Impact of seed-blend and structured refuges on Helicoverpa zea mating success and fecundity in Bt and non-Bt corn

Helicoverpa zea (Boddie) is a pest of regulatory concern that has evolved resistance to Cry toxins expressed in Bt crops. The USEPA relies on pest biology and ecology to evaluate resistance management plans for Bt crops, requiring up-to-date scientific information to guide regulatory decisions. Our research characterized the impact of seed-blends versus structured refuges on H. zea fitness. In 2024, we planted five combinations of corn (100% non-Bt (structured refuge), 100% Cry, 80% Cry & 20% non-Bt (seed-blend), 100% Cry+Vip, and 80% Cry+Vip & 20% non-Bt) at five locations in North and South Carolina. When we observed late-instar larvae, we collected ears from each treatment and placed them into bins with sand, sifting them weekly to collect and weigh pupae. We paired 2-5 day-old female moths with 2-5-day-old lab-reared males. We housed pairs in cups with cheesecloth as a lid and oviposition substrate. We replaced cheesecloth on days one, two, three, five, and seven. We transferred cheesecloth containing eggs to a container with a damp cotton ball. After five days, we counted the number of neonates. The 100% Cry and 20% non-Bt (Vip seed-blend) were more likely to have neonates than the 80% Bt (Cry seed-blend) and the 20% non-Bt (Cry seed-blend). More neonates from 100% Cry hatched on days four and five than from non-Bt ears from the Cry+Vip seed-blend. These data will provide the EPA with information on H. zea fecundity to support the development of regulations regarding refuge deployment, Bt crop use, and long-term sustainability.