INSECTICIDE RESISTANCE AND RESISTANCE MANAGEMENT Using a Generational Time-Step Model to Simulate Dynamics of Adaptation to Transgenic Corn and Crop Rotation by Western Corn Rootworm (Coleoptera: Chrysomelidae)

We expanded a simulation model of the population dynamics and genetics of the western corn rootworm for a landscape of corn, soybean, and other crops to study the simultaneous development of resistance to both crop rotation and transgenic corn. Transgenic corn effective against corn rootwormwas recently approved in 2003 andmay be a very effective new technology for control ofwesterncorn rootworm inareaswithorwithout the rotation-resistant variant. In simulationsof areas with rotation-resistant populations, planting transgenic corn to only rotated cornÞelds was a robust strategy to prevent resistance to both traits. In these areas, planting transgenic corn to only continuous Þelds was not an effective strategy for preventing adaptation to crop rotation or transgenic corn. In areas without rotation-resistant phenotypes, gene expression of the allele for resistance to transgenic corn was the most important factor affecting the development of resistance to transgenic corn. If the allele for resistance to transgenic corn is recessive, resistance can be delayed longer than 15 yr, but if the resistant allele isdominant thenresistanceusuallydevelopedwithin15yr. Ina sensitivity analysis, among theparameters investigated, initial allele frequencyanddensitydependencewere the twomost important factors affecting the evolution of resistance. We compared the results of this simulation model with a more complicated model and results between the two were similar. This indicates that results froma simplermodelwith agenerational time-stepcancompare favorablywith amorecomplex model with a daily time-step.