EPA has required insect resistance management (IRM) plans for Bt crops since 1995. Presently, the registered Bt crops include Bt cotton, Bt corn (Lepidopteran-protected), and Bt corn (Rootworm-protected). Bt crops are especially at risk for the development of resistance because of their sustained, season-long, dose expression of Bt toxin(s). The IRM requirements for each crop are based on the biology and ecology of the primary target pest(s), dose expression of the Bt crop, genetics of resistance, susceptibility of the pest to the toxin(s), mode of action of the Bt toxin(s), number of Bt toxins expressed in the crop, and selection intensity. The preferred IRM strategy for Bt crops has been a high dose and structured refuge approach (a portion of a grower's field is planted to non-Bt varieties). The IRM requirements include a: 1) structured refuge, 2) resistance monitoring program, 3) compliance assurance program, 4) grower education program, and 5) remedial action plan in the event of potential resistance.