1)
Measurement(2)
Dechtice
Length(5)
Width(6)
Length
Width
Length
Width
Vrbové
Blatnička
194
Size of spores (μm)(3)
Mean(4) ± S.D.
4.15±0.4805
2.10±0.1042
4.18±0.1574
2.01±0.0884
4.60±0.7421
2.12±0.1059
Min - Max
2.9 – 5.1
1.6 – 2.6
3.5 – 4.8
1.6 – 2.5
3.1 – 6.0
1.5 – 2.6
5.4. Influence of microsporidian infection caused by Nosema pyrausta from
Slovakia on populations of Ostrinia nubilalis from various countries
Influence of microsporidian infection has been evaluated on various Ostrinia nubilalis
populations in laboratory conditions. Obtained and calculated structure results are registered
in table 61., partial bionomy of populations observations are showed in tables 62. – 72. – in
appendix.
Based on results which were obtained in present test when larvae were kept in laboratory
conditions, temperature 25±1°C, relative air humidity 80%, fotoperiod 16:8. In German (1)
population, from choosen 50 larvae for each tested group, only 22 pupae from un-infected
population were observed, what represents 44% and 29 pupae from infected population, what
represents 58%. In case of moths emergence from un-infected population, 100% of adults
have been observed, what represented 10 males (45%) and 12 females (55%). Moths
emergence from infected population reached only 19 adult moths, what represents 66% of 29
emerged pupae. There was 11 males (58%) and 8 females (42%) noticed from 19 adults.There
was differences in egg clusters noticed as well. Females from infected population produced 19
egg masses and 30 egg masses were noticed from un-infected population. In second testing
population German (2) from 50 selected larvae in each tested group only 25 pupae in uninfected population, what represents 50% and 23 pupae from infected population, what
represents 46%, were observed. In case of adult moths emergence only 23 moths from 25
pupae in un-infected population, what represents 92% were observed. Infected population
reached 100% of adult moths emergence from 23 pupae. Proportion beween males in females
in un-infected population represents 16 males (70%) and 7 females (30%) from 23 adults.
Infected population proportion represents 12 males (52%) and 11 females (48%). 50 egg
masses were observed in un-infected population, females in infected population laid only 34
egg masses.
Population Slovakia*Romania reached similar results as first tested Aachen populations. In
case of pupae observation, 49 (98%) of pupae in un-infected population and 24 pupae (48%)
in infected population were observed. 100% of un-infected pupae hatched and 28 males
(57%) and 21 females (43%) of adult moths were observed. Infected population was weaker,
when only 24 pupae were observed from 50 infected larvae, what represents only 48%. Males
from un-infected population represent 28 moths (57%) and females represent 21 moths (43%).
Infected population adults represent 5 males (38%) and 8 females (62%). There was also huge
differences noticed between egg clusters of un-infected and infected population, when in uninfected population 27 egg masses and 5 egg masses in infected population were observed.
Pure Slovakia population was the weakest in case of whole dynamics. Only 19 pupae (38%)
of un-infected population and 13 pupae (26%) of infected population were observed. There
were only 4 adult females observed in un-infected population, what represented 21% of adults
from 19 pupae. 4 males (80%) and only 1 female (20%) were observed in infected population.
No egg masses were noticed in both un-infected and infected populations.
Austrian population was characterized by 40 pupae (80%) observed in un-infected population
and 38 pupae (76%) from infected population. Almost all pupae from un-infected population
hatched, when 39 adult moths (98%), 19 males (49%) and 20 females (51%) were observed.
In infected population only 23 adult moths (61%), 11 males (48%) and 12 females (52%)
were observed. Un-infected population females laid 32 egg masses, infected population
females laid 23 egg masses. There was Serbian population tested as last one. Obtained results
were similar to Slovakian ones. There was 34 pupae (68%) observed in un-infected
population and only 19 pupae (38%) from infected population. Un-infected population
represented 100% adult moths in which there were 18 males (53%) and 16 females (47%).
195
From 19 pupae of infected population 7 males (70%) and 3 females (30%) were observed. No
egg masses were noticed in both populations.
Table R7.1. Bionomy of Ostrinia nubialis originated from different regions of Europe after
infection with spores of Nosema pyrausta. In each experiment there were used 50 first instar
larvae. Experiment was organized at 16:8 hours in light:dark, 25°C and 80 % of air relative
humidity.
Origin of population
Finding
N.
pyrausta
Germany
1
Lab22
Germany
2
Lab23
Slovakia
(natural)
Number of pupae eclosed
No
Yes
22
29
25
23
Number of males emerged
No
Yes
10
11
Number of females emerged
No
Number of adults emerged
Number of egg clusters laid
Average time for pupal
eclosion (days)
Average time for male
emergence (days)
Average time for female
emergence (days)
Average time for adult
emergence (days)
Average time for egg laying
(days)
Austria
(lab6)
Serbia
(natural)
19
13
Slovakia
(natural)
x
Romania
(Lab11)
49
24
40
38
34
19
16
12
0
4
28
5
19
11
18
7
12
8
4
21
20
16
Yes
8
11
1
8
12
3
No
22
24
4
49
39
34
Yes
19
23
5
13
25
10
No
19
50
0
27
32
0
Yes
30
34
0
5
23
0
No
33.36
27.08
20.74
31.31
31.68
28.68
Yes
31.17
29.3
24.46
30.04
33.53
33.58
No
41
31.88
0
35.89
37.89
34.67
Yes
39.82
35.33
27.5
34.6
38.45
35.71
No
41.58
31.86
27
35.14
38.35
35.06
Yes
38.5
32.92
31
33.88
41.08
35.67
No
41.45
31.87
29
35.57
38.13
34.85
Yes
36.79
35.74
30.6
34.15
36.64
35.7
No
43.79
36.46
30.63
31.63
41.31
0
Yes
41.7
40.62
24.46
42.8
40.26
0
Average weight of fifth
instar larvae ((g)
No
0.14
-
0.09
0.1
0.08
0.09
Yes
0.13
-
0.08
0.06
0.09
0.08
Average weight of pupae (g)
No
0.07
-
0.07
0.07
0.07
0.07
Yes
0.07
-
0.06
0.08
0.07
0.07
196
6. DISCUSSION
6.1. O. nubilalis population and infestation in Slovakia.
O. nubilalis populations, like those of other insect species, fluctuate indensity from year to
year (Chiang, 1961). Chiang and Hodson (1972) suggested, that density independent factors
are primarily responsible for such fluctuations in populations of this pest. Agricultural
practices, natural enemies, and varied climatic factors are commonly viewed as regulating
agents (Barlow et al., 1963) what was also confirmed in 4 years study 2006 - 2009. Young
larvae are extremely sensitive. A slight injury of any kind or a short deprivation of proper
food is sufficient to cause a very high mortality among the young larvae (Anonymous, 1928).
Most caterpillars do not survive more than a few days, but succumb to desiccation, predatory
insects, drowning in rainwater. There are many reports that weather influences O. nubilalis
survival. Heavy precipitation during egg hatch, for example, is sometimes given as an
important mortality factor. Low humidity, low nighttime temperatures, and heavy rain and
wind are detrimental to moth survival and oviposition. However, during a 10-year, 3-state
study, (Sparks et al.,1967) reported no consistent relationship between weather and survival.
According to Showers et al., (1976, 1980) environmental conditions can have a major impact
on the size of insect population (Showers et al., 1976, 1980). O. nubilalis, is the most
important maize pest in Slovakia and is responsible for considerable yield loss each year
(Cagáň, Grenčík, 1990). On the basis of their observations in 1991-1993 was found, that in
Slovakia there are the locations with permanent high ocurence of the O. nubilalis. In western
Slovakia were these locations in hilly region with altitute 170-220 m and in eastern Slovakia
also in plains with the altitude nearly 100 m. This fact was confirmed as well in conducted
present study, when all locations with highest average percentage damages are situated in
west part of Slovakia. According to Cagáň and Grenčík (1990) average yearly temperature at
the locations with high occurrence of the O. nubilalis was in western Slovakia 9-9.4 °C and in
eastern Slovakia 9-9.7 °C. The highest occurrence of the pest was found at the locations with
nearly 600 mm rainfall per year. The area with the highest occurrence of the O. nubilalis
corresponded to the warm and moderate dry climatic area (the number of summer days in year
above 50, moisture index acc. (Koncek, 1980; Cagan et al., 1995).
All years damages especially in south part of Slovakia were influenced by second generation
of pest. Second generation potencial was first time observed by Barabas et al., (1985). Based
on his study done in 1973 – 1983 he indicated the occurrence of a partial 2nd generation
especially in years with above average temperatures especially when these overreached
average daily temperature in May – August 19°C. Cagan (1998 c) confirmed pupal stages in
observed stalks what indicated the development of the second generation adults of the pest.
This was largely related to temperature. Minimum daily temperatures in July 1994 never
dropped below 12 °C (Cagan, 1998c). Based on obtained results especially in locality Veľký
Meder in observations 2006 – 2009, there is a hint of second generation infestation. The
presence is obvious especially from strong damages on maize ears and young larvae feeding
on developed and nearly matured ears in September, even the status and confirmation of the
second generation was not point of observation.
Studies on infestation made by Cagan and Grencik (1990) of 5 maize hybrids by O. nubilalis
carried out in 7 localities in the former Czechoslovakia in 1986-88 showed, that when the
percentage infestation in a stand was no higher than 80% the damage to the infested plants
was about the same. The average numbers of holes in the stems and of damaged ears per
infested plant increased only when infestation increased beyond this (Cagan Grencik, 1990).
Keszthelyi et al., (2002) conducted a study during 2001 near Somogyszil, Hungary on maize
hybrid DK471 to determine the effect of maize borer larvae on the weight and chemical
197
composition of maize ears and the effect of larval density per plant. An increase in larval
density caused a decrease in ear weight. In addition, larval damage and density significantly
affected ear weight and nutrient (i.e. raw protein, raw fat, and starch) content. The same
hybrid was checked in present sudy in 2006 at 7 locations, when average percentage damage
reached 21%, in 2007 at 12 locations and damaged reached 12.83% and in 2008 at 5 locations
with average percentage damage 22%. Based on observed data damages caused yield quality
and quantity losts, which also corresponded with whole pest infestation in mentioned years.
There was no connection between hybrid and O. nubilalis infestation.
6.2. Species spectrum of the O. nubilalis parasitoids.
Parasites of Ostrinia nubilalis have been described by various writers. To find natural
enemies of O. nubilalis is one way of natural control. Numerous studies were conducted
under laboratoy and natural conditions to identify parasitic wasps with the potential to control
pest insects (Stuart, Burkholder, 1991). There are also some parasites which attack corn borer
eggs. Overall, parasites have a low impact on the population. There is some evidence that the
level of predatory insects in maize fields can be influenced by farm management practices.
The use of insecticides, including those applied at planting, reduces the predator population.
In no-till systems the level of predators has been reported to increase.
Based on the two years study, in the year 2003 the parazititation, when all collected
parasitoids were counted, from 7350 collected larvae reached 3.19% and in the year 2004
from 7358 reached 0.69%. There were differences between the distribution of parasitoids at
selected localities. In the year 2003 and 2004 the highest level of parazititation was recorded
in the conditions of Blatnička and Brezová pod Bradlom. These localities have similar
weather conditions, geografical location and the country is more hilly than locality Nitra or
Veľký Krtíš is. These data were focused on S. viridula and M. tibialis. This result was
confirmed in the year 2003, when 47 pupae from Slovakia and 50 pupae from Czech Republic
were collected. Next year was the right opposite and only 8 pupae In Czech Republic were
collected. S. viridula was first mentioned in 1927, when Oglobin (cit. Parker, Smith, 1933)
bred a colony of this species from O. nubilalis from maize in Czechoslovakia. The next
mention about this chalcid in Slovakia was from Bokor and Cagáň (1997). It is not clear, how
many generations can emerge in conditions of Slovakia. During the research in 2003 and 2004
only pupae of this chalcid in the autumn were found. Parker and Smith (1933) proved three
generations on the corn borer in Po Valley. The first and second generation was occurred in
hemp and Agostino maize, on the first brood of the host, while the third (and very propably a
partial fourth) generation of S. viridula was occured in both of the Agostino and the
Cinquantino maize, but upon the second generation of the host. There is also another
important question if is possible to emerge S. viridula on the different plants exept maize.
Parker and Smith (1933) recorded some individuals on Polygonum or Arthemisia. These
plants are also known as the second host plants for O. nubilalis. So it is important to confirm
or deny this fact – if is possible to find single S. viridula on the different host plant or to find
O. nubilalis with S. viridula on the different host plant exept maize, in conditions of Slovakia.
There is an important fact, that there are very limited or no source data characterizing S.
viridula occurrence in Slovakia or former Czechoslovakia.
Parazititation of M. tibialis in the years of research 2003 and 2004 increased, but from the
number of collected O. nubilalis larvae this parazitation did not reach the number which could
influenced the the population density of O. nubilalis. Bokor and Cagáň (1999) were interested
in this parasitoid too. From their observations in 1993 the parazitation in Blatnice (CZ) was
(2.95%), (from 392 collected larvae), 1994- (2.05%), (1653 collected larvae) and in year 1995
– (1.83%), (from 1707 collected larvae). The parazititation which was observed in years 2003
198
and 2004 was quite different and the % of parazititation reached only (0.06%), (from 5000
collected larvae) in 2003 and (0.14%), (from 4914 collected larvae) in 2004. Research from
years 2003 and 2004 confirmed basic biology which was observed by Bokor and Cagáň
(1999) when the parasitoids emerged during April and the cocoons were collected in the same
period as in research 2003 and 2004.
L. thompsoni was the most abundant in the warmer locality Nitra – Slovak republic, but at
this locality almost none pupae of S. viridula were not found. Also the occurrence of L.
thompsoni in locality Blatnička was low. This could be influenced by the fact that, L.
thompsoni is focused on the warmer localities. Results obtained in research 2003 and 2004
were similar to the results of the work of Cagáň, et al,. (1999). The level of occurrence of the
alternative host could be high in the locality Nitra, where the parasitation of L. thompsoni was
the highest and this locality is siutable (enough warm) for another population on alternative
host. Dudich (1928), Hergula (1929) and Cagáň (1999) in their studies confirmed, that the
adults of L. thompsoni hatched very early in the spring, but they did not attack O. nubilalis
larvae during the period of hibernation, but they could be able to create one population on the
alternative host. Brezová pod Bradlom is the locality which is geografically between the Nitra
and Blatnička (in weather conditions closer to Blatnička) and the presence of the parasitoids
was also between the results of Nitra and Blatnička, what was confirmed in the results of year
2004. In the year 2003 the locality Veľký Krtíš reached results, which were similar to the
results of Nitra, but there was difference in occurrence of S. viridula in this locality, which
was much more higher than in Nitra and Brezová pod Bradlom and was relatively close to the
results of Blatnička.
