Laboratory Evaluation of three Bacillus thuringiensis Berliner - based Biopesticides against the Diamondback moth Plutella Xylostella (Linnaeus)

Three commercially available Bt-based biopesticides, viz., Dipel 8L Biolep, Halt, were evaluated in bioassay studies against third instar larvae of Plutella xylostella (Linnaeus). The LC₅₀ values for the three products calculated by using PCAT software package MSTAT were 0.013, 0.039 and 0.22 per cent, respectively. The slope values for the probit-regression equation were 1.28, 1.49 and 1.43 for Dipel 8L, Biolep and Halt, respectively. Dipel 8L found most promising in the bioassay studies, was used for further studies on food consumption and indices of growth of P. xylostella larvae as affected by feeding on Bt-treated food. There was a concentration dependent decrease in the amount of food consumed by the surviving larvae. The indices of growth like CI, AD, EC1 and RGR of such larvae were also adversely affected.