Discussion

Discussion

 Tachinidae is the largest family of parasitic Diptera and forms a major source of natural enemies for exploiting the biological control of Helicoverpa spp. Out of 30 tachinids reported from India on H.armigera, the significant species are Drino (Posturmia) imberbis Wiedmann, C.illota, and G.halli with 12-18%, 4-16%, and 18-20% parasitism by H.armigera (Achan et al., 1968). The exotic species Exorista bryani in release trials on pigeonpea and chickpea resulted 14.2% and 4% parasitism, respectively. Bilapate, 1981 reported 20% and 52% parasitism by G.halli and C.illota on cotton and sorghum, respectively in Parbhani - Maharashtra. Chaudhari and Nikam (1999) recorded 15.95% and 52% parasitism on chickpea and pigeonpea for C.illota on H.armigera, respectively in Rahuri - Maharashtra. C.illota and Exorista xanthospis provided 24.54% parasitism on sunflower (Patel and Talathi 1987) in Gujarat. Bhatnagar et al., (1982, 1983) reported 22% parasitism by tachinids on pigeonpea. This data is quite promising indicating bright future in control of H.armigera on pigeonpea, sorghum, sunflower, cotton and tomato crops in insecticide free area.

C.illota, Eucelatoria bryani, Goniopthalmus halli, Vora ruralis are common in India and America (Kogan et al., 1989). C.illota, Exorista sorbillans, Exorista xanthospis, G.halli, Plexorista imberbis, and P.laxa are common in India and Africa on cotton (Greathead and Girling, 1989). C.illota is common in India and Australia (Michael, 1989).

 Tachinidae like other hymenopterous parasitoid is not attempted for field release experiments except very few. Identification and rearing is the main problem with tachinidae. It is essential to study their comparative bioecology, release trials, breeding techniques, taxonomy, parasitoid complex because hymenopteros parasitoid are not effective for all crops particularly chickpea and pigeonpea as these exudes acidic secretions and the life stages of host which escape from hymenopterous attack are preferred by tachinids which further stops the life cycle of host. Early instars were mostly parasitoised by Hymenopteran parasitoids like C. chlorideae (11.87%), whereas late instars were parasitoised by Dipteran parasitoids like Carcelia sp. (10%) (Dayakar and Ray, 1999).

Lack of identification capability for taxa in tachinidae is a serious problem. The large numbers of species and poorly defined generic limits are the major obstacles to research in studies of the basic systematic of the family (Knutson, 1989).