In the case of S. turionus, in both years 2003 and 2004 the first pupae were found at the end of
September and in the first week of October. These data corelated with the results of the work
of Cagáň and Bokor (1998), when the first pupae were found in September 29 and the last
pupae were found until the beginning of December. In research 2003 and 2004 the first pupae
were found on 3.9. 2003 in locality Brezová pod Bradlom and 6.10. 2004 on the same
locality. Our findings in 2003 and 2004 also showed, that S. turionus was not a parasitoid,
which could influenced the population density of O. nubilalis larvae. The number of collected
pupae is similar in both years, but in 2004 temperate increase was observed in two localities –
Blatnička and Brezová pod Bradlom.
During this study in both years, the whole level of parazititation decreased, this result could
be influenced with weather conditions, in both years the spring was cold and wet, summer
came later and was dry and warm, autumn was quite warm. Dittrick and Chiang (1982) in
their work confirmed that the temperature influenced the emerge of parasitoids from each
host. Their results showed a dramatic increase from 20 to 25 ºC. The ability of emerged
parasitoids to reach the pupation stage succesfully, was affected significantly by temperature,
with an optimum of 25ºC. These conditions were suitable for L. thompsoni (locality Nitra Slovakia 2003 - 2004) and the level of parasitation should grow up, but the result was
opposite. Beside the physical conditions, parasitoids need some alternative weeds, growing
beside to the maize plants. The weeds are important for parasitoids as the source of honey
which is important for parasitoids to get mature. Selected localities which were tested in 2003
and 2004 exept locality Brezová pod Bradlom were without weeds around the maize field or
these were presented only in some small areas and this fact could also influenced the result.
Puvuk and Stinner (1992) tested parazitism of second generation, O. nubilalis larvae. Neither
broadleaved nor grassy weeds had significant influences on parasitization of larvae during the
study. Parazitism was positively correlated with host density (number of larvae per plant) in
the maize-broadleaved weed community.
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6.3. Microsporidian infection of the European corn borer
Phase-contrast microscope is usually used for examinations of Nosema pyrausta spores
(Andreadis, 1984; Siegel et al., 1986b). In these studies, both phase-contrast and light
microscopy was used. This confirmed data of the other authors on identification of N.
pyrausta spores. Paillot (1928) stated that it is not possible to distinguish between parasitized
and healthy O. nubilalis larvae according to external macroscopic symptoms. The
identification of N. pyrausta infection is only possible by direct observation of spores in
tissues of host. N. pyrausta spores were observed in Malphigian tubules, digest system, and
spinning glands of larvae. Similarly Cossentine and Lewis (1988) have also found the spores
in the same organs. Observed spores had oviform or oval shape, what corresponded to a shape
listed also in other papers (Kramer, 1959a; Lipa, 1977; Sidoe et al., 1983). The size of N.
pyrausta spores have been investigated by several authors and different dimensions were
presented (e.g. 3.2-4.7 m x 1.8-2.6 m (Kramer, 1959a), 3.0-6.9 m x 1.4-2.5 m (Lipa,
1977), 1.79-6.25 m x 1.79-4.46 m (Sidor et al., 1983). The size of spores found in our
observations (2.9-6.0 m x 1.5-2.7 m) was the most similar to the data presented by Lipa
(1977).
The protozoan infection of O. nubilalis larvae can be caused by N. pyrausta and Thelohania
ostriniae (= Vairimorpha necatrix (Lewis et al., 1982)). T. ostriniae was for the first time
observed and described by Lipa (1977). These two species could be distinguished by locality
of spores in body of host larvae, by shape and size of spores. T. ostriniae attacks particularly
fat tissue of host larvae and spores are shorter, both endings are equally oval (Lipa, 1977;
Sidor at all., 1983). T. ostriniae was not observed in our experiments.
According to this knowledge, in last 60 years there is almost no information concerned to
microsporidian infections of the O. nubilalis in Europe. Microsporidian infection was
investigated only in Vojvodina (former Serbia) where Sidor et al. (1983) found two
microsporidian species - N. pyrausta and Thelohania ostriniae. First records of the N.
pyrausta occurrence in Europe originate from the studies of Thompson and Parker (1928) and
Paillot (1928) who found infected O. nubilalis larvae in Italy, France and in Hungary.
Lipa (1977) stated, that larvae collected on different localities in Poland were not infected by
N. pyrausta spores. He also did not find the parasite at locality Wroclaw in Poland.
In North America, the percentage of infection was 60 and 80 in Delaware (VanDenburgh,
Burbutis, 1962), 0-78 % in Massachusetts (Peairs, Lilly, 1974), 5.9-76.2 % in Conecticut
(Andreadis, 1982), and 4.9-21.4 % in Ontario (Laing, Jaques, 1984). There was found regular
occurrence of N. pyrausta in western Slovakia (locality Dechtice) and percentage of infected
larvae at this locality achieved 0 - 10 %. The second area with a regular occurrence of N.
pyrausta was in district Uherské Hradiště – Blatnička with infection rates between 85.0 and
95.0 %. Both areas with regular occurrence of N. pyrausta had very high infestation of the
maize plants by O. nubilalis. Hill and Gary (1979) reported that after O. nubilalis increased in
abundance and density during 16 years in Nebraska, the incidence of N. pyrausta infection
also tended to increase. Slovakian localities with high microsporidian infection of O. nubilalis
populations were situated in colder regions of maize growing. In these regions a very high
infestation of maize caused by O. nubilalis was found (Cagáň, 1993). High density of the host
seems to be very important factor which support the establishment of higher infection by
microsporidium. Andreadis (1982) determined significant positive linear correlation between
corn borer density and corn borer infection with N. pyrausta. High host density and long
period of its activity belong to the most important factors influencing spread of
microsporidian infection (Andreadis, 1986). These factors occurred particularly in areas with
two host generations per year. Hill and Gary (1979) also presented that high density in O.
nubilalis populations was fundamental condition for epizootic development of N. pyrausta.
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Done observations showed that localities with high microsporidian infection were situated in
areas with high O. nubilalis occurrence. Blatnička in Moravia and Dechtice in Slovakia are
areas with annual abundant pest occurrence (Lokaj, Marek, 1986; Cagáň, 1993). O. nubilalis
larvae infected by N. pyrausta were not found at localities with low density of pests.
The infection focuses were formed in places with high host occurrence in western Slovakia. In
spite of high O. nubilalis occurrence within east Slovakia, O. nubilalis larvae infected by
spores of N. pyrausta were found only in 1993 at locality Kráľovský Chlmec.
The observations in the north part of Trnava district (where location Dechtice is), showed that
infection did not spread from this area. This fact was confirmed by long-term observations.
Focus of the N. pyrausta highest occurrence seems to be situated around villages Dechtice and
Kátlovce. Infection has probably local character and microsporidian occurred only in certain
areas with specific microhabitat conditions (soil properties, weather conditions etc.). Even this
fact has been confirmed in studies made by Cagáň and Bokor, in present study, there was no
spores presence confirmed in 2003 check, only 2 positive larvae to spores presence were
observed in 2004 from 20 collected larvae. The presence of O. nubilalis larvae was abundant.
Microsporidian have only two ways for spread to further areas - with contaminated food or by
infected eggs (Madox, 1987, Solter et al., 2005). It means that only migrating O. nubilalis
adults can transmit the infection to a long distances. But, because the infection did not change
a lot in all investigated localities, O. nubilalis adults probably do not migrate long distances.
It also seems that the parasite do not change its properties, even Baker et al. (1994) and
Vossbrinck (2005) indicated that microsporidia have radiated into different hosts over
evolutionary time and molecular studies show that the genome is highly evolving (Slamovits,
2004). The results in tables 57 - 59 show a very low level of infestation by N. pyrausta in
conditions of maize fields in the west part of Slovakia. Results from locality Blatnička in
Czech Republic are different. This locality is known as locality, where is maize planted very
often and maize can be planted on the same field year by year, what causes very good
conditions for O. nubilalis larvae, as the main source for microsporidian spores, as it has been
mentioned before. Also the infestation of O. nubilalis larvae is much higher. The infestation
of the maize plants by the O. nubilalis was usually higher than 2 larvae per plant, what is very
good for horizontal and vertical transmission. In Slovakia maize usually used to be grown at
the same field after 2-3 years, in nowadays this practice has been changed. Changing weather
condiditions could probably influence the occurrence of the pest also.
The distribution of microsporidian spores could be also enhanced by higher occurrence of
natural parasitoids of O. nubilalis larvae. Some of these parasitoids are responsible for better
transmission of microsporidian spores and the measure of parasitoids occurrence is much
more higher in Czech Republic, locality Blatnička, when compare to the localities in
Slovakia. Andreadis (1982) and Siegel et al., (1986) also observed that the parasitoid
Macrocentrus grandii, was responsible for some horizontal spread of the microsporidian
disease. Mobile parasitoids could seek out and infect otherwise uninfected borers as well as
transfer the pathogen from regions of high infection to regions of low infection within a maize
field. The localities in Slovakia are relative close to Blatnička in Czech Republic and the
transmission of the spores by mobile parasitoids could be possible, but there is natural border
Biele Karpaty mountains which can protect this natural transmission.
Large numbers of N. pyrausta spores were observed within the Malpighian tubules, and only
when infestation of the larvae was very high, the spores were found also in midgut. The size
of spores from larvae collected in localities Dechtice, Vrbové and Blatnička, where this
protozoan was observed regularly as it is summarised in Table 60. The spores were 2.9 – 6.0
μm in length and 1.5 – 2.7 μm in width. Average width of spores originated from all localities
was approximately the same (ca 2 µm). Average length of spores originated from locality
Blatnička was 4.6 μm and that from other three localities 4.15 μm (Dechtice), 4.18 μm
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(Vrbové), and 4.07 μm respectively. The differences among the localities were not significant
(P>0.05).
6.4. Influence of microsporidian infection caused by Nosema pyrausta from Slovakia on
populations of O. nubilalis from various countries.
Nosema pyrausta, an entomopathogenic microsporidium, is an important population regulator
of the European corn borer, Ostrinia nubilalis. Paillot (1927) first described N. pyrausta from
European corn borers collected in France, and the pathogen was first found by Steinhaus
(1951) in the United States in larval European corn borers from the Midwest. By 1957 the
microsporidium was present in Illinois, and Kramer (1959) noted that it could be an important
biological mortality factor of the corn borer (Siegel et al., 1987). N. pyrausta was also
described from O. nubilalis in Hungary in 1927 and from O. nubilalis in IA in 1950 (Lewis et
at.l, 2009). Pathogen affects the basic biology of O. nubilalis by slowing larval development,
reducing percentage pupation, and decreasing adult longevity, oviposition and fecundity.
Infections are maintained in a population by vertical and horizontal transmission. Success of
vertical transmission depends on intensity of infection. Horizontal transmission is dependent
on stage of larval (Lewis ate al., 2009). Similar conclusions have been noticed and studied by
various author before as they have concluded that N. pyrausta is a widespread microsporidian
pathogen which produce chronic infections that are frequently panzooic in the O. nubilalis,
slows larval developmental rate, increases larval mortality (Zimmack et al., 1954; Zimmack,
Brindley, 1957; Kramer, 1959; Siegel et al.,1986b; Solter et al., 1990), (VanDenburgh,
Burbutis, 1962; Peairs, Lilly, 1974; Indels et al., 1976; Hill, Gary, 1979, cit. Andreadis,
1981), reduces fecundity and longevity in infected adults (Windels et al., 1976; Bruck et al.,
2001) and causes increase of oxygen consumption throughout the life cycle of infected O.
nubilalis larvae (Lewis et al., 1971). Sajap and Lewis (1988) exposed O. nubilalis larvae in
5th instar, to 100, 200, 400, and 800 N. pyrausta spores/mm2 diet surface for 48 hr. Infections
were evident in the reproductive tissues in all insects 7 days after exposure, regardless of the
stadium in which and the dosages of spores to which the larvae were exposed. The
microsporidian spores were found infecting the epithelial layers and stroma cells of the larval
ovarian tissues. In larvae that had a more intense infection, the germ cells were also infected.
The microsporidian spores remained in the infected tissues, and infections progressed into
adult reproductive tissues, where trophocytes and oocytes enveloped in follicles were
infected. Consequently, these infections resulted in the transovarial transmission of the
microsporidium (Sajap, Lewis, 1988). Model of expose of N. pyrausta spores in diet surface
was used in test to secure young larvae infection. Status of infection was checked 10 days
after artificial infection and confirmed by light – microscopy. Transovarial infection in first
generation larvae was confirmed also by Siegel et all., (1988). Later on the body parameters
as larvae body weight and lengt was check and compared between infected and un-infected
populations as it is noticed in table 61. and appendix tables 62. - 72. Based on obtained results
there were no differences observed between infected and un-infected O. nubilalis larvae
weight and length. Bruck et al., (2001) made a monitoring of N. pyrausta-infected and
noninfected O. nubilalis larvae which were maintained in two different temperature regimes.
The first regime allowed females to oviposit under optimum conditions (27°C, 65% RH, 16:8
(L:D)), while females in the second regime were held initially under the same humidity and
light conditions, but a constant temperature of 16°C for 1 week after which they were
transferred to optimum ovipositional conditions. Studies were performed initially with O.
nubilalis populations and later with individual mating pairs. In studies with O. nubilalis
populations, the mean number of eggs laid per female under optimum conditions was 660,
while N. pyrausta-infected females held initially at 16°C laid 116 eggs per female. In studies
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with individual mating pairs, N. pyrausta infection reduced egg production per female 53 and
11% in the 16 and 27°C temperature regimes, respectively, compared to noninfected females
under optimum conditions. Exposure to 16°C temperatures early in the ovipositional period
had a more profound impact on reducing egg production in N. pyrausta-infected than
noninfected O. nubilalis (Bruck et al., 2001). Based on results which were obtained in present
test when larvae were kept in laboratory conditions, temperature 25±1°C, relative air
humidity 80%, fotoperiod 16:8, we can conclude some changes in life dynamics. There was in
Germany (1) population some differences noticed between infected and un-infected
populations. From choosen 50 larvae for each tested group, only 22 pupae from un-infected
population were observed and 29 pupae from infected population. In case of moths emergence
from un-infected population, 100% of adults have been observed, what represented 10 males
and 12 females. Moths emergence from infected population reached only 19 adult moths,
what represents of 29 emerged pupae. There was 11 males and 8 females noticed from 19
adults. There was differences in egg clusters noticed as well. Females from infected
population produced 19 egg masses and 30 egg masses were noticed from un-infected
population. In second testing population Germany (2) from 50 selected larvae in each tested
group only 25 pupae in un-infected population and 23 pupae from infected population were
observed. In case of adult moths emergence only 23 moths from 25 pupae in un-infected
population were observed. Infected population reached 100% of adult moths emergence from
23 pupae. Proportion beween males in females in un-infected population represents 16 males
and 7 females from 23 adults. Infected population proportion represents 12 males and 11
females (48%). 50 egg masses were observed in un-infected population, females in infected
population laid only 34 eg masses. Population Slovakia *Romania reached similar results as
first tested German populations. In case of pupae observation, 49 of pupae in un-infected
population and 24 pupae in infected population were observed. 100% of un-infected pupae
hatched and 28 males and 21 females of adult moths were observed. Infected population was
weaker, when only 24 pupae were observed from 50 infected larvae. Males from un-infected
population represent 28 moths and females represent 21 moths. Infected population adults
represent 5 males and 8 females. There was also huge differences noticed between egg
clusters of un-infected and infected population, when in un-infected population 27 egg masses
and 5 egg masses in infected population were observed.
