Evaluation of noncorn host plants as a refuge in a resistance management program for European corn borer (Lepidoptera: Crambidae) on Bt-corn

Abstract

Studies in New York and Pennsylvania compared egg mass recruitment and larval survival on com and other hosts of the European corn borer, Ostrinia nubilalis (H[umlaut]ubner), to assess the potential of these plants to act as a refuge in a resistance management program. Assessments were made on replicated plantings and natural plant stands in the field and under controlled conditions in the laboratory, Scouting of mixed field plantings revealed more egg masses on corn than any other crop or weed species. At least twice as many larvae per plant were recovered from naturally infested corn compared with the next best host plant across both years. Larval recovery from noncorn host plants varied widely. Fewer adults emerged from overwintering weed stubble than from corn stubble, and the parasitoid Macrocentris grandii (Goidanich) was found associated only with com stubble. Survival on plants infested with corn borer larvae was consistently higher on corn than on other plants. In a laboratory study, the number of corn borer tunnels in com was double the next best host, ragweed. Noncorn hosts appear unlikely to provide a substantial number of corn borer individuals susceptible to B. thuringiensis (Berliner) in comparison with the number expected from the 20% planting refuge mandated by EPA registration of Bt-corn. Evidence from these studies do not support a recommendation of reduced refuge planting areas in the northeastern United States.