author(s)
Vrushali Pawade, S. M. Thakare, B.S. Ghodaki

abstract
The bioassays on Helicoverpa armigera were conducted against leaves, squares, flowers and bolls from 15 to 135 days after emergence (DAE) on first, second and third instars of H. armigera, separately for two seasons during 2007-08 and 2008-09. Cent per cent mortality was observed in all Bt hybrids on first and second instar of H. armigera. However, in third instar larvae the average mortality was between 58.33 to 96.25 per cent. There was inverse relationship between amounts of Cry1Ac toxin in the plant parts versus the weight of larvae. Amongst Bt cotton hybrids Tulshi-9 recorded highest average mortality (80.00 to 96.25%) followed by RCH-Alto and JK-99 (75.00 to 92.50% and 71.67 to 90.00%, respectively) and lowest in Mallika and MECH-162 (both 58.33 to 80.00%). The non-Bt cotton hybrid PKV Hy-2 recorded lowest average per cent morality against first, second and third instars of H. armigera and all the Bt hybrids were found superior over non-Bt cotton hybrid.