Pure Slovakia population was the weakest in case of whole dynamics. Only 19 pupae of uninfected population and 13 pupae of infected population were observed. There were only 4
adult females observed in un-infected population from 19 pupae. 4 males and only 1 female
were observed in infected population. No egg masses were noticed in both un-infected and
infected populations. There was 40 pupae observed in un-infected population and 38 pupae
from infected population. Almost all pupae from un-infected population hatched, when 39
adult moths 19 males and 20 females were observed. In infected population only 23 adult
moths, 11 males and 12 females were observed. Un-infected population females laid 32 egg
masses, infected population females laid 23 egg masses. There was Serbian population tested
as last one. Results were similar to Slovakian ones. There was 34 pupae observed in uninfected population and only 19 pupae from infected population. Un-infected population
represented 100% adult moths in which there were 18 males and 16 females. From 19 pupae
of infected population 7 males and 3 females were observed. No egg masses were noticed in
both populations.
Windhel et al., (1976) in his study concluded that adult longevity, oviposition, fecundity and
fertility were adversely affected by infection with N. pyrausta. Also Siegel et al., (1986)
indicated that corn borer adults infected with N. pyrausta laid 33% fewer egg masses than
uninfected adults.
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Due to these results tested populations only partly confirmed that fecundity and oviposition
differences between un-infected and infected O. nubilalis population with N. pyrausta spores.
Oviposition and sum of egg masses were lower in infected population of Germany (2),
Slovakia *Romania and Austria. Sum of egg masses was higher in case of Aachen (1)
infected population. Slovakian and Serbian population did not result in oviposition, althought
the populations were infected or not. Windhel et al., (1976) concluded that reproduction of
infected moths was 39.3% lower than that of moths with no detectable infection, and heavily
infected moths had 52.0% lower reproduction. This conclusion were confirmed in Germany
(2), Slovakia *Romania and Austrian population. Solter at al., (2001) determined that infected
males mated as effectively as uninfected males and produced offspring, what represented
results obtained from Germany (1) population, where number of egg masses was higher in
infected population.
Even there were some differences indicated between un-infected and infected population,
average time for pupal eclosion, average time for male – female emergence and average time
for egg laying as they are mentioned in table 61. did not show a huge differences between life
cycle dynamics in un-infected and infected populations of O. nubilalis with N. Pyrausta
spores.
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7. SUMMARY
Occurrence and natural enemies of O. nubilalis was observed over 4 years study in Slovakia.
Based on obtained data there were calculated correlations between the pest infestation and the
presence of pathogens, or influence of conditions of locality, or influence of hybrid.
Correlation coefficients between the occurrence of O. nubilalis or H. armigera larvae and the
presence of maize pathogens during observations at selected locations in 2006, 2007, 2008
and 2009 showed that in some cases there were positive and significant correlations at some
locations in favourable years, but it was not usual case to found correlation between the pest
presence and the occurrence of pathogens.
Climatic factors can influence the density and status of infestation of the pest. The influence
of climatic conditions during years 2006, 2007, 2008 and 2009 to damages caused by O.
nubilalis larvae was registered as well. It was confirmed that there were location over
Slovakia, where are favourable conditions for the pest infestations and the presence of the
pest was registered regularly. From the selected locations under regular evaluation there were
Veľký Meder, Kalná nad Hronom, Čakajovce or Borovce. The highest damages of pest was
registered in years 2008 and 2009. The highest percentage of the damage was observed in
2008 at localities Kalná nad Hronom (40.67%), Veľký Meder (39.38%), Čakajovce (28.83%),
and Borovce (22.29%). In 2009, the highest percentage of damage was observed in Veľký
Meder (40.44%), Borovce (23.40%), Kalná nad Hronom (18.18%) and Čakajovce (16.00%).
Year 2006 and especially 2007 was the most un-favourable, but the damages were observed at the location Veľký Meder the damages were only on 15.38% of plants observed (Borovce
13.08% and Čakajovce 7.63%).
Over four years of the study more than 100 hybrids were checked to O. nubilalis presence and
correlation between the pest damage and hybrid were evaluated. Based on obtained data it
was concluded that, there is no significant evidence for correlation between maize hybrid and
infestation of the pest.
Natural enemies which included the parasitoids and protozoan Nosema pyrausta were closely
connected to O. nubilalis larvae. The most abundant parasitoids which were observed were
Sympiesis viridula (Thomson), Lydella thompsoni (Herting), Microgaster tibialis (Nees), and
Sinophorus turionus. In 2003, S. viridula parasitization achieved 1.32%. The parasitization of
L. thompsoni was 1.55%, M. tibialis 0.09%, and S. turionus 0.23%, respectively. In 2004, the
parasitization of S. viridula achieved 0.16%, L. thompsoni 0.19%, M. tibialis 0.32%, and S.
turionus 0.06% respectively. The differences were significant in each of observed parasitoid,
when two years were compared.
Nosema pyrausta, a protosoan causing chronic infection was closely connected with O.
nubilalis larvae. Usually it was observed at selected locations in the west part of Slovakia and
one location in Czech Republic. In three year period of the study, the highest and periodical
presence of it was confirmed at location Blatnička, where infection was well spread. From 20
collected larvae, 19 larvae were positive to spores presence in 2003 and 17 larvae in 2004.
Results from Slovakian locations did not follow results from the Czech Republic and infection
differences were registered over locations and years. Whole observed larvae infection was
low – just average of 2–3 infected larvae from sampling group of 20 collected larvae. The
protozoan pathogen was observed due hint of potential life cycle changes which are provoked
by pathogen presence. Bionomy of O. nubilalis originated from different regions of Europe
after infection with spores of N. pyrausta was not changed evidently. Despite of some
differences indicated between un-infected and infected populations, average time for pupal
eclosion, average time for male – female emergence and average time for egg laying did not
show significant differences between life cycle dynamics in un-infected and populations of O.
nubilalis infected with N. pyrausta spores.
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Výskyt a prirodzení nepriatelia vijačky kukuričnej – Ostrinia nubilalis boli pozorované počas
4 ročnej štúdie na Slovensku. Na základe získaných dát boli vyrátané korelačné koeficienty
medzi výskytom škodcu a prítomnosťou jeho parazitov, vplyvu podmienok prostredia lokality
a vplyvu hybridu kukurice. Korelačné koeficienty medzi výskytom húseníc vijačky
kukuričnej alebo mory bavlníkovej – Helicoverpa armigera a fytopatogénnymi hubami počas
pozorovaní na vybraných lokalitách v roku 2006, 2007, 2008 a 2009 potvrdili, že v niektorých
vybraných lokalitách a prípadoch boli potvrdené pozitívne a jednoznačné korelácie počas
klimaticky vhodných rokov, ale tieto korelácie nebolo bežné nájsť pravidelne medzi
prítomnosťou škodcov a výskytom fytopatogénnych húb.
Klimatické faktory môžu ovplyvniť hustotu a status výskytu škodcu. Vplyv klimatických
podmienok a poškodenie kukurice larvami vijačky kukuričnej boli hodnotené počas rokov
2006, 2007, 2008 a 2009. V rámci podmienok Slovenska boli potvrdené lokality s veľmi
priaznivými klimatickými podmienkami, kde bola pravidelne zaznamenávaná prítomnosť a
poškodzovanie rastlín škodcom. Z vybraných lokalít, ktoré boli pravidelne sledované to boli
Veľký Meder, Kalná nad Hronom, Čakajovce a Borovce. Najväčšie poškodenia húsenicami
vijačky kukuričnej boli zaznamenané v roku 2008 a 2009. Najväčšie percentuálne poškodenie
rastlín bolo pozorované v roku 2008 v Kalnej nad Hronom (40.67%), Veľkom Mederi
(39.38%), Čakajovciach (28.83%) a Borovciach (22.29%). V roku 2009, bolo najväčšie
percentuálne poškodenie rastlín pozorované vo Veľkom Mederi (40.44%), Borovciach
(23.40%), Kalnej nad Hronom (18.18%) a Čakajovciach (16.00%). Rok 2006 a najmä rok
2007 boli z hľadiska výskytu škodcu klimaticky najnepriaznivejšie, ale i napriek tomu boli
poškodenia húsenicami vijačky kukuričnej pozorované – vo Veľkom Mederi 15.38%
poškodených rastlín (Borovce 13.08% a Čakajovce 7.63%).
Počas 4 ročných pozorovaní bolo hodnotených viac ako 100 hybridov kukurice a prítomnosť
škodcu na týhto hybridoch. Zo získaných dát boli vypočítané korelačné koeficienty, na
základe ktorých nebol potvrdený priamy vzťah medzi výskytom škodcu – vijačky kukuričnej
a hybridom kukurice.
Medzi prirodzených nepriateľov vijačky kukuričnej patria parazity a prvok Nosema pyrausta,
ktorí sú úzko spätí s húsenicami škodcu. Z pomedzi najrozšírenejších parazitov, ktorí boli
pozorovaní patrí Sympiesis viridula (Thomson), Lydella thompsoni (Herting), Microgaster
tibialis (Nees), and Sinophorus turionus. V roku 2003 parazitácia húseníc vijačky kukuričnej
parazitom S. viridula predstavovala 1.32%, L. thompsoni 1.55%, M. tibialis 0.09%, a S.
turionus 0.23%. V roku 2004, parazitácia parazitom S. viridula predstavovala 0.16%, L.
thompsoni 0.19%, M. tibialis 0.32%, a S. turionus 0.06%. Rozdiely medzi parazitáciou
jednotlivými parazitmi boli výrazne rozdielne medzi jednotlivými parazitmi a medzi 2 rokmi
pozorovaní parazitácie.
Nosema pyrausta je prvok, ktorý spôsobuje chronickú infekciu húseníc. Prítomnosť tohto
prvoka bola pozorovaná na vybraných lokalitách v západnej časti Slovenska a jednej lokalite
v Českej republike. Počas 3 rokov pozorovaní bola najvyššia a pravidelná prítomnosť tohto
prvoka ptvrdená na lokalite Blatnička v Českej republike, kde bola infekcia húseníc dobre
rozvinutá. Z kontrolnej vzorky 20 húseníc, bolo 19 pozitívnych na prítomnosť prvoka N.
pyrausta v roku 2003, a 17 v roku 2004. Výsledky z pozorovaní v západnej časti Slovenska
nekorelovali s výsledkami z Českej republiky, kedy výrazné rozdiely boli medzi jednotlivými
lokalitami i počas 3 rokov pozorovaní. Celkové napadnutie húseníc bolo nízke, pozitívna
prítomnosť spór prvoka bola priemerne 2 – 3 infikované húsenice z 20 húseníc kontrolnej
vzorky. Vplyv prvoka N. pyrausta na populácie vijačky kukuričnej z rôznych európskych
populácií bol pozorovaný pre podozrenie na ovplyvňovanie vývojového cyklu a bionómie
škodcu. Bionómia škodcu z rôznych európskych populácií po infekcií prvokom nebola
výrazne zmenená. I napriek tomu však boli zaznamenané rozdiely medzi infikovanými a
neinfikovanými populáciami – priemerný čas vytvorenia kukiel, priemerný čas výletu
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samičiek a samčekov vijačky kukuričnej a priemerný čas kladenia vajíčok nepreukázali
jednoznačné rozdiely medzi dynamikou vývojového cyklu infikovaných a neinfikovaných
populácií vijačky kukuričnej spórami patogéna N. pyrausta.
8. CONTRIBUTION OF THE WORK FOR PRACTICAL USE AND SCIENCE
Based on obtained data and results of the study, there were developed recommendations for
agricultural praxis and future science development.
Correlation coefficients between the occurrence of O. nubilalis or H. armigera larvae and the
presence of maize pathogens were confirmed only partly and only in favourable years. This is
not in coincidence with many other authors. Complete confirmation or deny of these factors
probably needs long term observation in broader scale on locations with regular secure of
locations in same area for a long time period. Our study was done on many localities, hybrids
or years. So, we support the opinion, that correlation between the occurrence of pests and
infection by pathogens on maize plants is rather week. This change also the meaning of
farmers that pest are responsible for strong pathogen development in maize fields.
Climatic factors and conditions influenced O. nubilalis infestation and there were locations
with regular pest presence over years. For the science it is important to know, that at the same
locality it can be found high population of the pest in any year. So, the influence of short term
weather conditions is relatively week. This fact is important for agricultural praxis. Potential
solution in the case of crop protection can be recommended in right agricultural practices technology, chemical treatment or the use of modified maize hybrids – biotechnology.
Due to study results it was confirmed, that maize hybrid choice does not influence pest
presence and damage. This fact is important for future science development, breeding and
agricultural practice as well. There were many studies, that showed more O. nubilalis resistant
or O. nubilalis toleant hybrids. These was not confirmed in our results. So, we can not
recommend any conventional maize hybrid as a hybrid resistant or tolerant to O. nubilalis. It
means that locations under regular pest presence are recommended for right agricultural
practices, chemical treatment or the use of modified maize hybrids – biotechnology.
Natural enemies of O. nubilalis are still present in Slovakia even their influence to the pest
population under current conditions and agricultural praxis is low. Potencial of increasing
parasitoids presence in O. nubilalis populations is closely connected with agricultural praxis.
It means for example reduction or just targeted chemical treatment, securing natural biotops
with food and shelter sources, eradication of non-honey and nectare weeds around maize
field. Our study showed, that any ecological approach will probably not increase enough the
level of natural enemies of O. nubilalis and in this time there is not real any practical
application of natural enemies in the control of O. nubilalis.
According to our results, Nosema pyrausta is the pathogen which is closely connected with O.
nubilalis and geographical areas from where it is not spreading strongly. This fact is
interesting for the next science development, where the factors for spreading of this pathogen
could be investigated, even the factors of horizontal and vertical transmission are known.
