Evaluation of structured and seed-blend refuges for corn earworm (Lepidoptera: Noctuidae) using emergence cages and screen-bagged ear methods.

The corn earworm, Helicoverpa zea (Boddie), is a major lepidopteran pest of corn (Zea mays L.) in the United States and is widely managed using transgenic corn hybrids expressing Bacillus thuringiensis (Berliner) (Bt) proteins. Seed-blend refuges, in which Bt and non-Bt seeds are mixed in fixed proportions, have been widely adopted as a convenient insect resistance management (IRM) strategy. However, concerns remain about their efficiency in producing susceptible moths compared to a structured block refuge. To evaluate this, five field experiments were conducted across Texas and Georgia during 2020 to 2021 to compare adult H. zea emergence from non-Bt refuges configured as structured 100% non-Bt blocks or as 80:20 Bt/non-Bt seed blends. Adult production was quantified using two approaches: emergence cages that captured pupal-to-adult survival and screen bags that confined larvae on individual ears. Both methods yielded comparable estimates of adult H. zea emergence. Across all locations and years, seed-blend plots consistently produced fewer moths than expected based on the 20% refuge proportion, yielding 61% to 91% of the adults produced from structured refuges. Screen bag assays similarly showed reduced larval and pupal recovery from seed-blend ears. Non-Bt ears from seed-blend plots did not consistently differ from structured refuges in larval feeding intensity. Findings from this study indicate that seed-blend refuges may underperform in producing susceptible moths and may not consistently function as an effective standalone refuge strategy.