STUDY OF LIFE CYCLE OF THE FIG WAX SCALE INSECT
CEROPLASTES RUSCI (LINNAEOUS)
(HOMOPTERA:
COCCIDAE) AND THE PREDATORY ACTIVITY OF
EUBLEMMA SCITULA (RAMB.)UNDER THREE DIFFERENT
ENVIRONMENTAL CONDITIONS.
BY
ADEL, A. ABOU EL- ELA
ZOOLOGY DEPT., FAC. SCI., FAYOUM UNIVERSITY
UNIVERSITY2
Abstract
The fig wax scale insect Ceroplastes rusci (Linnaeus) is a serious pest
of fruit in many countries. In this study we investigated the efficacy
of an endemic predacious moth, Eublemma scitula (Ramb.), as a
potential biocontrol agent. Captive breeding trails found E. scitula to
be efficient predators against C. rusci, but unusual hyperactive trait
in early instars of E. scitula resulted in lower than expected survival
rates. Also, captive populations of C. rusci were established to record
life history parameters at three different conditions and its moth
predator. The implications of this trait in terms of the laboratory
environment, augmentative release protocol and as a survival
strategy also are discussed.
Key words: Eublemma scitula, biocontrol, scale insects, life history.
Introduction
The fig wax scale insect, Ceroplastes rusci L. (Homoptera: Coccidae)
is considered a serious pest of fig (Tranfaglia, 1981 in Italy;
Fernandes, 1981- 82 in Portugal; Onder and Soydanbay, 1984 in
Turkey; Carles, 1985 in France and Fazeli & Farzneh, 1993 in Iran)
and other fruit trees in many countries (Nga et.al, 2006 in South- east
Vietnam, Hammad, 2006 in Egypt, Morsi and Mousa, 2004 in Egypt).
This insect causes weakening the trees by sucking the sap from
leaves, branches and fruits. Its main damage is due to the
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development of various sooty mould fungi on the honey dew
secretion, which covers leaves, branches and fruits. This mould sticks
firmly on the surface of the plant and thus it marks the fruit
rendering it unmarketable (Hammad, 2006, Elmer & Brawner 1975
and McGavin 1993). In addition to the physical damage caused to the
plants, many scale insects, including C. rusci, are known to carry
plant viruses (La Notte et.al 1997). According to Smith (1986); the
application of insecticides is frequently followed by recurrent
infestation. Therefore, during the past decade, intensive efforts have
been done to improve the biological control in many countries,
searching the well established and most efficient biological agents
should be involved (Hendawy,1999). Ceroplastes species may be
controlled with a range of commercial chemical sprays, but biological
control methods are preferable due to the undesirable side effects of
pesticides use. Furthermore, pesticides are not always efficient if they
are washed away by unpredictable rains or if they do not act against
all life stages of the target pest. Many species of Ceroplastes,
including C.rusci, have been controlled successfully with range of
classical and augmentative biocontrol agents, including the wasp
parasitoids Coccophagus lycimnia Walker(Aphelinidae), Scutellista
cyanea Motschulsky (Pteromalidae) (Argriou& Mourikis 1981) and
Anicetus beneficus Ishii and Yasumatsu (Encyrtidae) (Smith 1986).
So, this paper details the life history of C. rusci and E. scitula under
three different environmental conditions from temperature and
relative humidity. Also, presents the results of biocontrol experiments
using the indigenous biological agent, E. scitula and its the predation
rates for larvae when feeding on the C. rusi. Finally, study the
fecundity of E. scitula measured on four different hosts species.
Materials and methods
1- Life cycle of C. rusci:A captive population of C.rusci was established , where insects were
reared on fig in net house measuring 2.25m × 1.5m × 1.75m high.
To gauge the range of variability in life cycle characters, three
breeding experiments were conducted using 100 individuals of C.
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rusci at three different environmental conditions (temperature and
relative humidity). Several parameters of the biological aspects were
measured, including longevity, survival rate and fecundity. Survival
rate was determined as the proportion of adult imagines surviving in
each experiment after completing their life cycle in captivity.
Fecundity was measured for 40 individuals. Daily temperature and
relative humidity (RH.) readings were taken, each record being the
mean of three readings taken at 7.30, 13.30 and 19.30 hours.
Temperature and RH. per experiment is the average of all breeding
days.