Based on obtained data this pathogen did not provoke huge changes between infected and uninfected populations of O. nubilalis populations from various countries. This can be useful for
stronger knowledge of pathogen epidemiology and potencial correlation between pathogen
influence and pest genetical aspect.
207
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10. APPENDIX
10.1. O. nubilalis population and infestation in Slovakia
Table 1. Number of damages caused by different pests and population density of pest larvae
or adults observed on 100 plants of each hybrid. Locality Farárske (Trnava), Slovakia. Date of
observation: August 25, 2006. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
ON/100 - average number of ON damages per plant.
Error! Not a valid link.
Table 2. Number of damages caused by different pests and population density of pest larvae
or adults observed on 100 plants of each hybrid. Locality Šoporňa, Slovakia. Date of
observation: September 28, 2006. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
ON/100 - average number of ON damages per plant.
Error! Not a valid link.
Table 3. Number of damages caused by different pests and population density of pest larvae
or adults observed on 100 plants of each hybrid. Locality Kalná nad Hronom, Slovakia. Date
of observation: September 30, 2006. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
ON/100 - average number of ON damages per plant.
Error! Not a valid link.
247
Table 4. Number of damages caused by different pests and population density of pest larvae
or adults observed on 100 plants of each hybrid. Locality Veľký Meder, Slovakia. Date of
observation: September 6, 2006. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
ON/100 - average number of ON damages per plant.
Error! Not a valid link.
Table 5. Number of damages caused by different pests and population density of pest larvae
or adults observed on 100 plants of each hybrid. Locality Jánošíkovo (Tvrdošovce), Slovakia.
Date of observation: September 11, 2006. ON – O. nubilalis, DVV – Diabrotica virgifera
virgifera, ON/100 - average number of ON damages per plant.
Error! Not a valid link.
Table 6. Number of damages caused by different pests and population density of pest larvae
or adults observed on 100 plants of each hybrid. Locality Borovce, Slovakia. Date of
observation: October 12, 2006. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
ON/100 - average number of ON damages per plant.
Error! Not a valid link.
Table 7. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Borovce, Slovakia. Date of
observation: September 14, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
DKC5143
248
Damage caused by
ON larvae
above
ear
below ear
1
0
4
ON
sum
sum/50
5
0.1
Broken stalks
caused by
Fusarium
ON
spp.
4
0
Helicoverpa
zea damage
0
DVV
adults
0
Damage caused by
Ustilago Helminthosp.
spp.
spp.
0
0
Rust
0
DKC4442YG
0
0
0
0
0
0
0
0
0
0
0
0
DKC4964
5
5
0
10
0.2
7
0
1
0
0
0
0
DKC4626
0
8
2
10
0.2
1
0
0
0
0
0
0
DKC5542
0
8
0
8
0.16
1
0
0
0
0
0
0
ND4903
1
2
3
6
0.12
2
0
0
0
0
0
0
DKC5143
0
3
2
5
0.1
0
0
1
0
0
0
0
DK471
1
8
1
10
0.2
1
0
0
0
0
0
0
ED5206
1
2
0
3
0.06
2
0
1
0
0
0
0
NC5209
0
7
1
8
0.16
0
0
2
2
0
0
0
EE4809
0
2
5
7
0.14
1
0
1
0
0
0
0
DK527
0
4
3
7
0.14
0
0
2
2
0
0
0
DKC5143
1
5
0
6
0.12
3
0
0
2
0
0
0
Average number per plant
0.13
Table 8. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Soblahov, Slovakia. Date of
observation: October 11, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust
– Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by
ON larvae
above
ear
below ear
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
0
10
2
12
0.24
4
0
0
0
2
0
0
DK471
2
13
0
15
0.3
9
0
0
1
2
0
0
PR37M43
2
11
4
17
0.34
7
0
1
0
1
0
0
DKC4964
1
5
1
7
0.14
4
0
1
0
1
0
0
NC4702
0
4
1
5
0.1
2
0
0
0
3
0
0
EE4401
0
10
1
11
0.22
4
0
0
0
3
0
0
PR37D25
0
4
2
6
0.12
2
0
0
0
1
0
0
DKC4626
0
7
0
7
0.14
6
0
1
0
0
0
0
DKC3511
2
7
2
11
0.22
7
0
0
0
0
0
0
ED4501
0
11
0
11
0.22
10
0
1
0
3
0
0
DK440
1
5
0
6
0.12
1
0
1
0
2
0
0
PR38A24
1
6
1
8
0.16
5
0
0
0
3
0
0
NK Thermo
3
8
5
16
0.32
5
0
0
0
1
0
0
EC3903
0
4
0
4
0.08
3
0
1
0
1
0
0
DKC4372
0
8
4
12
0.24
4
0
1
0
2
0
0
DKC 4860
0
7
0
7
0.14
3
0
4
0
2
0
0
3
0
3
0.06
2
0
1
0
0
0
0
DKC3511
0
Average number per plant
249
sum/50
Helicoverpa
DVV
adults
Hybrid
DKC 3511
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
0.19
Rust
Table 9. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Perín, Slovakia. Date of observation:
September 22, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust –
Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by
ON larvae
above
ear
below ear
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DKC 3511
0
0
2
2
0.04
0
0
6
0
0
0
0
DKC4626
3
2
2
7
0.14
0
0
16
0
0
0
0
ED4501
0
0
5
5
0.1
0
0
6
0
0
0
0
EE4605
1
8
4
13
0.26
0
0
8
0
0
0
0
NC4702
0
3
4
7
0.14
0
0
4
0
0
0
0
EE4401
1
0
0
1
0.02
0
0
0
0
0
0
0
PR38A24
3
1
1
5
0.1
0
0
6
0
0
0
0
EC3903
0
1
0
1
0.02
0
0
7
0
0
0
0
DKC3511
1
0
2
3
0.06
0
0
3
0
0
0
0
DK440
0
1
1
2
0.04
0
0
3
0
0
0
0
NK Thermo
1
1
1
3
0.06
0
0
2
0
0
0
0
PR37D25
1
1
0
2
0.04
0
0
1
0
0
0
0
DKC4964
4
0
1
5
0.1
0
0
4
0
0
0
0
PR37M43
0
1
2
3
0.06
0
0
1
0
0
0
0
DK471
0
2
1
3
0.06
0
0
2
0
0
0
0
DKC4860
0
3
0
3
0.06
0
0
0
0
0
0
0
DKC4372
2
0
2
4
0.08
0
0
2
0
0
0
0
0
3
3
0.06
0
0
3
0
0
0
0
DKC 3511
0
Average number per plant
250
sum/50
Helicoverpa
DVV
adults
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
0.08
Rust
Table 10. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Macov, Slovakia. Date of
observation: September 16, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by
ON larvae
above
ear
below ear
sum/50
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
0
0
0
0
0
0
0
4
0
0
0
0
ED4501
1
0
0
1
0.02
1
0
4
0
0
0
0
NK Thermo
0
0
2
2
0.04
2
0
5
0
0
0
0
EC3903
1
1
2
4
0.08
0
0
1
0
0
0
0
PR37M43
0
0
0
0
0
0
0
0
0
0
0
0
EE4401
0
1
1
2
0.04
0
0
4
0
0
0
0
DKC3511
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
2
0
DK440
0
0
0
0
NC4702
0
0
0
0
0
0
0
3
0
0
0
0
Hybrid
DKC 3511
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
Rust
PR37D25
1
2
2
5
0.1
1
0
0
0
0
0
0
DKC4964
0
0
0
0
0
0
0
1
0
0
0
0
PR38A24
0
1
0
1
0.02
0
0
3
0
0
0
0
DKC4626
0
1
2
3
0.06
1
0
1
0
0
0
0
DK471
0
2
0
2
0.04
0
0
4
0
0
0
0
DKC4372
0
3
0
3
0.06
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
DKC4860
DKC3511
0
0
Average number per plant
251
0
0
0
0
0
0
3
1
1
2
0.04
0
0
1
0.03
Table 11. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Nacina Ves, Slovakia. Date of
observation: September 22, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by
ON larvae
above
ear
below ear
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
0
5
1
6
0.12
0
0
3
2
0
0
0
ED4501
2
4
2
8
0.16
1
0
2
2
1
0
0
EE4401
0
7
3
10
0.2
0
0
1
2
2
0
0
NK Thermo
0
2
0
2
0.04
0
0
2
6
0
0
0
PR37M43
1
3
0
4
0.08
1
0
3
3
4
0
0
NC4702
2
5
1
8
0.16
1
0
1
7
1
0
0
DKC4626
0
3
2
5
0.1
0
0
2
2
0
0
0
DK471
1
5
3
9
0.18
0
0
0
1
2
0
0
DKC3511
1
3
2
6
0.12
1
0
0
1
1
0
0
EC3903
2
4
2
8
0.16
0
0
0
3
0
0
0
PR38A24
1
6
1
8
0.16
1
0
4
0
0
0
0
DKC4964
1
2
0
3
0.06
0
0
0
3
0
0
0
DK440
1
1
0
2
0.04
1
0
3
0
0
0
0
PR37D25
0
2
1
3
0.06
0
0
1
2
0
0
0
DKC442YG
0
0
0
0
0
0
0
0
0
1
0
0
DKC4860
0
3
0
3
0.06
0
0
1
4
1
0
0
DKC4372
0
2
0
2
0.04
0
0
1
1
0
0
0
2
1
6
0.12
3
0
0
2
0
0
0
DKC3511
3
Average number per plant
252
sum/50
Helicoverpa
DVV
adults
Hybrid
DKC 3511
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
0.10
Rust
Table 12. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Trhovište, Slovakia. Date of
observation: September 23, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by
ON larvae
above
ear
below ear
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
1
3
7
11
0.22
1
0
3
0
0
0
0
NC4702
1
0
0
1
0.02
1
0
2
0
0
0
0
DKC4626
0
3
1
4
0.08
1
0
3
0
0
0
0
DK440
0
1
0
1
0.02
0
0
1
0
0
0
0
PR38A24
0
0
0
0
0
0
0
2
0
0
0
0
PR37D25
0
3
1
4
0.08
0
0
1
0
0
0
0
DKC4964
1
1
0
2
0.04
1
0
1
0
1
0
0
DKC3511
0
5
1
6
0.12
0
0
0
0
0
0
0
EC3903
0
4
2
6
0.12
1
0
1
0
0
0
0
ED4501
0
5
0
5
0.1
4
0
0
0
0
0
0
EE4401
1
5
1
7
0.14
1
0
0
0
0
0
0
NK Thermo
3
3
1
7
0.14
4
0
2
0
0
0
0
PR37M43
0
5
1
6
0.12
2
0
0
0
0
0
0
DK471
1
4
0
5
0.1
2
0
2
0
0
0
0
DKC4372
2
0
1
3
0.06
2
0
0
0
0
0
0
DKC442YG
0
0
0
0
0
0
0
0
0
0
0
0
DKC4860
1
3
1
5
0.1
1
0
3
0
0
0
0
7
3
11
0.22
2
0
1
0
1
0
0
DKC3511
1
Average number per plant
253
sum/50
Helicoverpa
DVV
adults
Hybrid
DKC 3511
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
0.09
Rust
Table 13. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Choňkovce, Slovakia. Date of
observation: September 24, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by
ON larvae
above
ear
below ear
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DKC 3511
PR37M43
0
1
10
11
0.22
0
0
18
0
0
0
0
0
9
9
18
0.36
0
0
14
0
2
0
0
EE4605
0
1
6
7
0.14
0
0
20
2
2
0
0
DKC4964
0
0
5
5
0.1
0
0
16
0
0
0
0
EC3903
0
2
0
2
5
7
5
0.1
0
0
0
0.22
0
0
0
1
0
0
11
14
10
0
DK440
0
0
NK Thermo
0
0
3
3
0.06
0
0
9
0
2
0
0
PR37D25
1
3
4
8
0.16
0
0
9
0
0
0
0
DKC3511
0
2
1
3
0.06
0
0
18
0
3
0
0
DK471
0
3
7
10
0.2
0
0
10
0
0
0
0
ED4501
0
2
8
10
0.2
0
0
15
0
3
0
0
NC4702
0
3
4
7
0.14
0
0
2
0
0
0
0
PR38A24
0
0
8
8
0.16
0
0
9
0
0
0
0
EE4401
1
0
5
6
0.12
0
0
10
0
0
0
0
DKC4626
0
1
6
7
0.14
0
0
8
0
0
0
0
DKC4372
