Temporal and Spatial Variations in Susceptibility of Helicoverpa armigera (Hub.) From Different Agronomic Hosts to Bt Cotton

Refuge is widely recommended as a resistant management strategy in Bt cotton. As an alternative to refuge, the other host crops may be used. The susceptibility of H. armigera larvae collected from different agronomic hosts (bhendi, red gram, chickpea, tomato and cotton) to Bt cotton hybrids were studied. H. armigera larvae collected from different agronomic hosts were highly susceptible to Bt cotton hybrids at 60 DAS and the susceptibility decreases at 90 and 120 DAS. The toxicity of different plant parts of Bt cotton hybrids to the larvae from different agronomic hosts was in the order of top leaves > middle leaves > squares > bolls. H. armigera neonates from chickpea recorded maximum mortality to MECH 184 Bt at 60 DAS. Susceptibility of second and third instar H. armigera collected from different hosts to Bt cotton hybrids was in the order of chickpea > red gram > bhendi > tomato > cotton. The order of effectiveness of different Bt cotton hybrids to H. armigera collected from different hosts were MECH 184 Bt > MECH 162 Bt > RCH 2 Bt. The possibilities of these alternate host as a refuge to Bt cotton was discussed.