When bollworm (Helicoverpa zea) attacks, cotton that is engineered to produce insecticidal toxins commonly called “Bt” (left) fends off the pest, while non-Bt cotton (right) is targeted and damaged. Pests such as H. zea can develop resistance to the toxins in Bt crops, however, and planting non-Bt crops nearby helps to slow evolutionary selection pressure that would lead to the development of resistance in the pest population. Planting such non-Bt “refuges” is an important, but underused, method for insecticide resistance management. (Photo credit: Dominic Reisig, Ph.D.)