0
2
4
6
0.12
0
0
11
0
0
0
0
DKC4860
0
0
6
6
0.12
0
0
9
0
0
0
0
DKC442YG
0
0
0
0
0
0
0
0
0
0
0
0
0
4
5
0.1
0
0
10
0
0
0
0
DKC3511
1
Average number per plant
254
sum/50
Helicoverpa
DVV
adults
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
0.14
Rust
Table 14. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Parchovany, Slovakia. Date of
observation: September 24, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by
ON larvae
above
ear
below ear
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
1
1
0
2
0.04
1
0
4
0
0
0
0
DKC4964
1
1
0
2
0.04
2
0
2
0
2
0
0
NC4702
0
0
2
2
0.04
0
0
2
0
3
0
0
NK Thermo
0
2
1
3
0.06
0
0
1
0
2
0
0
PR37M43
0
7
1
8
0.16
1
0
2
0
2
0
0
ED4501
0
2
0
2
0.04
0
0
0
0
0
0
0
PR38A24
0
2
1
3
0.06
0
0
8
0
1
0
0
DKC3511
0
3
2
5
0.1
1
0
1
0
1
0
0
EE4605
1
3
0
4
0.08
0
0
1
0
0
0
0
EE4401
0
1
1
2
0.04
0
0
4
0
2
0
0
DK471
0
0
1
1
0.02
0
0
1
0
1
0
0
PR37D25
0
3
0
3
0.06
1
0
3
0
0
0
0
DK440
0
1
0
1
0.02
0
0
1
0
1
0
0
EC3903
0
3
1
4
0.08
1
0
0
0
0
0
0
DKC4626
0
0
2
2
0.04
0
0
2
0
0
0
0
DKC4860
0
3
0
3
0.06
0
0
0
0
1
0
0
DKC4372
0
0
1
1
0.02
0
0
3
0
0
0
0
DKC442YG
0
0
0
0
0
0
0
0
0
0
0
0
1
1
2
0.04
0
0
1
0
0
0
0
DKC3511
0
Average number per plant
255
sum/50
Helicoverpa
DVV
adults
Hybrid
DKC 3511
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
0.05
Rust
Table 15. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Čakajovce, Slovakia. Date of
observation: September 16, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
DKC5143
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
0
0
3
3
0.06
0
0
5
0
0
0
0
DKC5542
2
1
4
7
0.14
0
0
7
0
0
0
0
NC5209
0
1
1
2
0.04
0
0
1
1
0
0
0
PR36K67
1
2
3
6
0.12
0
0
5
0
1
0
0
NK Thermo
0
3
0
3
0.06
0
0
2
0
0
0
0
PR37F73
1
1
1
3
0.06
0
0
2
0
0
0
0
NK Cisco
0
5
0
5
0.1
0
0
1
0
0
0
0
EE4809
1
0
1
2
0.04
0
0
2
0
0
0
0
DKC5143
0
2
2
4
0.08
0
0
5
0
0
0
0
ED5206
0
0
1
1
0.02
0
0
1
0
0
0
0
DKC4626
0
2
0
2
0.04
0
0
2
0
2
0
0
ND4903
0
1
2
3
0.06
0
0
0
0
2
0
0
DKC4964
3
0
0
3
0.06
0
0
3
0
1
0
0
DK527
0
2
0
2
0.04
0
0
1
1
2
0
0
DK471
0
4
2
6
0.12
0
0
3
0
5
0
0
3
6
9
0.18
0
0
6
4
3
0
0
DKC5143
0
Average number per plant
0.08
Table 16. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Palárikovo, Slovakia. Date of
observation: September 17, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
DKC5143
Damage caused by
ON larvae
above
ear
below ear
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
ON
sum
sum/50
zea damage
DVV
adults
0.14
0
0
1
0
0
0
0
Rust
2
2
3
7
NC5209
1
2
2
5
0.1
0
0
1
0
0
0
0
DKC5542
1
1
2
4
0.08
0
0
2
0
0
0
0
NK Thermo
2
3
0
5
0.1
0
0
0
0
1
0
0
NK Cisco
2
3
2
7
0.14
0
0
1
0
0
0
0
256
ND4903
0
3
2
5
0.1
0
0
0
0
0
0
0
DK527
1
0
1
2
0.04
0
0
1
0
2
0
0
EE4809
0
2
1
3
0.06
0
0
0
0
0
0
0
DKC5143
0
0
1
1
0.02
0
0
1
0
0
0
0
PR37F73
1
2
2
5
0.1
0
0
0
0
0
0
0
DKC4964
1
1
3
5
0.1
0
0
1
0
0
0
0
PR36K67
0
0
1
1
0.02
0
0
0
0
1
0
0
DK471
3
0
2
5
0.1
0
0
0
0
2
0
0
ED5206
1
1
1
3
0.06
0
0
2
0
0
0
0
DKC4626
1
0
2
3
0.06
0
0
0
0
0
0
0
1
1
3
0.06
0
0
1
0
0
0
0
DKC5143
1
Average number per plant
0.08
Table 17. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Šoporňa, Slovakia. Date of
observation: September 17, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by
ON larvae
above
ear
below ear
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
0
5
0
5
0.1
0
0
0
0
0
0
0
NK Cisco
0
2
0
2
0.04
0
0
0
0
1
0
0
DKC4626
1
4
1
6
0.12
0
0
0
0
3
0
0
PR36K67
0
7
0
7
0.14
0
0
0
0
2
0
0
ND4903
2
10
0
12
0.24
0
0
0
0
3
0
0
DK471
0
3
1
4
0.08
0
0
0
0
3
0
0
DKC4964
0
5
0
5
0.1
0
0
2
0
2
0
0
EE4809
0
1
1
2
0.04
0
0
0
0
1
0
0
DKC5143
2
2
2
6
0.12
0
0
1
0
1
0
0
NK Thermo
3
5
1
9
0.18
0
0
0
0
4
0
0
NC5209
0
0
2
2
0.04
0
0
3
0
1
0
0
DK527
1
4
1
6
0.12
0
0
3
0
0
0
0
PR37F73
0
2
2
4
0.08
0
0
0
0
0
0
0
DKC5542
2
1
2
5
0.1
0
0
1
0
3
0
0
ED5206
0
2
0
2
0.04
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
DKC5143
0
Average number per plant
sum/50
Helicoverpa
DVV
adults
Hybrid
DKC5143
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
Rust
0.10
Table 18. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Veľký Meder, Slovakia. Date of
observation: September 29, 2007. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
DKC5143
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
0
11
0
11
0.22
0
0
0
0
0
0
0
NK Cisco
0
4
3
7
0.14
0
0
2
0
0
0
0
DK527
6
4
3
13
0.26
0
0
3
0
2
0
0
ND4903
3
5
5
13
0.26
0
0
2
0
1
0
0
PR36K67
0
9
2
11
0.22
0
0
1
0
0
0
0
257
PR37F73
2
1
1
4
0.08
0
0
2
0
1
0
0
NK Thermo
0
3
4
7
0.14
0
0
3
0
0
0
0
ED5206
1
2
2
5
0.1
0
0
2
0
0
0
0
DKC5143
2
5
4
11
0.22
0
0
2
0
2
0
0
EE4809
0
1
1
2
0.04
0
0
1
0
0
0
0
NC5209
3
4
3
10
0.2
0
0
2
0
2
0
0
DK471
1
3
3
7
0.14
0
0
1
0
1
0
0
DKC5542
0
2
6
8
0.16
0
0
0
0
1
0
0
DKC4964
0
1
2
3
0.06
0
0
1
0
0
0
0
DKC4626
0
4
2
6
0.12
0
0
1
0
0
0
0
1
1
5
0.1
0
0
1
0
0
0
0
DKC5143
3
Average number per plant
0.15
Table 19. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Bajč, Slovakia. Date of observation:
September 22, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust –
Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC5143
4
5
6
15
0.30
1
0
3
0
0
0
EF4705
0
8
4
12
0.24
4
0
2
1
0
0
0
NE4711
3
8
6
17
0.34
1
0
0
1
0
0
0
DKC 4983
0
3
6
9
0.18
1
0
1
0
0
0
0
EE4809
2
5
12
19
0.38
2
0
0
0
1
0
0
DKC5170
0
4
11
15
0.30
1
0
1
2
0
0
0
DKC4964
0
3
4
7
0.14
0
0
1
0
0
0
0
DKC5143
DKC
5018YG
0
3
9
12
0.24
1
0
1
1
0
0
0
0
0
0
0
0.00
0
0
0
3
0
0
0
DKC5276
0
4
5
9
0.18
1
0
0
1
0
0
0
MEB 483BT
0
0
0
0
0.00
0
0
0
0
0
0
0
DKC4626
0
7
6
13
0.26
1
0
1
2
0
0
0
PR 37F73
3
5
5
13
0.26
4
0
0
0
0
PR 36D79
0
6
2
8
0.16
0
0
2
3
0
0
0
NK Cisco
3
13
4
20
0.40
2
0
0
0
0
0
0
ED5206EZA2
0
0
0
0
0.00
0
0
0
0
0
0
0
DK471
3
3
6
12
0.24
2
0
0
0
0
0
0
DKC5143
0
5
4
9
0.18
1
0
0
0
0
0
0
Average number per plant
258
0.21
Table 20. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Veľký Meder, Slovakia. Date of
observation: October 22, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust
– Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC5143
11
0
11
22
0.44
10
0
0
0
0
0
0
PR 37F73
2
19
4
25
0.50
2
0
0
0
0
0
0
EF4705
6
5
8
19
0.38
8
0
0
0
0
0
0
DKC5170
0
16
13
29
0.58
3
0
0
0
0
0
0
PR 36D79
6
2
3
11
0.22
14
0
0
0
0
0
0
NE4711
0
13
5
18
0.36
7
0
0
0
0
0
0
NK Cisco
4
7
8
19
0.38
1
0
0
0
0
0
0
DKC5143
1
8
6
15
0.30
4
0
0
0
0
0
0
EE4809
2
9
5
16
0.32
1
0
0
0
0
0
0
DKC 4983
0
10
10
20
0.40
2
0
0
0
0
0
0
DKC5276
4
4
16
24
0.48
4
0
0
0
0
0
0
DKC4964
2
3
8
13
0.26
3
0
0
0
0
0
0
DKC5143
4
13
8
25
0.50
3
0
0
0
0
0
0
Average number per plant
0.39
Table 21. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Sokolce, Slovakia. Date of
observation: October 22, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust
– Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC5143
3
9
9
21
0.42
3
0
0
0
0
0
0
DKC5170
1
20
5
26
0.52
2
0
0
0
0
0
0
NK Cisco
1
10
12
23
0.46
2
0
0
0
0
0
0
EF4705
0
18
0
18
0.36
2
0
0
0
0
0
0
NE4711
4
8
9
21
0.42
4
0
0
0
0
0
0
259
PR 37F73
0
9
2
11
0.22
2
0
0
0
0
0
0
EE4809
4
5
2
11
0.22
10
0
0
0
1
0
0
DKC5143
0
10
2
12
0.24
0
0
0
0
0
0
0
DKC4626
2
9
12
23
0.46
2
0
0
0
0
0
0
DKC4964
0
14
2
16
0.32
2
0
0
0
0
0
0
DKC 4983
9
3
5
17
0.34
5
0
1
1
0
0
0
DK471
1
19
3
23
0.46
1
0
0
0
0
0
0
PR 36D79
3
12
7
22
0.44
4
0
0
2
1
0
0
DKC5276
0
17
1
18
0.36
1
0
0
0
0
0
0
DKC5143
0
17
0
17
0.34
2
0
0
0
0
0
0
Average number per plant
0.37
Table 22. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Tešedíkovo, Slovakia. Date of
observation: September 16, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC5143
1
14
9
24
0.48
2
0
0
2
4
0
0
PR 36D79
3
11
2
16
0.32
0
0
0
0
0
0
0
DKC5170
2
8
7
17
0.34
3
0
0
0
3
0
0
NE4711
0
8
4
12
0.24
2
0
0
1
0
0
0
EF4705
1
9
6
16
0.32
1
0
0
0
8
0
0
EE4809
0
9
2
11
0.22
0
0
0
0
0
0
0
NK Cisco
4
3
4
11
0.22
5
0
3
0
0
0
0
DKC5143
0
6
6
12
0.24
2
0
0
1
1
0
0
DKC4964
3
5
7
15
0.30
3
0
0
0
3
0
0
DKC5276
0
12
1
13
0.26
1
0
0
0
2
0
0
DK471
0
0
0
0
0.00
0
0
0
0
0
0
0
DKC 4983
0
16
1
17
0.34
1
0
0
0
2
0
0
PR 37F73
2
4
4
10
0.20
4
0
0
0
4
0
0
DKC4626
0
10
4
14
0.28
3
0
0
0
2
0
0
DKC5143
1
4
0
5
0.10
0
0
0
0
0
0
0
Average number per plant
260
0.26
Table 23. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Kameničná, Slovakia. Date of
observation: September 23, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC5143
0
1
4
5
0.10
0
0
1
0
0
0
0
PR 37F73
1
0
8
9
0.18
1
0
1
1
0
0
0
NE4711
3
4
4
11
0.22
3
0
1
0
0
0
0
DKC4626
2
3
8
13
0.26
1
0
0
0
0
0
0
EE4809
1
3
5
9
0.18
0
0
0
0
0
0
0
EF4705
0
6
8
14
0.28
0
0
0
6
0
0
0
DKC5170
3
4
8
15
0.30
0
0
0
3
0
0
0
DKC5143
2
4
4
10
0.20
1
0
0
0
0
0
0
DKC5276
0
8
4
12
0.24
0
0
0
0
0
0
0
DK471
0
4
6
10
0.20
0
0
0
0
0
0
0
DKC4964
1
3
9
13
0.26
0
0
0
3
0
0
0
NK Cisco
0
5
12
17
0.34
0
0
0
1
0
0
0
DKC 4983
1
4
8
13
0.26
0
0
0
0
0
0
0
PR 36D79
1
4
19
24
0.48
1
0
0
0
0
0
0
DKC5143
1
5
8
14
0.28
1
0
0
0
0
0
0
Average number per plant
261
0.25
Table 24. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Macov, Slovakia. Date of
observation: September 14, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC5143
1
1
8
10
0.20
2
0
0
0
0
0
0
NE4711
1
6
6
13
0.26
2
0
0
0
1
0
0
DKC5276
1
1
6
8
0.16
1
0
0
0
0
0
0
EE4809
0
6
1
7
0.14
1
0
0
0
0
0
0
NK Cisco
3
4
7
0.14
4
0
0
0
0
0
0
PR 37F73
0
4
7
11
0.22
0
0
0
0
0
0
0
EF4705
4
4
7
15
0.30
4
0
0
0
0
0
0
DKC5143
1
8
3
12
0.24
1
0
0
0
0
0
0
DK471
1
2
7
10
0.20
0
0
0
0
1
0
0
DKC5170
0
3
1
4
0.08
1
0
