Setting the mood: Effects of various Bt corn refuge configurations on mate selection of the western corn rootworm

The western corn rootworm, or WCR, (Diabrotica virgifera virgifera) is the most significant pest of field corn in the United States, and has recently expanded its range into Europe. Since 2004, hybrid corn containing Bt toxins targeting the corn rootworm complex have been heavily adopted and are now the primary control measure for this pest in North American corn production. The evolution of resistance is an ongoing concern, and to ensure Bt products will retain their usefulness, insect resistance management (IRM) tactics using various refuge structures have been adopted. One of the key tenets of the refuge strategy is that males and females emerging from Bt and refuge plantings mate randomly. A violation of this largely untested assumption would lead to acceleration of resistance development. To generate empirical field data on mating rates between beetles emerging from Bt and refuge plants, we used field cage studies of field populations of WCR in Indiana. Various refuge configurations were tested; all refuge plants were labeled using the stable isotope N15. This mark persists in the elytra of adult beetles after eclosion, allowing for collection and analysis of isotopic ratios of beetles in mating pairs. We used this approach to test the random mating assumption in Bt and refuge beetles collected from field cages. Other data collected include emergence rates, timing and sex ratios. These data will then be evaluated in the context of existing IRM strategies and used to highlight opportunities to improve current refuge strategies in order to facilitate random mating.