Methods of rearing, infestation and evaluation for Chilo partellus resistance in sorghum

The parasitic wasp, Campoletis chlorideae is an important larval parasitoid of Helicoverpa armigera a serious pest of cotton, grain legumes and cereals. Large-scale deployment of Bt-transgenic crops with resistance to H. armigera may have potential consequences for the development and survival of C. chlorideae. Therefore, we studied the tritrophic interactions of C. chlorideae involving eight insect host species and six host crops under laboratory conditions. The recovery of H. armigera larvae following release was greater on pigeonpea and chickpea when compared with cotton, groundnut and pearl millet. The parasitism by C. chlorideae females was least with reduction in cocoon formation and adult emergence on H. armigera larvae released on chickpea. Host insects also had significant effect on the development and survival of C. chlorideae. The larval period of C. chlorideae was prolonged by 2-3 days on Spodoptera exigua, Mythimna separata and Achaea janata when compared with H. armigera, Helicoverpa assulta and Spodoptera litura. Maximum cocoon formation and adult emergence were recorded on H. armigera (82.4% and 70.5%, respectively) than on other insect hosts. These studies have important implications on development and survival of C. chlorideae on alternate insect hosts on non-transgenic crop plants, when there is paucity of H. armigera larvae on transgenic crops expressing Bt-toxins.