To slow evolution of western corn rootworm (Diabrotica virgifera virgifera LeConte) resistance to Bt (Bacillus thuringiensis Berliner) corn hybrids, non-Bt "refuges" must be planted within or adjacent to Bt cornfields, allowing susceptible insects to develop without exposure to Bt toxins. Bt-susceptible adults from refuges are expected to find and mate with resistant adults that have emerged from Bt corn, reducing the likelihood that Bt-resistant offspring are produced. The spatial and temporal distribution of adults in four refuge treatments (20, 5, and 0% structured refuges and 5% seed blend) and adjacent soybean fields was compared from 2010 to 2012. Adult emergence (adults/trap/day) from refuge corn in structured refuge treatments was greater than that from Bt corn, except during the post-pollination period of corn phenology when emergence from refuge and Bt plants was often the same. Abundance of free-moving adults was greatest in and near refuge rows in structured refuge treatments during vegetative and pollination periods. By post-pollination, adult abundance became evenly distributed. In contrast, adult abundance in 5% seed blends and 0% refuges was evenly distributed, or nearly so, across plots throughout the season. The persistent concentration of adults in refuge rows suggests that structured refuge configurations may not facilitate the expected mixing of adults from refuge and Bt corn. Seed blends produce uniform distributions of adults across the field that may facilitate mating between Bt and refuge adults and ultimately delay the evolution of Bt resistance.

To delay evolution of insect resistance to insecticidal Bacillus thuringiensis Berliner (Bt) transgenic crops, USA and Canadian maize growers commonly set aside a portion of each field as a refuge, where susceptible pests can develop without exposure to the toxin(s) expressed in the insecticidal crop. Abundant mate-seeking refuge adults are expected to move into insecticidal crop areas and mate with rare, resistant insects. Production of heterozygous offspring, rather than homozygous offspring reduces the rate of resistance evolution. Expectations about the refuge strategy are predicated on assumptions about when and where pest insects move and mate. Accumulating evidence indicates that the behavior of western corn rootworm beetles, Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae) (WCR), in refuge and corn rootworm (CRW)-active Bt-transgenic maize does not always conform to assumptions about random mating and individual movement. Contrary to expectations, up to 23.6% of unmated refuge females left refuge and were non-teneral by the time they mated in CRW-active maize. Consequences of protandry, limited male mating capacity, premating male and female movement patterns, skewed sex ratios, and delayed adult emergence from CRW-active maize all may contribute to unexpected or undesirable patterns of WCR reproductive behavior. Modeling suggests that temporal and spatial components of WCR mating that limit interactions in block refuges can be reduced by deploying blended refuges.

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