In field trials since 1995, overspray programmes of Karate ( -cyhalothrin) on B.t. cotton have demonstrated excellent control of secondary pests and lepidopteran pests such as bollworm (Helicoverpa zea) that are capable of survival on the transgenic plants. Laboratory studies reported here clearly demonstrate that insects such as Heliothis virescens, Helicoverpa zea, Trichoplusia ni, and Spodoptera exigua are many times more sensitive to a subsequent Karate spray treatment when they have survived prior exposure to B.t. As well as the inherent yield benefits from this Karate overspray approach, the enhanced insecticidal activity enables a more practical resistance management strategy for B.t. cotton to be envisaged. Karate oversprays, in conjunction with proper refugia, will further reduce the likelihood of B.t. survivors and the development of resistance. This approach is probably the best practical resistance management strategy for B.t. cotton.