United States Environmental Protection Agency Insect Resistance Management Programs for Plant-Incorporated Protectants and Use of Simulation Modeling

Widespread adoption of Bt crops and persistence of Bt toxins expressed in transgenic plants could cause rapid evolution of resistance in pests and lead to the loss of the intrinsic environmental and economic benefits associated with this technology and that of Bt microbial pesticides used in organic and conventional agriculture. The United States Environmental Protection Agency (EPA) requires insect resistance management (IRM) programs for plant-incorporated protectants (PIPs) that express insecticidal toxins from the soil bacterium Bacillus thuringiensis (Bt). The basis for this decision is that maintaining the susceptibility of agricultural pest insects to Bt is an important public resource. In contrast to the voluntary pesticide resistance management programs for conventional pesticides, the IRM programs for Bt PIPs are mandatory and are unprecedented in their detail, scope, and implementation. EPA has relied on both empirical data and mathematical simulation models to assess the evolution of resistance and evaluate IRM strategies. IRM requirements have changed over the past 15 years in conjunction with the development of new Bt PIP products and advances in our understanding of the biological, ecological, genetic, and operational factors that influence the evolution of insect resistance. This chapter focuses on the scientific framework EPA uses to assess and manage the risk of insect resistance to Bt PIPs with particular interest in the factors that influence resistance and the use of IRM models to evaluate different resistance management strategies.