Characterizing responses of rotation-resistant and rotation-susceptible populations of the western corn rootworm to Bt corn using a greenhouse bioassay

The western corn rootworm (Diabrotica virgifera virgifera LeConte) is one of the most economically important pests of corn (Zea mays L.). Historically, crop rotation has been highly effective for preventing damage caused by western corn rootworm larvae in the United States. However, much of the eastern Corn Belt now hosts populations of this insect that circumvent crop rotation by ovipositing in crops other than corn. The goal of this greenhouse experiment was to determine if rotation-resistant and rotation-susceptible western corn rootworm larvae differ with respect to survival or development on corn expressing one or more Bt toxins—another highly popular management tactic. A single-plant bioassay was used. Corn plants were infested with 225 near-hatch eggs at the V5 growth stage (five leaf collar). Larvae were allowed to develop undisturbed on the root systems for 17 days, after which they were recovered using Berlese funnels. Larvae were counted to estimate mortality; head capsule widths were recorded to assess development. No difference between rotation-resistant and rotation-susceptible larvae with respect to mortality caused by exposure to Bt toxins was observed. Head capsule widths suggest that larvae from these two populations develop similarly when reared on Bt corn. Potential explanations for the observed results are discussed.