D3031: F₂ screening for Cry1A.105 resistance in European corn borer (Ostrinia nubilalis) field populations from Ohio

Early detection of resistance alleles in pest populations is essential to maintaining the long-term effectiveness of Bt crops. In this study, we utilized the F₂ screening technique to detect potential resistance to Cry1A.105 in field-collected populations of Ostrinia nubilalis (European Corn Borer). Unlike standard dose-response or diagnostic dose methods, F₂ screening allows for the identification of rare, recessive resistance alleles before they reach high frequencies in the field. Larvae were collected from Ohio, and a total of six iso-line families were successfully established. Single-pair matings were used to generate the F₁ generation, which was then mass-mated to produce F₂ offspring. To assess resistance, we conducted overlay bioassays exposing F₂ neonates to Cry1A.105-treated diet. A total of 128 larvae for each iso-line were tested for survival following exposure. Resistance in the F₂ generation was evaluated by observing survival rates, which may indicate homozygous or heterozygous resistance in the parental lines. This approach not only enhances our ability to detect low-frequency resistance alleles but also supports improved insect resistance management (IRM) strategies. While the project is still ongoing and results are not yet available, the study highlights the value of F₂ screening for proactive monitoring of Bt resistance in ECB populations. The results will help inform recommendations for resistance management and sustainable use of Bt technologies in corn production.