GENERAL INTRODUCTION
The economy of India mainly depends on agriculture and it provides livelihood to many
people. Agriculture plays an important role in our life, so agricultural crop productions
should be increased and it must be protected from the pest attack. About 14 percent of all
crops are lost due to insect pests, resulting in economic losses estimated at $ 200 billion
per year in United States and $2 trillion worldwide (Pimental, 2009). In India the reported
annual loss due to insect pest is around Rs. 8, 63,884 million (Dhaliwal et al., 2010).
Insect pest also have devastating effects on human health due to disease transmitting
insect vectors such as mosquitoes, biting flies, chiggers, fleas and ticks that spread
infections to hundreds of millions of people each year. There are several insect pests
which cause severe losses in different field crops, including Helicoverpa armigera on
pulses, cotton, vegetables and sunflower, Plutella xylostella and Spodoptera litura on
vegatables, wooly aphids (Ceratovacuna lanigera) on sugarcane. H. armigera (Hubner)
(Lepidoptera : Noctuidae ) is one of the important pest as it has a host range more than
300 host plants including cotton legume sunflower, wheat, groundnut, tomato, tobacco,
corn and a range of vegetables, fruit crops and tree species (Fitt, 1989; Rajapkshe and
Wallter, 2007).
Different species from the genera Heliothis/Helicoverpa complex (Helicoverpa
armigera, Heliothis zea.Heliothis virescens exique and Heliothis punctigera) feed on a
wide range of hosts (Fitt, 2000; King, 1994; Metthews. 1999). The legume pod borer or
cotton bollworm (Helicoverpa armigera Hübner) is a major constraint to crop production
globally. It is one of the most important insect pests in the world due to its mobility, high
polyphagy, short life cycle and high reproductive rate (Lawo et al., 2008). Beside, the
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ability of ovipositing females to locate and utilize a wide range of hosts from a number of
families is one of the major factors contributing to the pest status of this moth (Fitt, 1989;
Zalucki et al., 1986). H. amigera larvae are extremely destructive, because they prefer to
feed and develop on the reproductive structures of crops which are rich in nitrogen (Fitt
1989). These structures are often the part of the crop that is harvested (King 1994).
Depending on the crop, bollworm induced damage can range from 50 to 90 percent of the
yield (Reed and Pawar 1982, Sehgal and Ujagir 1990). H. amigera is extremely well
adapted to agroecosystems and can exhibit up to 11 generations a year under good
conditions (Shanower and Romeis 1999). The bollworm has evolved 2 major strategies
for adapting to adverse conditions. First, it has excellent migratory abilities and can fly up
to 155 miles (250 km) in search of a viable food source (McCaffery et al. 1989).
Secondly, it has the ability to enter into facultative diapauses when conditions become
too hot or cold (King 1994). This allows the bollworm to survive until environmental
conditions improve. A conservative estimate suggest that over US $1 billion was spent on
insecticides to control this pest and H. armigera has developed a high level of resistance
to many of the commonly used pesticides. (Kranti et al., 2002).
Management of Helicoverpa armigera:
Helicoverpa armigera is active from July-October and February-April. The adult moth
is stout, yellowish brown with a dark speck area on the forewings, which have grayish
wavy lines and a black kidney shaped mark whereas the hind wings are whitish with
blackish patch along the outer margin. The larva is about 35 mm long, greenish brown
with dark gray yellow stripes along the sides of the body. The larvae feed on the leaves
7
initially and then bore in to the square/bolls and seeds with its head push into the boll,
leaving the rest of the body outside.
For the management of insect pests, a number of strategies are employed which include
physical/ mechanical control, culture control, chemical control and biological control. For
H. armigera management, these strategies have been used individually or in combination
so as to maintain its population below economic threshold level (ETL’s) as determined by
the relationship between population density and economic loss.
Mechanical and cultural control: Mechanical control is the oldest method. It includes
measures like collection of egg masses and other inactive stages, removal of infested
parts or whole plants trenching, application of dry heat including exposure to sun rays
during hot months to reduce infestations by insects. This method is useful during the
initial stages of pest incidence and when practiced as a concerted efforts by a large
number of farmers in a particular area.
A number of cultural practices are followed so as to develop practical strategies to reduce
the impact of H. armigera on different crops. The most common practices involve the use
of short duration varieties, adjusting the time of sowing to avoid peak pest incidence, use
of companion crops, trap crops etc. Other culture practices include deep ploughing after
harvesting the crop and plant spacing.
Chemical control: Chemical pesticides still remains the most effective practice to
manage Helicoverpa especially on high value crop such as cotton and vegetables.
Significant reduction in larval population of H. armigera was observed by spraying insect
growth inhibitors such as diflubenzuron (Ahmed et al., 2003). Despite the advantages of
8
effectiveness, convenience, simplicity and flexibility, the indiscriminate use of chemical
pesticides has resulted in the development of resistance in insects to insecticides,
resurgence of pests, outbreak of secondary insect pest species, destruction of natural
enemies and accumulation of pesticides residues in food above the tolerance limits
besides pollution of the environment.
