Response of Laboratory and Field Populations of Cotton Boll Worm, Helicoverpa armigera to Bt Cotton

Variation in susceptibility of Helicoverpa armigera Hub from laboratory and field populations to three Bt cotton hybrids was studied. Mean mortality of field collected H. armigera neonates to top leaves of MECH 162. MECH 184 and RCH 2 were 90.0, 91.7 and 90.0 per cent, respectively. The order of susceptibility of different larval instars to Bt cotton hybrids were neonates > second instar > third instar. The efficacy of different plant parts was in the order of top leaves > middle leaves > squares > bolls. Among the Bt hybrids, MECH 184 was highly effective followed by MECH 162 and RCH 2.