Parasitic Potential of some Braconid Parasitoids against Okra Fruit Borers

Abstract

In surveys conducted in Coimbatore district during 2009-10, Okra fruit borers, Earias vittella Fabricius, Earias insulana Boisdual and Helicoverpa armigera (Hübner) were the serious pests causing 50 per cent loss. During the survey, three hymenopteran parasitiods viz., Bassus spp., Brachymeria lasus Walker, Goryphus spp., of the families Braconidae, Chalcididae and Ichneumonidae against Earias spp. and the dipteran parasitoid, Carcelia illota (Tachinidae ) against H. armigera were recorded with 0.00 to 10.00 per cent parasitization. All the parasitoids recorded were not amenable for mass culturing, and hence, other braconid parasitoids viz., Bracon brevicornis Wesmael, Bracon hebetor Say and Chelonus blackburni Cameron were studied for their parasitic potential against fruit borer complex. Cent per cent parasitization was observed with B. brevicornis against all instars of E. vittella and H. armigera, higher parasitizaion of 100 and 97.50 per cent was observed by B. hebetor at a parasitoid-host ratio of 5:10 on second instar larvae of H. armigera and fourth instar larvae of E. vittella respectively. The egg - larval parasitoid, C. blackburni recorded the highest parasitization of 70.54 per cent and 64.58 per cent against E. vittella and H. armigera at a parasitoid host ratio of 5:100. For B. brevicornis and B. hebetor, highest cocoon formation and parasitoid emergence was recorded at 4:10 ratio against third and fourth instars. In C. blackburni, the parasitoid host ratio of 3:100 yielded the highest number of adult parasitoids. B. brevicornis was found to be more effective against fruit borers.