In India over 700 species of insect pests have developed resistance to both individual
chemical insecticides as well as to group of chemicals, a notable example being H.
armigera, which has attained the status of ‘national pest’ (Bergvinson, 2005). Resistance
has been reported in H. armigera to endosulfan, profenphos, thiodicarb, alphacypermethrin, deeltamenthrin lambdacycalothrin, bifentrin and cyfluthrin (Ahmed et al.,
2004; Kranti et al., 2001).
It is conceded that the use of pesticides is not satisfactory solution to the pest problem
and increasing resistance of Helicoverpa to existing chemical insecticides has also
increased the cost of control and potentially lower profits for chemical companies and
farmers (McCaffery, 1998). Indiscriminate use of pesticides for control of H. armigera
has resulted in the development of resistant against almost all groups of conventional
insecticides, environmental pollution, and loss of predators, parasites and health hazards.
There is a need of strategies to reduce the dependency on pesticides to ensure the
sustainability of crop production. Therefore, it becomes imperative to search for
alternative methods which are ecologically sound, reliable, economical and sustainable.
So in past decades, unreasoned or systematic (calendar spraying) chemical control has
been progressively replaced by integrated pest management (IPM) programmers in India
(Fitt, 2000a & 2000b).
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Integrated pest management (IPM): IPM is a utilization of all suitable techniques and
methods in a compatible manner as possible and suppresses pest populations below the
economic injury level (EIL). Integrated pest management is always considered to be
economical, effective, practical and protective. It attempts to ensure biological balance in
the nature besides increasing the cost-benefit ratio by minimizing expenditure on
pesticides and their application. The major tools for the development and practice of IPM
strategy are pest surveillance, mechanical and physical methods, culture methods
biological methods and chemical methods (Motshwari Obopile, 2008).
Biological control: Biological control is a major component of integrated pest
management which has a maximum contribution of naturally occurring parasitoids,
predators, and pathogens have great potential as biological control agents of insect pests
(Gopali and Lingappa, 2001; Jones et.al., 2004; Kaur, 2006). In recent years, however,
several studies have shown that some bio- logical control agents have deleterious effects
on pests. (Simberloff and Stiling 1996, Follet and Duan 2000, Strong and Pemberton
2000a, b). Biological control involves large scale multiplication and liberation of such
agents, or creating conditions under which naturally occurring biocontrol agents can act
effectively and this method has long been considered an environmentally benign
approach to controlling invasive pests ( Elkinton et.al,. 2006). It is alternative method to
chemical control and practically more effective. It is an artificial modification of natural
biological phenomenon for reducing or checking destructive population of insect pests. It
typically involves an active human role. Natural enemies of insect pests also known as
biological control agents are categorised as parasitoids, predators and pathogens.
Predators are mainly free-living species that consume a large number of preys during
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their lifetime. Pathogens are microorganisms including certain bacteria, fungi, nematodes,
protozoa, and viruses that can infect and kill the host (Roome, 1975).
Biological control is an important component in H. armigera management and plays a
vital role in sustainable crop production. The research on biological control of H.
armigera received considerable impetus by the establishment of the Project Directorate of
Biological Control in India. About 120 species of biological control agents have been
recognized to be associated with H. armigera (Singh, 2012).
In the present studies the use of insect parasitoids in controlling the pest’s population has
been given the priority. Parasitoids are usually described according to the life stage of the
host that they attack, Ex. The tiny Trichogramma wasp is called an egg parasitoid
because it attacks the egg stage. Campoletis chlorideae (Uchida) parasitite are called
larval parasitoids because they attack the larval stage. Chalcid is pupal parasitoid because
it attacks pupal stage (Van Hamburg and Guest, 1997).
Insect Parasitoid is an organism that lives and feeds in or on a larger host. Insect parasites
(more precisely called parasitoids) are smaller than their host and develop inside, or
attach to the outside, of the host’s body. Often only the immature stage of the parasite
feeds on the host, and it kills only one host individual during its development. There are
104 Parasitoids from Diptera and Hymenoptera in which 12 are egg parasitoids, 88 are
Larval and 10 are pupal parasitoid. From Hymenoptera - 26 Ichneumonidae, 30
Brachonidae, 26 Tachinidae, 2 Nematodes and 3 pupal parasitoids have been reported as
effective parasitoids of Helicoverpa armigera (Hubner).
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As part of an overall Integrated Pest Management (IPM) program, biological control
methods can reduce the legal, environmental (soil, air, and water pollution), and health
hazards. Unlike most insecticides, biological control is often very specific for a particular
pest. People, animals, or beneficial insects may be completely unaffected or undisturbed
by their use. There is also less danger to the environment and water quality. It does not
intensify or create new pest problems; the beneficial insects are already available. The
pest is unable (or very slow) to develop a resistance and Control is self perpetuating.
