Assumptions about western corn rootworm behavior in Bt corn are not met in block refuges

The western corn rootworm (Diabrotica virgifiera virgifera LeConte, WCR) is one of the most economically important agricultural pests in the United States and Europe. Transgenic insecticidal corn hybrids expressing Bt (Bacillus thuringiensis) Cry proteins, commercialized in 2003, are widely used to control corn rootworm larvae. To delay resistance to these and other Bt corn hybrids, the EPA requires growers to plant non-Bt refuges so some susceptible beetles can develop without exposure to the Bt toxin present elsewhere in cornfields. Insect resistance management plans for rootworm Bt corn assume that mate-seeking male WCR beetles emerging from refuge plants will mate with most of the potentially-resistant females that emerge from transgenic plants. To study this assumption, male and female WCR emergence, abundance, movement and mating were measured in refuge and transgenic corn. Mating patterns and characteristics of mated females suggest refuge males may not always be abundant enough to rapidly mate receptive females. WCR populations were concentrated in or near refuges where most mating pairs were collected. Mating females collected in transgenic corn wait longer for mates than most refuge females. Peak mating in transgenic corn was late in the season when mate-seeking refuge males may be scarce. The effectiveness of block refuges and longevity of Bt technology may be affected if expectations about rootworm mating do not match what is actually happening in cornfields.