Development time and resistance to Bt crops

Crop plants genetically engineered to produce insecticidal toxins derived from the bacterium Bacillus thuringiensis (Bt) are being grown on millions of hectares, but their success will be short-lived if pests adapt to them quickly1,2. The primary strategy for delaying insect resistance to transgenic Bt plants is to provide refuges of host plants that do not produce Bt toxins. This potentially delays the development of insect resistance to Bt crops by providing susceptible insects for mating with resistant insects. But our laboratory results with a worldwide pest of cotton, pink bollworm moths (Pectinophora gossypiella)3, contradict an important assumption of the refuge strategy. We find that a resistant strain of larvae on Bt cotton takes longer to develop than susceptible larvae on non-Bt cotton. This developmental asynchrony favours non-random mating that could reduce the expected benefits of the refuge strategy.