More than 32 million hectors of agriculture and forestry are being treated annually with
parasitoids to control insect pests (Li, 1994).
Hence the biocontrol method is cost effective, safe and cheap so it invited the attention of
scientist with better insight into the study of pests. Biocontrol is important subject of
entomologist’s pest management programmes because of the spectacular success that
have been achieved in the past and still there is a need of use of parasitoids.
Use of Parasitoids Hymenoptera and Diptera from major groups of insects are very
useful. So these beneficial flies have importance in integrated pest management. The
present investigation on the utilization of biocontrolling agents on pest like H. armigera
has been carried out. Hymenoptera constitute one of the largest and most successful
orders of insects. In recent years interest in the parasitoid Hymenoptera has grown as a
result of the increasing demand for biological methods for pest control and their possible
use as natural enemies. The Braconidae are the second largest family of this order, the
majority of species are primary parasitoids of immature stages of Lepidoptera, Coleoptera
and Diptera (Sharkey 1993, Thanavendan 2010).
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In present work, we have used Chelonus blackburni Cameron (Braconidae:
Hymenoptera) and Trichogramma brasiliensis Ashmead which are are egg- larval and
egg parasitoid of H. armigera respectively. C.blackburni one of the dominant and bodily
stout exotic parasitoid accepting parasitisation in certain lepidopteran range. It is an egglarval, endoparasitic and uniparental parasitoid introduced from Hawai, USA, and now
fairly widely established in different parts of India (Raj et.al., 1999; Jackson et al.1978;
G. Thanavanedan and S. Jayarani, 2009). The potential of C.blackburni has been
evaluated against few lepidopteran pests by earlier research workers from parasitisation
as well as efficiency point view. Use of C. blackburni gave good control of H. armigera
(Pawar and Prasad, 1985).
The true T. brasiliensis was used as a biocontrolling agent to control the population of H.
Armigera.The eco-biological aspects of T. Brasiliensis were studied in relation to
different range of temperatures on H. armigera eggs at laboratory conditions 10 to 40 °C.
Life cycle of C. blackburni on H. armigera:
C. blackburni oviposits its eggs in H. armigera eggs and complete development in the
host larva. Upon detecting a host egg, Chelonus adult antennates with the tips of antenna
several times before she oviposits. If the host egg is acceptable oviposition lasts 20-40
seconds.
Larvae of Chelonus shows three different instars first and second instars are
endoparasitic but 3rd instar is endoparasitic in early developmental stage and
ectoparasitic later. Endoparasitic stage feed primarily on hemolymph. Last instar cut out
13
of the thoracic region of the host larva and emerges. The parasitoid larva then bends
around and devours its host, beginning at the posterior end. The last few abdominal
segments of the parasitoid remain in the host until this feeding is complete. The parasitoid
consumes the entire host except for the head capsule and body cuticle. After it devour its
host, the parasitsoid spins its cocoon an pupate in the cocoon of the host, where it remains
for 6-7 days, after the cocoon was completed, the parasitoid became a pre-pupa and
discharge meconium just prior to pupation. The adults emerged through a ragged hole cut
in the anterior part of the cocoon. The larva of H. armigera fails to pupate and will die.
The parasitoid develops from an egg to an adult in around 28 days in H. armigera.
Figure 1. Life cycle of the herbivore Helicoverpa armigera and the parasitoid Chelonus
blackburni that parasitize eggs of the herbivore.
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In present work, we focused on mass production of C. blackburni on different host.
Quality of C. blackburni as parasitoids for the potential biocontrol of H. armigera by
measuring the relative reduction in food consumption and weight gain through larval
development. Our specific goals were to quantify how much parasitized larvae eat and
gain weight in comparison to unparasitized. Host parasitoid interactions in C. blackburni
and H. armigera the effect of parasitization on haemocytes population were studied.
Histological work was carried out to study the effect of parasitization on midgut tissues
of H. armigera. Studied the characterization of different types of sensilla present on the
antennae of C. blackburnii based on their external morphology which are used in guiding
an insect to its host.
The major objectives of the present studies are:
¾ Mass production of host insects Phthorimaea opercuella (Zeller) and
Corcyra cephalonica Stanton for the rearing of parasitoid C. blackburni
Cameron.
¾ Influence of C. blackburni, on the growth and food consumption of host
H. armigera.
¾ Haemocyte types and total and differential count in unparasitized and
parasitized H. armigera larva.
¾ Histological study of H. armigera midgut parasitized by C. blackburni
Cameron.
¾ Antennal sensilla of hymenopteran parasitoid C. blackburni Cameron
¾ Tritrophic interaction between Cicer arietinum, H. armigera and
blackburni
15
C.
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