0
0
0
0
0
PR 36D79
1
1
3
5
0.10
1
0
0
0
0
0
0
DKC4964
0
4
1
5
0.10
1
0
0
0
0
0
0
DKC4626
4
2
3
9
0.18
2
0
0
0
1
0
0
DKC 4983
0
4
2
6
0.12
0
0
0
0
2
0
0
DKC5143
0
5
0
5
0.10
1
0
0
0
0
0
0
Average number per plant
262
0.17
Table 25. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Klasov, Slovakia. Date of
observation: September 16, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
1
12
0
13
0.26
4
0
0
2
0
0
0
TPA422-H
0
0
0
0
0.00
0
0
0
0
0
0
0
DKC4964
0
2
0
2
0.04
0
0
1
0
0
0
0
DKC4490
0
7
0
7
0.14
0
0
0
3
1
0
0
DKC3511
5
0
5
10
0.20
6
0
0
0
0
0
0
PR 37D25
0
15
0
15
0.30
0
0
0
0
3
0
0
DKC4626
0
12
0
12
0.24
0
0
0
0
0
0
0
MEB483BT
0
0
0
0
0.00
0
0
0
0
0
0
0
NK Termo
6
9
3
18
0.36
6
0
0
0
0
0
0
DKC4372
0
24
0
24
0.48
3
0
0
0
0
0
0
DKC4860
0
15
0
15
0.30
1
0
0
0
0
0
0
ED5206EZA3
0
0
0
0
0.00
0
0
0
0
0
0
0
DK440
2
15
3
20
0.40
6
0
0
0
0
0
0
DKC4442YG
0
0
0
0
0.00
0
0
0
0
0
0
0
DKC3511
0
16
0
16
0.32
8
0
0
0
1
0
0
Average number per plant
263
0.20
Table 26. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Borovce, Slovakia. Date of
observation: September 11, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
1
9
3
13
0.26
1
0
0
0
0
0
0
DKC4490
3
7
8
18
0.36
0
0
0
9
1
0
0
DK440
2
5
2
9
0.18
3
0
0
3
0
0
0
DKC4442YG
0
0
0
0
0.00
0
0
0
1
0
2
0
DKC3511
3
13
4
20
0.40
6
0
0
9
0
0
0
DKC4964
2
2
6
10
0.20
6
0
1
7
0
1
0
DKC4626
3
9
5
17
0.34
3
0
0
9
0
0
0
MEB483BT
0
0
0
0
0.00
0
0
0
5
0
0
0
PR 37D25
4
10
2
16
0.32
7
0
0
4
0
0
0
DKC4860
0
7
1
8
0.16
4
0
0
6
0
1
0
DKC4372
5
11
5
21
0.42
0
0
0
4
0
0
0
NK Termo
1
11
0
12
0.24
8
0
0
9
0
0
0
TPA422-H
0
0
0
0
0.00
0
0
0
0
0
0
0
DKC3511
0
9
3
12
0.24
6
0
0
0
0
0
0
Average number per plant
264
0.22
Table 27. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Nitra, Slovakia. Date of observation:
September 29, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust –
Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by
ON larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
0
9
1
10
0.20
1
0
1
1
0
0
0
DKC4372
0
8
0
8
0.16
0
0
0
0
0
0
0
MEB483BT
0
0
0
0
0.00
0
0
1
5
0
0
0
DKC4626
0
15
0
15
0.30
0
0
0
0
0
0
0
DKC3511
4
2
6
12
0.24
6
0
0
0
0
0
0
TPA422-H
0
0
0
0
0.00
0
0
0
0
0
0
0
DKC4860
4
8
2
14
0.28
4
0
0
3
0
0
0
DKC4490
2
16
2
20
0.40
1
0
0
0
0
0
0
NK Termo
1
7
1
9
0.18
4
0
0
0
0
0
0
ED5206EZA3
0
0
0
0
0.00
0
0
0
0
0
0
0
DKC4964
1
5
3
9
0.18
1
0
0
1
0
0
0
DKC4442YG
0
0
0
0
0.00
0
0
0
0
0
0
0
DK440
0
16
1
17
0.34
2
0
0
0
0
0
0
PR 37D25
2
12
1
15
0.30
0
0
0
0
0
0
0
DKC3511
3
7
2
12
0.24
7
0
0
0
0
0
0
Average number per plant
0.19
Table 28. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Bardoňovo, Slovakia. Date of
observation: September 22, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
DKC3511
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
12
5
8
25
0.50
DKC4626
0
28
3
31
DKC4372
11
11
4
26
NK Termo
0
25
1
DKC3511
10
13
DK440
0
18
265
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
16
0
0
0
0
0
0
0.62
0
0
1
0
0
0
0
0.52
10
0
0
0
0
0
0
26
0.52
8
0
0
1
0
0
0
3
26
0.52
15
0
0
0
0
0
0
3
21
0.42
2
0
0
0
0
0
0
DKC4860
12
16
3
31
0.62
11
0
0
0
0
0
0
DKC4490
0
31
0
31
0.62
6
0
0
0
0
0
0
PR 37D25
13
15
1
29
0.58
7
0
0
0
0
0
0
DKC4964
4
22
1
27
0.54
1
0
0
0
0
0
0
DKC3511
5
17
1
23
0.46
5
0
0
0
0
0
0
Average number per plant
0.54
Table 29. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Kalná nad Hronom, Slovakia. Date of
observation: September 22, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
sum/50
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
DKC3511
0
12
0
12
0.24
5
0
0
0
0
0
0
DKC4005
0
25
1
26
0.52
4
0
0
0
0
0
0
EE4401
0
17
1
18
0.36
2
0
0
0
0
0
0
PR 39D81
0
16
0
16
0.32
2
0
0
0
0
0
0
DK315
3
8
1
12
0.24
4
0
0
0
0
0
0
DKC3511
0
14
4
18
0.36
0
0
0
0
2
0
0
PR 38 B12
4
6
4
14
0.28
10
0
0
0
0
0
0
EE3905
0
31
0
31
0.62
0
0
0
0
0
0
0
NK Altius
4
14
1
19
0.38
4
0
0
0
0
0
0
DKC3759
0
20
1
21
0.42
0
0
0
0
1
0
0
DK391
0
28
0
28
0.56
8
0
0
0
0
0
0
DKC3511
0
26
3
29
0.58
0
0
0
0
0
0
0
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
Average number per plant
Rust
0.41
Table 30. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Čakajovce, Slovakia. Date of
observation: September 24, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
4
14
1
19
0.38
4
0
0
0
0
0
0
EE3905
1
28
0
29
0.58
3
0
0
0
0
0
0
EE4401
4
11
0
15
0.30
5
0
0
7
0
0
0
DK315
1
5
1
7
0.14
2
0
0
0
1
0
0
DK391
3
2
2
7
0.14
4
0
0
0
0
0
0
DKC3511
1
11
0
12
0.24
2
0
0
0
0
0
0
PR 39D81
7
2
2
11
0.22
10
0
0
2
1
0
0
PR 38 B12
0
10
0
10
0.20
3
0
0
0
1
0
0
NK Altius
4
10
0
14
0.28
5
0
0
0
0
0
0
266
DKC3759
0
15
0
15
0.30
0
0
0
0
0
0
0
DKC4005
1
13
0
14
0.28
0
0
0
0
0
0
0
DKC3511
0
20
0
20
0.40
0
0
0
0
0
0
0
Average number per plant
0.29
Table 31. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Čachtice, Slovakia. Date of
observation: October 2, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust
– Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
0
7
0
7
0.14
4
0
0
0
0
0
0
DK391
2
0
2
4
0.08
6
0
0
0
0
0
0
EE3905
0
5
1
6
0.12
10
0
0
0
1
0
0
PR 38 B12
0
3
0
3
0.06
1
0
0
0
0
0
0
DKC3759
0
0
3
3
0.06
12
0
0
0
0
0
0
DKC3511
0
2
0
2
0.04
0
0
0
0
0
0
0
DKC4005
0
5
0
5
0.10
6
0
0
0
1
0
0
NK Altius
0
3
1
4
0.08
2
0
0
0
0
0
0
EE4401
0
5
1
6
0.12
1
0
0
0
2
0
0
PR 39D81
1
0
1
2
0.04
4
0
0
0
0
0
0
DK315
0
2
0
2
0.04
1
0
0
0
0
0
0
DKC3511
0
7
0
7
0.14
4
0
0
0
0
0
0
Average number per plant
0.09
Table 32. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Budmerice, Slovakia. Date of
observation: September 2, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
0
8
3
11
0.22
3
0
0
0
0
0
0
DKC3759
0
12
0
12
0.24
3
0
0
0
0
0
0
DK315
0
14
0
14
0.28
3
0
0
0
0
0
0
DKC4005
0
13
0
13
0.26
2
0
0
0
0
0
0
EE3905
0
15
0
15
0.30
4
0
0
0
0
0
0
DKC3511
0
7
1
8
0.16
0
0
1
0
0
0
0
EE4401
0
18
1
19
0.38
0
0
0
0
0
0
0
PR 39D81
0
16
1
17
0.34
5
0
0
0
0
0
0
DK391
0
17
1
18
0.36
3
0
0
0
0
0
0
267
NK Altius
0
17
0
17
0.34
3
0
0
0
0
0
0
PR 38 B12
0
16
0
16
0.32
1
0
0
0
0
0
0
DKC3511
0
17
1
18
0.36
2
0
0
0
0
0
0
Average number per plant
0.30
Table 33. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Šalgovce, Slovakia. Date of
observation: September 3, 2008. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
3
13
0
16
0.32
9
0
0
0
0
0
0
DK315
0
15
1
16
0.32
3
0
0
0
0
0
0
DKC4005
3
2
2
7
0.14
12
0
0
0
0
0
0
EE4401
0
16
3
19
0.38
5
0
0
0
0
0
0
PR 39D81
4
10
1
15
0.30
6
0
0
0
0
0
0
DKC3511
0
16
3
19
0.38
1
0
0
0
0
0
0
EE3905
3
13
0
16
0.32
5
0
0
0
0
0
0
DKC3759
0
13
0
13
0.26
2
0
0
0
0
0
0
PR 38 B12
0
7
0
7
0.14
7
0
0
0
0
0
0
DK391
0
13
1
14
0.28
5
0
0
0
0
0
0
NK Altius
3
10
0
13
0.26
13
0
0
0
0
0
0
DKC3511
4
1
0
5
0.10
7
0
0
0
0
0
0
Average number per plant
0.27
Table 34. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Kalná nad Hronom, Slovakia. Date of
observation: September 21, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
2
11
2
15
0.3
1
0
1
0
0
0
0
NF3715
1
7
0
8
0.16
0
0
0
0
1
0
0
EE3802
1
6
1
8
0.16
1
0
1
0
1
0
0
PR39D81
0
11
0
11
0.22
0
0
0
0
1
0
0
DKC3511
3
8
2
13
0.26
4
0
0
0
0
0
0
Altius
0
8
0
8
0.16
0
0
0
0
0
0
0
DK391
2
3
2
7
0.14
2
0
0
0
0
0
0
NF3905
0
0
0
0
0
0
0
0
0
0
0
0
PR38A79
0
14
0
14
0.28
0
0
1
0
0
0
0
268
NF4217
0
2
4
6
0.12
1
0
0
0
0
0
0
DKC3511
0
7
3
10
0.2
1
0
0
0
0
0
0
Average number per plant
0.18
Table 35. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Čakajovce, Slovakia. Date of
observation: September 17, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
2
4
3
9
0.18
3
0
0
0
0
0
0
PR38A79
1
3
0
4
0.08
0
0
0
0
2
0
0
NF3715
5
9
2
16
0.32
8
0
0
0
0
0
0
DK315
EE3802
(DKC 4082)
0
6
2
8
0.16
0
0
0
0
0
0
0
2
2
0
4
0.08
2
0
0
0
0
0
0
DKC3511
0
7
0
7
0.14
1
0
0
0
0
0
0
DK391
1
7
3
11
0.22
3
0
0
0
0
0
0
PR39D81
0
8
0
8
0.16
3
0
0
0
1
0
0
NKALTIUS
3
8
0
11
0.22
4
0
0
0
0
0
0
NF4217
0
2
2
4
0.08
0
0
0
0
0
0
0
DKC3511
0
4
2
6
0.12
1
0
0
0
0
0
0
Average number per plant
0.16
Table 36. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Čachtice, Slovakia. Date of
observation: September 28, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
1
39
0
40
0.8
2
0
0
0
2
0
0
PR38A79
0
35
0
35
0.7
1
0
0
0
0
0
0
DK391
0
39
0
39
0.78
1
0
0
0
2
0
0
NF3715
0
41
0
41
0.82
3
0
0
0
0
0
0
DK315
0
39
0
39
0.78
3
0
0
0
0
0
0
DKC3511
EE3802
(DKC 4082)
0
35
0
35
0.7
1
0
0
0
0
0
0
0
38
0
38
0.76
0
0
0
0
0
0
0
PR39D81
0
35
0
35
0.7
3
0
0
0
1
0
0
NF4217
0
38
0
38
0.76
3
0
0
0
0
0
0
NKALTIUS
0
35
0
35
0.7
0
0
0
0
0
0
0
269
DKC3511
0
35
0
35
Average number per plant
0.7
0
0
0
0
1
0
0
0.75
Table 37. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Šalgovce, Slovakia. Date of
observation: September 26, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
DKC3511
1
15
0
16
0.32
3
0
0
0
0
0
0
DK391
0
3
0
3
0.06
1
0
0
0
0
0
0
PR38A79
2
7
0
9
0.18
2
0
2
0
0
0
0
NF4217
0
11
0
11
0.22
2
0
1
0
0
0
0
NKALTIUS
1
14
0
15
0.3
4
0
0
0
0
0
0
DKC3511
4
11
1
16
0.32
6
0
0
0
0
0
0
DK315
EE3802
(DKC 4082)
1
19
1
21
0.42
1
0
0
0
0
0
0
0
11
0
11
0.22
0
0
0
0
0
0
NF3715
2
20
0
22
0.44
6
0
0
0
0
0
0
PR39D81
4
21
0
25
0.5
10
0
0
0
0
0
0
DKC3511
1
19
0
20
0.4
3
0
0
0
0
0
0
Average number per plant
270
0.31
Table 38. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Borovce, Slovakia. Date of
observation: September 12, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
Hybrid
DKC3511
2
12
4
DKC
YG
Broken stalks
caused by
Fusarium
ON
spp.
