Rohit Singla
McGill University, Montreal
Phillip Johnson and Sukant Misra
Texas Tech University

Refuge requirements for Bt cotton varieties were examined for three cotton-growing regions in India, considering resistance evolution in cotton bollworm (Helicoverpa armigera) to Bt toxin and pyrethroid pesticides. Biological, yield, and regulatory models were used. Results indicated that the optimal refuge requirements varied significantly across cotton-growing regions. The North and Central regions require higher refuge compared to the South region. Results suggest that sprayed refuge is more profitable than unsprayed refuge. Refuge requirements were found to be sensitive to relative proportion of pests in natural refuge and initial Bt resistance levels in all three regions.

Key words: Bt technology, cotton bollworm, India, natural refuge, resistance, structured refuge.