Transgenic Bt corn hybrids that produce insecticidal proteins from the soil bacterium Bacillus thuringiensis (Bt) have become the standard insect management tactic across the U.S. Corn Belt. In 2012, 67 percent of 96.4 million acres of corn planted in the U.S. contained a Bt trait (USDA ERS, 2012; USDA NASS, 2012). Widespread planting of Bt corn creates intense selection pressure for target insects to develop resistance. Evolution of resistance diminishes the efficacy and benefits of Bt corn technology.
Because Bt traits are pesticidal substances produced by plants, the U.S. Environmental Protection Agency (EPA) registers Bt crops through the Federal Insecticide Fungicide and Rodenticide Act (EPA, 2012). Recognizing the threat of evolution of insect resistance, the EPA requires registrants (seed companies) to include an insect resistance management (IRM) plan when applying to register a Bt crop. The goal of the IRM plan is to reduce selection pressure associated with Bt crops and prevent, or at least delay, development of resistance in the target insect population. Growers are required to implement the IRM plan on-farm by planting a refuge. The refuge provides a corn crop habitat that allows target pest insects to develop without exposure to the Bt trait. Mating between susceptible insects from the refuge and potential resistant insects from the Bt corn minimizes the chance of resistance developing in the population.