ON
sum
sum/50
18
0.36
2
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
0
0
0
0
0
0
Rust
3512
0
0
0
0
0
0
0
0
0
0
0
0
EF4503
2
9
4
15
0.3
1
0
0
0
1
0
0
DK 315
DKC
3946YG
0
14
2
16
0.32
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
EE4605
1
6
2
9
0.18
1
0
0
0
1
0
0
DK440
2
16
1
19
0.38
3
0
0
0
0
0
0
DKC
4442YG
0
0
0
0
0
0
0
0
0
1
0
0
NE4610
1
10
3
14
0.28
4
0
0
0
0
0
0
PR37D25
0
22
1
23
0.46
2
0
0
0
1
0
0
DKC3511
0
7
2
9
0.18
1
0
0
0
0
0
0
EF4706
0
11
0
11
0.22
1
0
0
0
0
0
0
DKC4490
2
4
2
8
0.16
2
0
0
0
0
0
0
EG4405
0
7
1
8
0.16
0
0
0
0
0
0
0
DKC4626
3
11
3
17
0.34
5
0
0
0
0
0
0
DKC4627YG
0
0
0
0
0
0
0
0
0
0
0
0
NK Thermo
8
16
3
27
0.54
16
0
0
0
0
0
0
DKC4964
2
8
2
12
0.24
5
0
0
0
1
0
0
NF4726
1
11
3
15
0.3
6
0
0
0
0
0
0
DKC3511
0
11
2
13
0.26
5
0
0
0
0
0
0
Average number per plant
271
0.23
Table 39. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Jacovce, Slovakia. Date of
observation: October 17, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust
– Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DKC3511
7
6
6
19
0.38
3
0
0
0
2
0
0
DKC4490
2
20
1
23
0.46
0
0
0
0
0
0
0
EF4503
5
9
7
21
0.42
3
0
0
0
0
0
0
EE4605
6
12
1
19
0.38
1
0
0
0
0
0
0
DK440
5
11
2
18
0.36
1
0
0
1
1
0
0
NE4610
3
14
0
17
0.34
0
0
0
0
0
0
0
DKC3511
4
23
5
32
0.64
4
0
0
0
1
0
EG4405
1
14
1
16
0.32
1
0
0
0
0
0
0
DKC4626
3
14
7
24
0.48
2
0
0
0
0
0
0
PR37D25
6
25
2
33
0.66
4
0
0
0
4
0
0
NF4726
14
14
5
33
0.66
5
0
0
0
1
0
0
DKC4964
2
12
3
17
0.34
0
0
2
0
3
0
0
NK Thermo
2
15
7
24
0.48
3
0
1
0
0
0
0
EF4706
3
15
5
23
0.46
2
0
1
0
0
0
0
DKC3511
8
11
4
23
0.46
2
0
0
0
0
0
0
Average number per plant
272
sum/50
Helicoverpa
DVV
adults
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
0.46
Rust
Table 40. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Šaľa II., Slovakia. Date of
observation: September 12, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
sum/50
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
0
0
0
0
0
0
5
0
0
6
0
0
0
0.32
4
0
0
0
0
0
0
22
0.44
1
0
0
0
0
0
0
19
0.38
4
0
0
0
0
0
0
4
28
0.56
3
0
0
3
0
0
0
8
5
17
0.34
3
0
0
0
0
0
0
0
0
0
0
0
0
0
0
18
0
0
0
DKC3511
5
8
3
16
0.32
7
0
0
0
0
0
0
NE4610
0
15
2
17
0.34
5
0
0
2
0
0
0
DK440
DKC
4442YG
5
5
6
16
0.32
6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
11
0
0
0
NF4726
6
12
2
20
0.4
9
0
0
0
0
0
0
DKC4626
0
21
1
22
0.44
5
0
0
9
0
0
0
DKC4627YG
0
0
0
0
0
0
0
0
0
0
0
0
NK Thermo
0
3
1
4
0.08
0
0
0
2
0
0
0
EF4706
4
12
4
20
0.4
8
0
0
0
0
0
0
DKC3511
0
18
0
18
0.36
3
0
0
13
0
0
0
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
DKC3511
2
17
1
20
0.4
8
PR37D25
0
30
0
30
0.6
EG4405
4
8
4
16
DKC4490
1
15
6
EF4503
1
11
7
DKC4964
1
23
EE4605
4
DKC
YG
3512
Average number per plant
273
Rust
0.32
Table 41. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Smolinské, Slovakia. Date of
observation: September 17, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
sum/50
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3
0.06
0
0
0
0
0
0
0
0
2
0.04
0
0
0
0
0
0
0
5
2
11
0.22
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
5
4
13
0.26
0
0
0
0
0
0
0
PR37D25
1
10
0
11
0.22
0
0
0
0
1
0
0
DKC3511
2
4
2
8
0.16
0
0
0
0
0
0
0
EE4605
0
4
1
5
0.1
0
0
0
0
0
0
0
NK Thermo
0
10
1
11
0.22
0
0
0
0
0
0
0
EF4706
0
1
0
1
0.02
0
0
0
0
0
0
0
DKC4490
4
4
4
12
0.24
0
0
0
0
0
0
0
NE4610
0
2
2
0.04
0
0
1
0
0
0
0
DKC3511
0
1
5
0.1
0
0
0
0
0
0
0
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
DKC3511
1
2
3
6
0.12
0
EG4405
0
5
0
5
0.1
0
DKC4626
2
1
4
7
0.14
DKC4627YG
0
0
0
0
DKC4964
1
2
0
NF4726
0
2
DK440
4
DKC
4442YG
EF4503
Average number per plant
274
4
0.12
Rust
Table 42. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Bardoňovo, Slovakia. Date of
observation: September 9, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
sum/50
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
0
1
0
0
0
0
2
0
2
0
0
0
0
0.46
6
0
2
0
0
0
0
25
0.5
5
0
5
0
0
0
0
7
27
0.54
12
0
2
0
0
0
0
7
33
0.66
15
0
0
0
0
0
0
15
8
28
0.56
9
0
0
0
0
0
0
2
18
6
26
0.52
6
0
4
0
0
0
0
DKC3511
4
12
7
23
0.46
8
0
1
0
0
0
0
EF4706
1
19
4
24
0.48
10
0
0
0
0
0
0
ED 3825
1
17
11
29
0.58
7
0
0
0
0
0
0
EE4605
1
18
4
23
0.46
4
0
0
0
0
0
0
DKC4490
10
9
6
25
0.5
11
0
0
0
0
0
0
NE4610
1
15
4
20
0.4
4
0
2
0
0
0
0
DKC3511
4
22
2
28
0.56
4
0
0
0
0
0
0
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
DKC3511
3
9
3
15
0.3
4
DKC4626
2
18
1
21
0.42
NF4726
5
12
6
23
EG4405
1
19
5
DKC4964
5
15
NFT 2412
4
22
DK440
5
EF4503
Average number per plant
275
0.49
Rust
Table 43. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Palárikovo, Slovakia. Date of
observation: September 11, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
sum/50
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
0
2
1
0
0
0
2
0
1
0
0
0
0
0.48
2
0
2
0
0
0
0
20
0.4
4
0
0
0
0
0
0
11
27
0.54
6
0
0
0
0
0
0
12
20
0.4
4
0
0
0
0
0
0
10
11
29
0.58
1
0
0
0
0
0
0
7
4
15
26
0.52
7
0
1
0
0
0
0
EF4503
8
1
10
19
0.38
2
0
0
0
0
0
0
EG4405
9
4
9
22
0.44
4
0
1
0
0
0
0
DK440
4
4
10
18
0.36
3
0
0
0
0
0
0
EE4605
6
6
5
17
0.34
2
0
0
0
0
0
0
DKC4626
2
12
5
19
0.38
1
0
0
0
0
0
0
NE4610
4
7
5
16
0.32
0
0
0
0
0
0
0
DKC3511
3
8
7
18
0.36
1
0
1
0
0
0
0
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
DKC3511
9
3
8
20
0.4
6
NF4726
2
6
15
23
0.46
DKC4490
6
2
16
24
NK thermo
4
5
11
EF4706
9
7
DKC4964
5
3
PR37D25
8
DKC3511
Average number per plant
276
0.42
Rust
Table 44. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Šaľa I., Slovakia. Date of
observation: September 12, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
sum/50
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
0
0
0
0
0
0
4
0
0
0
0
0
0
0.42
9
0
0
0
0
0
0
0.38
4
0
0
0
0
0
0
20
0.4
2
0
0
0
0
0
0
23
0.46
2
0
0
0
0
0
0
1
18
0.36
6
0
0
0
0
0
0
17
1
18
0.36
4
0
0
0
0
0
0
6
10
4
20
0.4
4
0
1
0
0
0
0
1
14
2
17
0.34
3
0
0
0
0
0
0
NE4711
4
5
4
13
0.26
6
0
0
0
0
0
0
DKC4490
1
6
3
10
0.2
1
0
0
0
0
0
0
DKC5143
DKC
5018YG
4
5
4
13
0.26
4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
DKC4888
4
13
3
20
0.4
8
0
0
0
0
0
0
DKC4964
1
6
1
8
0.16
1
0
0
0
0
0
0
NFC 2212
4
10
6
20
0.4
7
0
0
0
0
0
0
EG4707
2
11
4
17
0.34
2
0
0
0
0
0
0
DKC5143
0
14
4
18
0.36
0
0
0
0
0
0
0
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
DKC5143
6
7
10
23
0.46
4
EF4810
0
16
2
18
0.36
DKC4983
8
10
3
21
DKC5170
1
17
1
19
ED 3873
3
11
6
EG4911
1
17
5
EG5009
7
10
ED 3679
0
DKC4889
EF4705
Average number per plant
277
0.33
Rust
Table 45. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Nitra, Slovakia. Date of observation:
September 12, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust –
Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
DKC5143
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
5
9
12
26
0.52
DKC4983
5
6
9
20
EF4810
12
9
9
30
DKC4889
3
4
23
NE4711
4
9
DKC4964
11
EG4911
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
3
0
3
0
0
0
0
0.4
6
0
1
0
0
0
0
0.6
11
0
2
0
0
0
0
30
0.6
0
0
2
0
0
0
0
6
19
0.38
0
0
0
0
0
0
0
6
10
27
0.54
10
0
0
0
0
0
0
4
9
8
21
0.42
2
0
0
0
0
0
0
DKC4888
8
12
12
32
0.64
3
0
1
0
0
0
0
DKC5170
10
10
10
30
0.6
6
0
0
0
0
0
0
PR37F73
5
5
9
19
0.38
6
0
2
0
0
0
0
NKCISKO
2
2
5
9
0.18
3
0
3
0
0
0
0
DKC4490
6
6
9
21
0.42
3
0
3
0
0
0
0
DKC5143
DKC
5018YG
6
10
5
21
0.42
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
EG4707
2
8
7
17
0.34
2
0
1
0
0
0
0
EG5009
3
8
14
25
0.5
2
0
3
0
0
0
0
PR38A79
6
10
12
28
0.56
8
0
0
0
0
0
0
EF4705
8
6
8
22
0.44
5
0
1
0
0
0
0
DKC5143
6
4
6
16
0.32
5
0
0
0
0
0
0
Average number per plant
278
0.43
Table 46. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Veľký Meder, Slovakia. Date of
observation: September 3, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
DKC5143
6
19
4
29
0.58
DKC4490
0
13
4
17
DKC4888
6
10
4
20
EF4810
1
8
3
NE4711
2
9
DKC4889
3
EG4911
DKC4983
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
10
0
0
0
0
0
0.34
7
0
0
0
0
0
0.4
15
0
0
0
0
0
2
12
0.24
3
0
0
0
1
0
0
3
14
0.28
8
0
0
0
0
0
1
11
5
19
0.38
4
0
0
0
0
0
2
4
13
5
22
0.44
12
0
0
0
0
0
4
2
12
2
16
0.32
3
0
0
0
0
0
0
DKC5170
8
9
8
25
0.5
13
0
0
0
0
0
3
PR36D79
5
13
2
20
0.4
14
0
0
0
0
0
1
PR37F73
2
8
0
10
0.2
4
0
0
0
0
0
0
EG4707
0
22
4
26
0.52
4
0
0
0
0
0
0
DKC5143
10
8
4
22
0.44
12
0
0
0
0
0
4
EG5009
1
19
2
22
0.44
3
0
0
0
0
0
0
CISKO
3
13
3
19
0.38
6
0
0
0
0
0
3
EF4705
0
16
5
21
0.42
5
0
0
0
0
0
0
DKC4964
7
9
4
20
0.4
10
0
0
0
0
0
3
DKC5143
0
21
9
30
0.6
3
0
0
0
0
0
0
Average number per plant
279
0.40
3
Table 47. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Matuškovo, Slovakia. Date of
observation: September 11, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera,
Rust – Puccinia spp., ON/50 - average number of ON damages per plant.
Damage caused by ON
larvae
above
ear
below ear
sum/50
Helicoverpa
Damage caused by
Ustilago Helminthosp.
spp.
spp.
zea damage
DVV
adults
0
0
0
0
0
0
2
0
0
0
4
0
0
0.32
3
0
0
0
2
0
0
21
0.42
2
0
0
0
1
0
0
3
21
0.42
4
0
0
0
2
0
0
6
4
10
0.2
0
0
2
0
0
0
0
12
4
18
0.36
2
0
0
0
1
0
0
13
6
19
0.38
2
0
1
0
0
0
0
6
12
2
20
0.4
6
0
0
0
0
0
0
1
6
2
9
0.18
0
0
0
0
1
0
0
PR37F73
4
15
3
22
0.44
6
0
0
0
1
0
0
DKC4964
0
13
3
16
0.32
1
0
0
0
2
0
0
EG5009
8
12
4
24
0.48
3
0
0
0
0
0
0
DKC5143
0
15
3
18
0.36
1
0
0
0
0
0
0
DKC4889
7
8
8
23
0.46
6
0
0
0
0
0
0
EF4705
0
11
3
14
0.28
0
0
1
0
0
0
0
DKC4888
5
16
7
28
0.56
1
0
0
0
0
0
0
DKC5143
0
17
5
22
0.44
0
0
0
0
0
0
0
Hybrid
ON
sum
Broken stalks
caused by
Fusarium
ON
spp.
DKC5143
4
13
6
23
0.46
4
PR36D79
2
16
1
19
0.38
DKC4983
3
7
6
16
EG4707
0
14
7
CISKO
4
14
EF4810
0
DKC4490
2
NE4711
0
DKC5170
EG4911
Average number per plant
280
0.38
Rust
Table 48. Number of damages caused by different pests and population density of pest larvae
or adults observed on 50 plants of each hybrid. Locality Kameničná, Slovakia. Date of
observation: October 5, 2009. ON – O. nubilalis, DVV – Diabrotica virgifera virgifera, Rust
– Puccinia spp., ON/50 - average number of ON damages per plant.
Hybrid
Damage caused by ON
larvae
above
ear
below ear
ON
sum
sum/50
DKC5143
3
4
4
11
0.22
EG4707
4
4
6
14
DKC4983
9
5
4
18
DKC5170
6
8
5
EF4810
6
7
PR37F73
7
NE4711
DKC4964
Broken stalks
caused by
Fusarium
ON
spp.
Helicoverpa
zea damage
DVV
adults
Damage caused by
Ustilago Helminthosp.
spp.
spp.
Rust
2
0
1
0
0
0
0
0.28
4
0
0
0
0
0
0
0.36
12
0
0
0
0
0
0
19
0.38
8
0
0
0
0
0
3
8
21
0.42
5
0
0
0
0
0
0
4
4
15
0.3
7
0
0
0
0
0
0
9
5
4
18
0.36
6
0
0
0
0
0
0
4
4
7
15
0.3
9
0
1
0
0
0
0
PR36D79
8
12
7
27
0.54
13
0
0
0
0
0
5
EG5009
5
5
7
17
0.34
5
0
1
0
0
0
0
DKC4888
7
5
5
17
0.34
8
0
0
0
0
0
0
DKC5143
5
4
5
14
0.28
4
0
1
0
0
0
0
EF4705
7
10
7
24
0.48
6
0
0
0
0
0
0
CISKO
12
8
4
24
0.48
14
0
0
0
0
0
1
EG4911
4
8
11
23
0.46
4
0
0
0
0
0
0
DKC4490
5
5
3
13
0.26
7
0
0
0
1
0
3
DKC4889
4
4
4
12
0.24
3
0
0
0
0
0
0
DKC5143
8
10
5
23
0.46
8
0
0
0
0
0
0
Average number per plant
281
0.36
10.2. Influence of microsporidian infection caused by Nosema pyrausta from
Slovakia on populations of O. nubilalis from various countries.
Table 62. Comparision of bionomy between the un - infected population Aachen Germany
(1) and infected population with spores of N. pyrausta Aachen (2), test 1.
