Sentinel monitoring for resistance to Bt toxins in European corn borer (Lepidoptera: Crambidae) in Canada.

Transgenic corn Zea mays (L.) producing Bacillus thuringiensis insecticidal toxins (Bt corn) has successfully controlled the European corn borer Ostrinia nubilalis (Lepidoptera: Crambidae), one of the most destructive corn pests in North America, for over 25 years. However, field-evolved resistance to Cry1Fa toxin was first documented in Nova Scotia, Canada, in 2018, with subsequent detections in Quebec and Manitoba. Before these discoveries, no resistance had been reported in O. nubilalis populations to Bt toxins, despite ongoing resistance monitoring mandated by regulatory agencies. Sentinel plots monitored in Canada during 2019 to 2023 reveal the first cases of resistance in O. nubilalis populations to Cry1Ab and Cry1A.105 toxins. Laboratory bioassays of field-derived populations corroborate these findings. This study serves as a case study demonstrating the value of sentinel plots for detecting field-evolved resistance and providing critical insights into regional resistance dynamics. Enhanced surveillance, particularly in regions with low Bt corn acreage, is essential to mitigate the spread of resistance and preserve Bt corn technology. This study underscores the need for robust and integrated monitoring frameworks to sustain the efficacy of Bt crops and prevent the resurgence of a historically significant corn pest.