Effects of Bt cotton and Cry1Ac toxin on survival and development of pink bollworm (Lepidoptera : Gelechiidae)

We evaluated the effects of Bacillus thuringiensis (Bt) toxin Cry1Ac on sur vival and development of a susceptible strain and laboratory-selected resis tant strains of pink bollworm, Pectinaphora gossypiella (Saunders). For sus ceptible and resistant strains tested on artificial diet, increases in Cry1 Ac concentration reduced developmental rate and pupal weight. In greenhouse tests, survival of resistant larvae on transgenic cotton that produces Cry 1Ac (Bt cotton) was 46% relative to their survival on non-Bt cotton. In con trast, Bt cotton killed all susceptible larvae tested. F, hybrid progeny of resistant and susceptible adults did not survive on Bt cotton, which indic ates recessive inheritance of resistance. Compared with resistant or suscep tible larvae reared on non-Bt cotton, resistant larvae reared on Bt cotton had lower survival and slower development, and achieved lower pupal weight and fecundity. Recessive resistance to Bt cotton is consistent with one of the basic assumptions of the refuge strategy for delaying resistance to Bt cotton. Whereas slower development of resistant insects on Bt cotton could increase the probability of mating between resistant adults and accelerate resistance, negative effects of Bt cotton on the survival and development o f resistant larvae could delay evolution of resistance.