Labortory Bioassays for Evaluating Sweet Corn Antibiosis on European Corn Borer (Lepidoptera: Pyralidae) Larval Development

Abstract

European corn borer (Ostrinia nubilalis Hübner) can severely affect commercial sweet corn quality during years of heavy infestation. The isolation and identification of allelochemicals in sweet corn which detrimentally affect O. nubilalis may enhance breeder selection for greater ear feeding resistance, thus reducing the need for insecticide application. Field selection techniques for improving plant resistance to O. nubilalis cannot easily distinguish between plant tolerance or antibiosis. A laboratory bioassay incorporating ear tissues from field resistant and susceptible sweet corn genotypes into a nutritionally complete O. nubilalis larval diet was developed as an initial step to facilitate the isolation and identification of potential chemical resistance factors in sweet corn. Neonates reared for 7 d on a meridic diet with limited fungal and bacterial contaminant control agents weighed more than larvae grown on a comparable diet with high levels of contaminant control (5.96 and 2.46 mg, respectively). Silk tissue from several sweet corn genotypes significantly reduced larval weight and increased total larval development time compared with kernel tissue. Silk tissues incorporated on a weight basis had volumes about 3 × that of an equal weight of kernel tissues. However, tissues incorporated into a specific diet volume on a weight or volume basis usually did not alter larval weight or time to pupation within a genotype. Incorporation on a weight basis was most time efficient. Future bioassays screening for antibiotic effects of sweet corn tissue on O. nubilalis development should utilize a diet with limited contaminant control agents, incorporate tissue on a weight basis, and focus on silk tissue.