Impact of parasitoids on Helicoverpa

Impact of parasitoids on Helicoverpa species:

             Three stages namely, eggs, larvae & pupae of Helicoverpa species are invaded by parasitoids, in addition to pathogens & predators.  In India, near about 162 arthropod parasitoids   have been recorded on H. armigera.  Among the three life stages of the pest H.armigera, larval stage is preferred by largest number of parasitoids (110) followed by egg (19), larval-pupal (13), pupal (12) & egg-larval (8) (Lingappa et al., 2001).  Of the recorded number of parasitoids (114) - Hymenoptera (82) & Diptera (30) nematoda (02) on H. armigera; 20 – Diptera (6), Hymenoptera (13), Nematoda (1) on H. Peltigera; and 19 – Diptera (04), Hymenoptera (14), Nematoda (01) on H.assulata were recorded. These natural enemies suppress the population of Helicoverpa species by destroying their immature forms.

In India, very few workers studied the biology, breeding methods & the impact of dipterous parasitoids on Helicoverpa species in comparison with hymenopterous parasitoids.  The trichogrammatids (11), Scelionidae (02) are the main egg parasitoids (Manjunath et al., 1970, Manjunath, 1972; Mani & Krishnamoorthy, 1983; Lingappa, 2001;Singh et al., 2002). The tachinids 30, bethylids (02), braconids (31) & ichneumonids (33) are the larval parasitoids, of which some are active on all the crops (Achan et al., 1968; Rao, 1968; Anonymous, 1974; Pawar et al., 1986 a, b).  Chalcids (02) & some tachinids (07) are the larval-pupal parasitoids. Few are egg – larval parasitoids. International Crops Research Institute for the Semi Arid Tropics (ICRISAT) has identified 27 species of parasites from Andhra Pradesh, Maharashtra and Karnataka states (Bhatnagar et al., 1982). Ten of these species are relatively effective in controlling the Helicoverpa populations. Dipterous parasitoids invade mainly on old larvae 3-6 instars, while hymenopterans prefer younger larvae (1-3 instars). Host plants also play important role in selection of host by their parasitoids.  Acidic exudates on chickpea & pigeonpea plants affect the parasitism mainly for hymenopterous egg parasitoids.