Fitness costs of resistance to cry1ac toxin in Helicoverpa armigera (Hübner)

Transgenic cotton producing a Bacillus thuringiensis is widely used for controlling Helicoverpa armigera (Hubner). Increasing adoption of Bt cotton expressing cry genes from Bacillus thuringiensis run under high risk for development of resistance. Fitness costs can greatly influence the rate of resistance evolution and also aids in delaying resistance. In the present study fitness costs in resistant H. armigera were evaluated by comparing biological performance to susceptible insects when reared on untreated diet. Parameters monitored includes larval survival, larval and pupal weights, pupal malformation, developmental time (larval and pupal) and reproductive traits (fecundity and fertility). From the results, it was found that fitness costs reduced survival of resistant strain on untreated diet by 12–25%. Significant weight differences were recorded between resistant and susceptible on untreated diet. Slower growth and development of resistant insects on untreated diet was also observed. Resistant insects took 2–4 days more for larval development, which led to emergence asynchrony between susceptible and resistant adults.