The population dynamics and population genetics of two bivoltine species of corn borers are modeled in a hypothetical region of irrigated transgenic and nontransgenic corn. European corn borer, Ostrinia nubilalis (Hübner), adults were assumed to disperse throughout the landscape for both mating and oviposition. Southwestern corn borer, Diatraea grandiosella Dyar, adults were assumed to have very localized dispersal behaviors. Resistance developed quickly in both species when the allele for resistance to the transgenic toxin was dominant. When the allele for resistance was not dominant and few or none of the heterozygous larvae survived the toxin, the behaviors of adult insects determined the speed of resistance development. With block refuges of 10–40% the European corn borer developed resistance within 15–38 yr, but the southwestern corn borer never developed resistance within the 100 yr simulated. A row-strip refuge configuration did not change the time for resistance to develop in the European corn borer; however, row-strip refuges cannot be recommended for the southwestern corn borer. Uncertainty about adult behaviors in irrigated corn led us to examine the potential impact of behavior on resistance development. Adult behaviors influenced resistance development more than refuge size. For instance, if the first flight of moths exhibit random mating and uniform oviposition throughout the landscape and the second flight exhibits localized mating and oviposition, resistance developed at least five times faster in the southwestern corn borer population and three times slower in the European corn borer population compared with our standard assumptions. We discuss the implications of adult behavior, refuge configuration, refuge placement within the landscape and year-to-year relocation on resistance management plans.