Genetic basis of Cry2Ab2 resistance in European corn borer (Lepidoptera: Crambidae) populations derived from multiple locations in the Upper Midwest

The European corn borer (ECB), Ostrinia nubilalis, is a significant pest of corn, historically costing growers $1 billion annually in combined control measures and yield loss. Since 1996, transgenic Bt corn has been used as a main control method for ECB and successfully suppressed regional populations. However, after nearly three decades of use, the continued benefits of Bt corn technology for ECB management are now seriously threatened. Beginning in 2018, multiple ECB populations resistant to Cry1 proteins were identified in Canada. More recently, field-evolved resistance to Cry1A.105 and Cry2Ab2 sweetcorn was documented in Connecticut, U.S. during 2023-2024. More concerning, our F2 screens of ECB populations collected in Minnesota and Wisconsin during 2023-2024 suggested a high resistance allele frequency of Cry2Ab2 in the field. To delay insect resistance development, the U.S. EPA has implemented two main insect resistance management (IRM) strategies: high dose/refuge and gene-pyramiding. The success of these strategies depends on several critical assumptions, including recessive inheritance, absence of cross-resistance, and redundant killing. Therefore, assessing the validity of these assumptions is essential for sustainable pest control and resistance management. In this study, we detailed the genetic basis of Cry2Ab2 resistance in ECB populations derived from multiple locations in the upper Midwest using F2 screens. Our analyses included inheritance characterization, cross-resistance patterns, and inter-strain complementation tests. The results have important implications for the continued efficacy of Bt corn technology and management of ECB populations.