Impact of blended and structured non-Bt refuge strategies on Helicoverpa zea (Lepidoptera: Noctuidae) adult flight parameters in corn

Helicoverpa zea (Boddie) (Lepidoptera: Noctuidae), an important pest in the Southeastern region, has field-evolved resistance to Cry toxins expressed in corn and cotton. Both crops are now being planted with pyramided events including Vip3A toxins. Insecticide resistance management (IRM) programs include required plantings of separate structured non-Bt refuge, but the planted area of structured refuge is very low. An alternative to separate structured refuge is blended refuge, where non-Bt seeds are planted directly adjacent to Bt seeds. However, this pest may be exposed to higher sublethal doses of Bt in blended compared structured refuge, which has the potential to accelerate resistance. Sub-lethal effects of Bt toxins on insects include flight capacity and adult emergence time, which can influence mating and gene exchange, ultimately impacting the Hardy-Weinberg equilibrium in a population. In 2019, five field trials were conducted in Florida, Georgia, North Carolina, and South Carolina to evaluate the impact of Bt and non-Bt plants in blended and structured refuge treatments on H. zea flight distance. Our results showed that H. zea developed on Bt maize flew farther than those developed on non-Bt maize. Comparing refuge strategies, adults developed on Bt plants on seed blends flew longer distances than adults developed on pure stand Bt plants. Our results provide important insights towards recommendations of refuge strategies to develop effective IRM plans to delay resistance. Data of this study will inform regulations concerning deployment, use of refuges, and sustainability of Bt crops.