Date of hatch
N. pyrausta spores added
Pupae observations
Sum of pupae
Moths eclosion
Sum of moths
Egg masses
Sum of egg masses
282
Population Aachen Germany 50
larvae (1)
17.-18. 1. 2006
14. 2. 5 pupae
17.2. 1 pupa
20.2. 9 pupae
22.2. 4 pupae
3.3. 3 pupae
22 pupae
21.2. 2M
22.2. 2F
28.2. 3M+3F
29.2. 2M+4F
2.3. 2M+1F
6.3. 1M+2F
10M+12F =22 moths
29.2. 12 masses
2.3. 2 masses
6.3. 5 masses
19 masses
Population Aachen Germany 50
larvae (2)
17.-18. 2006
24.1.2006
14. 2. 13 pupae
17. 2. 4 pupae
20.2. 4 pupae
22.2. 5 pupae
29.2. 3 pupae
29 pupae
20.2. 1M+2F
21.2. 1F
22.2. 3M+1F
29.2. 1M
2.3. 6M+3F
3.3.1F
11M+8F =19 moths
22. 2. 7 masses
28.2. 13 masses
3.3. 3 masses
6.3. 5 masses
7.3. 2 masses
30 masses
Table 63. Comparision of bionomy between the un - infected population Aachen Germany
(1) and infected population with spores of N. pyrausta Aachen (2), test 2.
Date of hatch
N. pyrausta spores added
Pupae observations
Population Aachen Germany 50
larvae (1)
20.2. 2006
8.3. 2 pupae
13.3. 4 pupae
14.3. 5 pupae
15.3. 2 pupa
20.3. 2 pupae
22.3. 3 pupae
24.3. 2 pupae
30.3. 4 pupae
4.4. 1 pupa
Sum of pupae
Moths eclosion
25 pupae
Sum of moths
Egg masses
16M+7F=23moths
22.3. 2 masses
23.3. 3 masses
24.3. 10 masses
27.3. 15 masses
30.3. 3 masses
31.3. 7 masses
3.4. 4 masses
4.4. 4 masses
10.4. 2 masses
50 masses
Sum of egg masses
283
20.3. 3M+1F
22.3. 5M+3F
23.3. 2M+1F
24.3. 1M
27.3. 3M+1F
30.3. 1M
31.3. 1M+1F
Population Aachen Germany 50
larvae (2)
20.2. 2006
28.2. 2006
13.3. 4 pupae
14.3. 2 pupae
20.3. 4 pupae
23.3. 4 pupae
24.3. 3 pupae
30.3. 2 pupa
4.4. 1 pupa
5.4. 1 pupa
12.4. 2 pupae
23 pupae
20.3. 4M+1F
22.3. 3F
23.3. 2M
24.3. 2F
27.3. 3M+1F
28.3. 1F
30.3. 1M+1F
10.4. 1M+1F
19.4. 1M+1F
12M+11F=23moths
27.3. 5 masses
28.3. 8 masses
30.3. 4 masses
31.3. 4 masses
3.4. 9 masses
19.4. 4 masses
34 masses
Table 64. Comparing of the bionomy between un - infected population Slovakia * Romania
(1) and infected population with spores of N. pyrausta Slovakia * Romania (2).
Date of hatch
N. pyrausta spores added
Pupae observations
Sum of pupae
Moths eclosion
Sum of moths
Egg masses
Sum of egg masses
284
Population Slovakia*Romania 50
larvae (1)
18.1.2006
7.2. 1 pupa
14.2. 10 pupae
17.2. 15 pupae
20.2. 10 pupae
24.2. 5 pupae
28.2. 8 pupae
49 pupae
17.2. 1M+2F
20.2. 8M+8F
24.2. 10M+4F
28.2. 9M+7F
28M+21F =49 moths
14.2. 5 masses
17.2. 4 masses
20.2. 10 masses
24.2. 8 masses
27 masses
Population Slovakia*Romania 50
larvae (2)
18.1.2006
19.1.2006
14.2. 12 pupae
17.2. 6 pupae
20.2. 2 pupae
28.2. 2 pupae
3.3. 1 pupa
6.3. 1 pupa
24 pupae
20.2. 1M+2F
21.2. 1M+3F
24.2. 3M+3F
5M+8F = 13 moths
21.2. 1 mass
3.3. 3 masses
8.3. 1 mass
5 masses
Table 65. Comparing of the bionomy between un - infected population Slovakia (1) and
infected population with spores of N. pyrausta Slovakia (2).
Date of hatch
N. pyrausta spores added
Pupae observations
Population Slovakia 50 larvae (1)
4.3. 2006
20.3. 4 pupae
22.3. 2 pupae
23.3. 6 pupae
24.3. 2 pupae
28.3. 1pupa
30.3. 2 pupae
5.4. 2 pupae
Popultion Slovakia 50 larvae (2)
4.3. 2006
7.3. 2006
20.3. 1 pupa
24.3. 1 pupa
28.3. 2 pupae
30.3. 9 pupae
Sum of pupae
Moths eclosion
19 pupae
Sum of moths
Egg masses
4F= 4 moths
28.3. 1M
30.3. 1M
3.4. 1M
5.4. 1M+1F
4M+1F= 5 moths
Sum of egg masses
0
0
285
13 pupae
28.3. 2F
3.4. 1F
5.4. 1 F
Table 66. Comparing of the bionomy between un - infected population Austria (1) and
infected population with spores of N. pyrausta Austria (2).
Date of hatch
N. pyrausta spores added
Pupae observations
Sum of pupae
Moths eclosion
Sum of moths
Egg masses
Sum of egg masses
286
Population Austria 50 larvae (1)
23.2. 2006
20.3. 6 pupae
13.3. 1 pupa
22.3. 5 pupae
23.3. 4 pupae
30.3. 5 pupae
31.3. 3 pupae
3.4. 4 pupae
4.4. 2 pupae
5.4. 3 pupae
6.4. 5 pupae
12.4. 2 pupae
40 pupae
23.3. 1M
27.3. 2M+5F
28.3. 1M+1F
31.3. 3M+2F
3.4. 7M+6F
4.4. 1M+2F
5.4. 2M+1F
10.4. 2M+2F
19.4. 1F
19M+20F=39 moths
3.4. 7 masses
4.4. 11 masses
5.4. 4 masses
7.4. 5 masses
10.4. 5 masses
32 masses
Population Austria 50 larvae (2)
23.2. 2006
28.2. 2006
20.3. 7 pupae
22.3. 3 pupae
23.3. 6 pupae
24.3. 3 pupae
27.3. 3 pupae
30.3. 7 pupae
4.4. 1 pupa
5.4. 3 pupae
11.4. 2 pupae
19.4. 3 pupae
38 pupae
27.3. 1M
28.3. 2M+1F
31.3. 1M+1F
3.4. 4M+3F
4.4. 1M+1F
5.4. 2F
10.4. 1M+3F
11.4. 1M+1F
11M +12F=23 moths
31.3. 5 masses
3.4. 12 masses
10.4. 4 masses
11.4. 2 masses
23 masses
Table 67. Comparing of the bionomy between un - infected population Serbia (1) and infected
population with spores of N. pyrausta Serbia (2).
Date of hatch
N. pyrausta spores added
Pupae observations
Sum of pupae
Moths eclosion
Sum of moths
Egg masses
Sum of egg masses
287
Population Serbia 50 larvae (1)
16.2. 2006
8.3. 4 pupae
9.3. 2 pupae
13.3. 18 pupae
14.3. 3 pupae
15.3. 1 pupa
22.3. 1 pupa
5.4. 1 pupa
10.4. 2 pupae
12.4. 2 pupae
34 pupae
14.3. 1M+1F
15.3. 3F
16.3. 2M+4F
20.3. 10M+4F
22.3. 1M
23.3. 1M
31.3. 1M
3.4. 1F
5.4. 1M
10.4. 2F
19.4. 1M+1F
18M+16F=34moths
0
Population Serbia 50 larvae (2)
16.2. 2006
20.2. 2006
8.3. 1 pupa
13.3. 1 pupa
14.3. 3 pupae
16.3. 4 pupae
20.3. 3 pupae
23.3. 1 pupa
24.3. 2 pupae
30.3. 2 pupae
11.4. 1 pupa
19.4. 1 pupa
19 pupae
20.3. 2M+1F
21.3. 1M+1F
22.3. 2M
30.3. 1M+1F
31.3. 1M
7M+3F=10moths
0
Table 68. Obtained measure characteristics of fifth instar O. nubilalis larvae and pupae in
uninfected and infected German population with spores of N. pyrausta.
Germany
(population)
Weight of larvae
(g)
0.1510
0.988
0.1325
0.0884
0.0865
0.1020
0.1121
0.0978
0.1321
0.1401
0.1051
0.1090
0.0695
0.0713
0.0606
0.0629
0.0701
0.0583
0.1001
0.0671
Size
(mm)
23
18
19
22
18
20
15
22
15
20
20
21
17
19
17
19
18
19
19
20
Weight of pupae
(g)
0.0774
0.0734
0.0497
0.0787
0.0935
0.0333
0.0777
0.1210
0.0773
0.0912
0.0832
0.0372
0.0696
0.0515
0.0701
0.0806
0.0651
0.0761
0.0800
0.0711
Germany + N. pyrausta
(population)
Weight of larvae
Size
(g)
(mm)
0.1487
19
0.0769
21
0.0882
20
0.0933
20
0.9931
21
0.0575
14
0.1280
20
0.0919
17
0.0762
15
0.0633
18
0.1121
23
0.0665
19
0.0397
15
0.1170
22
0.0574
19
0.0571
15
0.0698
16
0.0542
17
0.0600
18
0.0506
19
Weight of pupae
(g)
0.0579
0.1318
0.0863
0.0838
0.0835
0.0820
0.1229
0.1015
0.0369
0.0749
0.0426
0.0684
0.0626
0.0747
0.0530
0.0181
0.0505
0.0292
0.0579
0.0707
Table 69. Obtained measure characteristics of fifth instar O. nubilalis larvae and pupae in
uninfected and infected Slovakia * Romania population with spores of N. pyrausta.
Slovakia * Romania
Weight of larvae
Size
(g)
(mm)
0.0717
23
0.1372
23
0.0897
20
0.1211
21
0.1043
24
0.0863
13
0.1010
20
0.0626
20
0.1049
16
0.0815
14
288
Weight of pupae
(g)
0.0682
0.0774
0.0611
0.0621
0.0688
0.0990
0.0475
0.0790
0.0577
0.065
Slovakia * Romania + N. pyrausta
Weight of larvae
Size
Weight of pupae
(g)
(mm)
(g)
0.0510
18
0.0699
0.0664
15
0.0909
0.0666
14
0.0621
0.0665
15
0.1001
0.0533
15
0.0721
0.0777
14
0.0790
Table 70. Obtained measure characteristics of fifth instar O. nubilalis larvae and pupae in
uninfected and infected Slovakia population with spores of N. pyrausta.
Slovakia
Weight of larvae
(g)
0.1231
0.0917
0.1421
0.0765
0.0918
0.1078
0.1028
0.0794
0.0735
0.0615
0.1001
0.1000
0.0368
0.0799
0.0765
0.0763
0.0325
0.0762
0.1002
0.0988
289
Size
(mm)
25
19
16
17
20
20
20
17
18
15
20
19
17
22
21
19
18
17
15
17
Weight of pupae
(g)
0.0881
0.0949
0.1065
0.0875
0.0775
0.0811
0.1000
0.0605
0.0781
0.0781
0.0862
0.0274
0.0991
0.0319
0.0326
0.0629
0.0326
0.0992
0.0700
0.0342
Slovakia + N. pyrausta
Weight of larvae
Size
(g)
(mm)
0.0942
19
0.0832
20
0.1054
18
0.0703
13
0.0971
18
0.0932
17
0.0850
16
0.0919
19
0.0484
18
0.0978
18
0.0791
19
0.0690
18
0.0799
20
0.0800
17
0.1198
20
0.0608
15
0.0918
18
0.0704
17
0.0525
15
0.0499
16
Weight of pupae
(g)
0.0713
0.0711
0.0412
0.0724
0.0617
0.0743
0.0723
0.0677
0.0605
0.0399
0.0711
0.0671
0.0587
0.0725
0.0716
0.0587
0.0722
0.0678
0.0605
0.0400
Table 71. Obtained measure characteristics of fifth instar O. nubilalis larvae and pupae in
uninfected and infected Austria population with spores of N. pyrausta.
Austria
Weight of larvae
(g)
0.1035
0.1136
0.1082
0.0973
0.0843
0.0770
0.1191
0.0811
0.0870
0.0794
0.0702
0.0754
0.0101
0.0680
0.0334
0.0792
0.0685
0.0766
0.0668
0.0538
290
Size
(mm)
15
21
24
17
17
18
22
21
15
15
19
18
20
15
15
19
20
18
17
16
Weight of pupae
(g)
0.0626
0.0865
0.0938
0.0803
0.0672
0.0438
0.0662
0.0788
0.0899
0.0817
0.0712
0.0756
0.0710
0.0726
0.0769
0.0389
0.0728
0.0771
0.0606
0.0595
Austria + N. pyrausta
Weight of larvae
Size
(g)
(mm)
0.0908
20
0.1124
23
0.0880
20
0.1015
16
0.0886
20
0.0813
18
0.1148
19
0.0923
17
0.0758
19
0.0856
16
0.1143
23
0.0950
20
0.0439
15
0.0709
18
0.0892
19
0.0537
17
0.1212
20
0.1100
20
0.0719
16
0.0728
18
Weight of pupae
(g)
0.0626
0.0865
0.0938
0.0803
0.0672
0.0438
0.0662
0.0788
0.0899
0.0817
0.0646
0.0583
0.0953
0.0782
0.0721
0.0686
0.0756
0.0670
0.0566
0.0777
Table 72. Obtained measure characteristics of fifth instar O. nubilalis larvae and pupae in
uninfected and infected Serbia population with spores of N. pyrausta.
Serbia
Weight of larvae
(g)
0.0652
0.0592
0.1120
0.0943
0.0926
0.0888
0.1216
0.0817
0.1111
0.0912
0.0651
0.0616
0.1011
0.0941
0.0919
0.0788
0.1109
0.0817
0.0911
0.1101
291
Size
(mm)
22
20
20
16
13
15
16
17
21
15
20
22
21
17
15
17
15
17
21
17
Weight of pupae
(g)
0.0698
0.0718
0.0540
0.0941
0.0614
0.0995
0.0477
0.0633
0.0518
0.0513
0.0697
0.0715
0.0770
0.0929
0.0716
0.0999
0.0579
0.0709
0.0511
0.0515
Serbia + N. pyrausta
Weight of larvae
Size
(g)
(mm)
0.0833
23
0.0385
24
0.0550
18
0.1015
22
0.1536
19
0.0994
18
0.0741
14
0.0615
17
0.0712
19
0.0399
22
0.0907
20
0.1113
21
0.0810
20
0.1001
17
0.0886
19
0.0812
20
0.1128
15
0.0913
19
0.0871
17
0.0751
15
Weight of pupae
(g)
0.0736
0.0779
0.0855
0.0624
0.0724
0.0664
0.0591
0.0741
0.0920
0.0556
0.0792
0.0781
0.0529
0.0783
0.0662
0.0865
0.0773
0.0795
0.0675
0.0527
292