Relative susceptibility OF Helicoverpa armigera (Hübner) and Spodoptera litura fabricius population to bollgard II cotton

Transgenic cotton, expressing Cry1Ac and Cry2Ab insecticidal δ-endotoxin protein of Bacillus thuringiensis Berliner often referred as Bt cotton, is widely grown in many countries. Bt cotton with a single cry1Ac gene and stacked also with cry2Ab gene provided satisfactory protection against major lepidopteran pests. A survey has been conducted in different cotton growing areas of Tamil Nadu to study the relative susceptibility of key lepidopteran pests viz., Helicoverpa armigera (Hübner) and Spodoptera litura Fab. to Bt cotton. Bioassay studies indicated that, H. armigera population collected from Madurai region recorded a maximum susceptibility of 96.67 per cent and Coimbatore population recorded a minimum susceptibility of 83.33 per cent to bollgard II (RCH 2 Bt). In the case of S. litura, the highest susceptibility was recorded from the population collected from Madurai region (70.00%) and lowest from Salem region (53.33).