Dynamics of insect resistance in Bt-corn

The development of genetically modified Bt-corn, incorporating various toxin genes from Bacillus thuringiensis that act as a chemical defense against insect pests, such as the European Corn Borer, provides farmers with a new pest management option. However, the emergence of insect resistance is a threat to the continued use of Bt-corn. The United States Environment Protection Agency (US EPA) has developed planting strategies, for preventing insect resistance by planting a mixture of Bt- and non-Bt-corn. Decisions about the exact proportion of Bt- and non-Bt-corn are based on complex spatially explicit mathematical models using detailed biological assumptions about the population genetics and life history of the European Corn Borer. We develop an alternative simpler model for the spread of resistance based on the logistic growth model, which we believe has utility in situations where it is impossible or impractical to estimate the different life history and genetics parameters required by more detailed models. We use our model to investigate the US EPA’s planting rules for Bt-corn and find that short-term economic behavior is likely to lead to these rules not being followed. Our results add weight to existing work on this problem. We also investigate the economics of planting Bt-corn in markets where consumers do and do not differentiate between the modes of production for the corn. We find that Bt-corn appears to be economic in markets that do not differentiate and uneconomic in markets where consumers do differentiate.