Measuring rootworm refuge function: Diabrotica virgifera virgifera emergence and mating in seed blend and strip refuges for Bacillus thuringiensis (Bt) maize.

Current insect resistance management plans rely on refuges of plants without Bacillus thuringiensis (Bt) toxins to provide a gene pool of unexposed insects. Insects from refuges must mate with insects from Bt maize to slow resistance evolution. We used stable isotope labeling to observe Diabrotica virgifera virgifera emergence, dispersal, physical characteristics, and mating in Bt and refuge maize planted in different refuge configurations. Our objective was to assess how refuge type facilitates mating between insects from Bt and refuge plants. Mating between D. v. virgifera beetles from different plant types was more likely in seed blends compared with strip refuges. Adult D. v. virgifera from refuge plants emerged before those from Bt plants. In strip refuges, D. v. virgifera from refuge plants did not disperse far from refuge boundaries. Larval host plant type did not affect adult size. Larger males and females were more likely to mate. Low proportions of D. v. virgifera from refuge plants were found in 5% seed blend refuges. Seed blend refuges can help to facilitate gene flow between D. v. virgifera beetles from Bt and refuge maize, but current approaches do not meaningfully contribute to delaying resistance because numbers of refuge beetles produced are insufficient. © 2018 Society of Chemical Industry.