Survival and Development of American Bollworm, Helicoverpa armigera on Bt Cotton Hybrids of Different Bt Events

Bt hybrids of different events were evaluated for their efficacy against the target lepidopteran through laboratory studies. The mortality of early larval instars of Helicoverpa armigera (Hubner) fed on leaves and squares of all the Bt event hybrids was higher than the later instars. Exposure of later instar larvae to plant parts of Bt event hybrids exhibited adverse effects on the growth and development such as reduced larval weights, prolonged larval developmental period, reduced pupation, formation of small pupae with less weight, reduction in adult emergence with low growth and survival indices for H. armigera. The growth index values were low for the larvae reared on leaves compared to those reared on squares of Bt cotton hybrids. The highest Cry protein toxin was observed at 60 DAS with a progressive decrease at 90 DAS and 120 DAS and negligible levels at 150 DAS during both the seasons. The Cry protein content was slightly high in RCH 2 BG-II hybrid compared to all the other Bt cotton hybrids.