Can refuge crops effectively manage resistance and population size in Colorado potato beetle?

Refuge crops may have contributed to the continuing effectiveness of transgenic insecticidal cultivars, but have not been widely used as part of resistance management for conventional insecticides. Much of the theory used to design refuge requirements was based on a lepidopteran life cycle and populations that are initially very susceptible to the high dose insecticide. In many lepidopteran pests, only the larvae are folivorous, and so selection acts only on the larvae in most models of resistance evolution. This study examines the potential for refuge crops to be effective population and resistance management tools for Colorado potato beetle, Leptinotarsa decemlineata, being treated with conventional insecticides, particularly neonicotinoid insecticides. In this model selection takes place among both larvae and adults, with resistance ratios and other parameters drawn from recent examples of resistance evolution to neonicotinoid insecticides. Resistance to neonicotinoids appears to be polygenic, and entails significant costs, in potato beetles. Cross resistance to earlier treatments, polygenic inheritance, and delays in implementing crop refuges will lead to within-population variation at the higher ends of resistance, rather than the highly resistant and highly susceptible single locus alleles in earlier models. The effectiveness of a treated or untreated refuge with adult as well as larval selection, costs of resistance, and polygenic inheritance will be modeled under varying conditions of resistance cost and dominance, refuge size, and distance from treated fields.