Effect of Bacillus thuringiensis Subspecies kurstaki and its Endotoxin Cry1Ab on Growth and Development of Helicoverpa armigera Hübner

Effect of Bacillus thuringiensis subspecies kurstaki and its principal endotoxin Cry1Ab on the growth and development of the American bollworm, Helicoverpa armigera Hiibner was studied under laboratory conditions using artificial diet incorporation method. Cry1Ab was about 16 fold less toxic than HD-1 endotoxin to the neonates of H armigera. Both preparations did not cause any mortality of 2^nd and 3^rd instar larvae, however, they inhibited growth and development at low concentrations. The EC₅₀ of Cry1Ab for inhibition of growth of larva over 7 d period was 0.93 ppm for 2^nd instar and 3.45 ppm for 3^rd instar. HD-1 showed EC₅₀ of 0.23 ppm for 3rd instar and was thus active than Cry1Ab.