Economic analysis of transgenic maize and nontransgenic refuges for managing European corn borer (Lepidoptera: Pyralidae)

We simulated the population dynamics and population genetics of Europe;ln corn borer, Ostrinia nubilalis (Hubner), and damage to maize in a hypothetical region containing transgenic and nontransgenic maize and no other crops. The model assumes that the same level of refuge for resistance management is used every year over 15-20 yr and that no European corn borers immigrate into the region over the same period. When complete mixing across blocks between generations is assumed, the transgenic block significantly lowers damage to maize in the refuges. For most scenarios without toxin-titer decline during maize senescence, a 20% refuge is a robust, economical choice based on current value. At extremes of initial pest density or crop value (price X expected yield), refuge levels as low as 8% or as high as 26% can be superior. Nontransgenic maize can be planted as strips (at least 6 rows per strip) within a field or as separate but adjacent blocks to be effective at delaying resistance and providing economic returns at a 20% refuge level. With toxin-titer decline during senescence, the model results are sensitive to several biological parameters and assumptions with a 10% refuge level offering a robust, economic choice.