2- Life cycle of E.scitula :Adults of the predaceous moth E. scitula were mated and encouraged
to lay eggs following the method detailed by Nga et. al. (2006), where
the fecundity was measured for 30 individuals. E. scitula feeding
trials were carried out in the laboratory under ambient conditions in
plastic boxes measuring 13 cm × 8 cm × 5cm high. Eggs were collected
on green-black clothes and attached to fresh fig shoots infested with
C. rusci. Additional fresh shoots with C. rusci were placed in the box
each when survival and predation rates were recorded. Predation
rates of E. scitula final instar larvae feeding on on C. rusci at three
different conditions from temperature and relative humidity were
corrected to Abbott's formula (Abbott 1925). All stages of E. scitula
life cycle were measured when feeding on the alternate host
Planococcus lilacinus (Cockerel), Dismicoccous brevipes and
Pulvinaria sp., as these were more readily available and could
support greater number of E. scitula. Three batches of 90 – 100 E.
scitula were bred through to final instar larvae and adults in plastic
boxes measuring 20 × 20 ×8 cm high under laboratory conditions in
which the availability of food was not a limiting factor.
Results
Data recorded in table (1) shows the timing of C. rusci life stages
and females fecundity in captivity under three different
environmental conditions (temperature and relative humidity). There
was a trend for C. rusci growth time at all stages to decrease as
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temperature and relative humidity decrease. The average of total life
cycle of C. rusci took between 75.6 and 86.4 days at the lower and
higher temperature and relative humidity, (Table 1). On the other
hand, the fecundity of females increased gradually with increasing in
the temperature and relative humidity. Where, C. rusci females laid
an average of 1141.5, 1157, and 1167 eggs/ female under three
different environmental l conditions, respectively.
Table (1): Life cycle and fecundity of C. rusci under three
different environmental conditions.
life stage
1st instar
2nd instar
3rd instar
4th instar
Adult stage
Total life cycle
Fecundity
26 ˚C ± 0.5,
(65± 2 RH.)
4.o ± 0.2
18.7 ± 0.8
28.5 ± 0.5
12.4 ± 0.6
12.0 ± 0.1
75.6 ± 0.4
1141.5 ± 9.8
28˚C ± 0.5, (70
± 2 RH.)
4.5 ± 0.5
19.3 ± 0.6
29.9 ± 0.8
13.6 ± 0.1
12.8 ± 0.3
80.1 ± 0.4
1157 ± 5.9
30˚ C ± 0.5, (75
± 2 RH.)
4.7 ± 0.3
19.8 ± 0.4
31.2 ± 0.3
14.2 ± 0.7
13.5 ± 0.6
86.4 ± 0.5
1167 ± 10.6
In addition to the noctuid moth E. scitula, several other natural
enemies of C.rusci were detected in the field, including Orius
albidipennis (Hemiptera: Anthocoridae), Chrysperla carnea
(Neuroptera: Chrysopidae) and Chilocorus bipustulatus L.
(Coleoptera: Coccinellidae). E. scitula was recorded attacking several
other homoptera pest species in the study area, including
Planococcus lilacinus, Dysmicoccus brevipes (Cockerell) (both
Pseudococcidae), Pulvinaria sp. and Crystallotesta sp. (both coccidae).
The fecundity of E. scitula on four potential hosts and the
percentages of eggs hatched are shown in Table 2. In this table, the
number of eggs per E. scitula female on four hosts were 145.8, 115.7,
119.6 and 93.2 egg for C. rusci, P. lilacinus, D. brevipes and Pulvinaria
tenuivalvata , respectively.
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Table (2) Fecundity of Eublemma scitula measured on four different
host species.
Host
Fecundity (n= 40)
Hatching
percentage
C. rusci
P. lilacinus
D. brevipes
145.8 ± 6.2 (108- 170)
115.7 ± 12.7 (45- 162)
119.6 ± 13.9 (47- 174)
88.6 ± 2.5
84.2 ± 2.3
86.3 ± 2.1
P. tenuivalvata
93.2 ± 18.2 (43- 147)
86.6 ± 1.9
Also, the number of eggs hatching percentages of E. scitula laid on
the four different hosts ranged from 84.2 for P.lilacinus to 88.6 % for
C. rusci. The period of all stages of E. scitula reared under three
different conditions when feeding on C. rusci are given in Table 3.
The average life cycle from egg to adult took between 51.8 and 58.1
days. Also, there was a general trend for E. scitula growth periods at
all stages to decrease as the temperature and relative humidity
increased.
Table ( 3 ) Life cycle of E. scitula feeding on C. rusci under
three different environmental conditions.
life stage
Egg
Larva
Prepupa
Pupa
Adult stage
Total life cycle
26 ˚C ± 0.5, (65± 2
RH.)
