Feeding Stimulants for the European Corn Borer (Lepidoptera: Pyralidae): Additives to a Starch-Based Formulation for Bacillus thuringiensis

A starch formulation of Bacillus thuringiensis Berliner is being developed as a component in a pest management system to control Ostrinia nubilalis (Hübner). Palatability is one property of starch formulations which must be investigated; this study was done to identify materials that will cause O. nubilalis larvae to feed readily on starch granules. A two-choice behavioral bioassay was developed for evaluating phagostimulants in starch granules (without B. thuringiensis). Various materials were tested: compounds reported in the literature as feeding stimulants, the artificial diet for the species, corn foliage. corn oil, and the commercial feeding stimulant, Coax. Starch granules without additives were seldom fed upon by larvae, but it was possible to make the granules even more acceptable to larvae than corn foliage. The best feeding responses were to mixtures containing lipid, sugar, and protein. Coax was the most effective material tried; for example, in bioassays, the ratio of larvae that chose granules with Coax over those with only starch was 320:1, and the ratio of larvae choosing granules with Coax over corn leaf disks was 11.5:1. In greenhouse tests, phagostimulants increased the effectiveness of granules containing B. thuringiensis for killing O. nubilalis larvae. For example, when Coax was added to the granules, the amount of B. thuringiensis used could be reduced by 75% without reducing mortality.