Detection methods for monitoring resistance to Bt corn (Zea mays L.) in Diabrotica virgifera virgifera (Coleoptera: Chrysomelidae)

Bt corn provides effective insect control, reducing Ontario’s insecticide use. Resistance in western corn rootworm (Diabrotica virgifera virgifera LeConte) to Bt corn (Zea mays L.) threatens the continued efficacy and benefits of this control method. The objectives of this thesis are to: (1) evaluate three bioassay methods used to monitor D. v. virgifera for resistance to the Bt proteins Cry3Bb1, Cry34/35Ab1, and mCry3a; (2) determine if resistance has occurred to Bt corn in D. v. virgifera high-risk areas in Ontario and Michigan; and, (3) develop recommendations for future resistance monitoring and management for both current and novel insect control tactics. D. v. virgifera were collected from fields in 2012 and 2013 and the susceptibility of beetles to Bt proteins was evaluated using diet, whole plant, and seedling bioassays. Results confirm that resistance to Cry3Bb1 and mCry3a occurred in some areas of Michigan, but not in Ontario. Confirmed resistance close to the Canadian border serves as a warning that resistance is likely to occur in Canada, especially if single Bt proteins continue to be deployed with current insect resistance management practices. Findings highlight the importance of incorporating insect resistance management into integrated pest management to prolong the efficacy of current and future D. v. virgifera management tactics.