Status of Bt resistance in European corn borer (Lepidoptera: Crambidae) populations within Minnesota and Wisconsin

Transgenic Bt corn is one of the most successful modern control methods for stalk-boring insect pests. Specifically devised to target the European corn borer, Ostrinia nubilalis (Hübner), Bt crops expressing insecticidal Cry proteins significantly reduced feeding injury from O. nubilalis, which previously cost U.S. growers over $1 billion USD annually in control efforts and yield loss. Compared to chemical insecticides, Bt technology poses little risk to non-target organisms and reduces adverse effects on the environment. However, large-scale reliance on Bt crops places immense selection pressure on O. nubilalis to evolve resistance to Bt technology, threatening the continued success of this technology. Recent studies have identified widespread practical resistance in O. nubilalis to Cry proteins in Canada. A field of Bt sweetcorn expressing Cry1A.105 and Cry2Ab2 proteins in Connecticut also experienced severe damage from O. nubilalis. The existence of resistant populations of O. nubilalis in Canada and U.S. poses a concern that resistant alleles will proliferate in this highly mobile insect within the Corn Belt. Currently, there is a lack of data regarding the extent of Bt resistance in O. nubilalis populations in the U.S. For this study, we used F₂ screening methods to determine the susceptibility of field-collected O. nubilalis from Minnesota and Wisconsin to pre-determined diagnostic doses of Cry1F, Cry1Ab, Cry1A.105, and Cry2Ab2 Bt proteins utilizing diet-overlay bioassays. The results of these bioassays have important implications for Bt resistance monitoring and management, which can assist in amending current resistance management practices and preserve the benefits of Bt crops.