I expanded the population dynamics and genetics model published in 2005 by Crowder and Onstad to include larval survival and movement to evaluate the role of mixtures of transgenic and nontransgenic corn, Zea mays L., seed for resistance management of western corn rootworm. I studied both density-independent and density-dependent toxin survival. In all but the worst-case scenarios, resistance did not evolve within 30 yr when the resistance allele, R, was recessive. The standard model with density-independent toxin survival based on the expression of a medium dose of toxin indicated that 50% R allele frequency will be reached by years 5 and 7, respectively, with dominant and partially recessive expression and 20% nontransgenic seed. The standard model with density-dependent toxin survival indicates that resistance will occur in year 5 under the same conditions. These results are similar to the published results of Crowder and Onstad who studied a model with adjacent block refuges and mostly nonrandom mating in the landscape (random only within each block). Results depended on the heterozygote advantage (differential survival between SS and RS) and the degree of random mating provided by the seed mixture.
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Vol. 99 • No. 4