8.0 ± 0.3
19.1 ± 0.4
6.o ± 0.2
16.0 ± 0.6
9.0 ± 0.1
58.1 ± 0.4
28˚C ± 0.5, (70 ±
2 RH.)
7.5 ± 0.3
18.1 ± 0.6
5.3 ± 0.2
15.1 ± 0.1
8.0 ± 0.5
54.0 ± 0.3
30˚ C ± 0.5, (75 ±
2 RH.)
7.3 ± 0.2
17.8 ± 0.4
5.1 ± 0.7
14.0 ± 0.2
7.5 ± 0.6
51.8 ± 0.5
Table (4) describes the predation rates for final instar E. scitula
larvae feeding on C. rusci under three different conditions. The
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average daily consumption of C. rusci by final instar E. scitula larvae
was 26. (n=90), with mean corrected mortality of C. rusci at 86.7%.
Final instar E.scitula larvae entered the prepupal phase on day five.
Also, the rate of predation increase with increasing in the
temperature and relative humidity. Finally, rate of predation for E.
scitula larvae feeding on C.rusci at three different conditions increase
from first day till third day and then decrease at the fourth day.
Table (4): Predation rates for final instar E. scitula larvae feeding on
C. rusci at three different conditions.
period
1st day
2nd day
3rd day
4th day
Mean
26 ˚C ± 0.5, (65± 2
RH.) n = 30
220 (73.7%)
262 (87.3%)
278 (92.7%)
244 (81.3%)
251 (83.75%)
28˚C ± 0.5 , (70 ±
2 RH.) n =30
232 (77.3%)
266 (88.7%)
291 (97 %)
250 (83.3%)
259.75(86.6%)
30˚ C ± 0.5, (75 ±
2 RH.) n 30
256 (85.3%)
282 (94 %)
288 (96 %)
252 (84 %)
269.5 (89.8%)
N.B: Data are shown in parentheses represented corrected mortality by Abbott's
formula
Discussion
Infestations of C.rusci on fig and other ornamental plants were
considered of economic significance in the different countries around
the world. essential. Some natural enemies (Pharoscymnus ovoides
(Sicard), Cydonia vicinaisis Cr. and Eublemma scitula (Ramb.) have
all been used in classical and augmentative biocontrol programs for
control of Homoptera, including C. rusci (Argyriou & Mourikis 1981;
Waterhouse & Sands 2001 and Nga et.al 2006). Importantly, E.
scitula is itself the most dominant species of economic significance
because attacks several other target species (Table 2), it may be
effective at controlling those species as well. Alternatively, E. scitula
may bred on these substitute hosts if C. rusci numbers are small prior
to the peak activity time determined for optimal release. This
strategy has been used in Derna, where control agents for
Planococcus citri (Risso) were bred during the rainy season on P.
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lilacinus and liberated against P. citri at the beginning of the dry
season (DeBach & Hagen 1970 and Nga et.al. 2006).
The biological data for C. rusci and E. scitula recorded here are an
important first step in planning an augmentative biocontrol
program. Results from this experiment suggest that E. scitula may
indeed be a useful biological control agent for C.rusci in Derna.
However, some apparent breeding problems need to be addressed
before more trails can proceed. First, it is important to determine the
optimal environmental conditions for breeding E. scitula in captivity
and confirm that the high attrition rate in first instar larvae is not an
artifact of the laboratory environment. During the course of the
predation experiments with E.scitula and the C. rusci, first instar E.
scitula larvae were very active and often crawled incessantly for an
hour or more without consuming any prey. It is not known if this was
due to less than optimal environmental conditions in the laboratory,
but the behavior almost certainly contributed to the low survival rate
of E. scitula. This hyperactivity in first instar E.scitula larvae may be
a survival strategy to optimize the chances of encountering suitable
prey. The tactic could be useful when prey populations have a patchy
distribution, or when excessive numbers of predators feeding on a
limited resource could result in none of predators surviving. Even
though the wandering behavior may result in a high attrition rate in
first instar E. scitula larvae, the overall survival rate of species may
be enhanced. If this high attrition rate of first E.scitula larvae is
normal in the field, then large numbers of eggs may need to be
harvested for release. Conversely, because first instar larvae are very
highly mobile, it may only be necessary to introduce E. scitula eggs to
different parts of fig trees and allow them to locate C. rusci infestion.
This could simplify the process of introducing E. scitula to fig
orchards and would clearly be beneficial to farmers. More field trials
will need to be undertaken to determine if highly mobile larvae can
locate and attack C. rusci infestation wherever they are located on a
tree.
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