Effect of Starch-Based Corn Rootworm (Coleoptera: Chrysomelidae) Baits on Selected Nontarget Insect Species: Influence of Semiochemical Composition

Various starch-encapsulated semiochemical-insecticide formulations, developed for potential use in adult corn rootworm (Diabrotica spp.) management programs, were evaluated in the laboratory and field for effectiveness on corn rootworm beetles: a carabid, Harpalus pennsylvanicus DeGeer; and a coccinellid, Coleomegilla maculata lengi Timberlake. Carbaryl was formulated in pregelatinized starch matrices along with Diabroticaspecific semiochemicals. The specific combination of feeding-gustatory stimulants encapsulated within or coating the outside of starch granules significantly influenced effectiveness. Allstarch formulations containing feeding-gustatory stimulants effectively killed Diabrotica virgifera virgifera LeConte adults in laboratory and field bioassays. However, H. pennsylvanicus and C. m. lengi mortality was greatly reduced when presented with starch granules coated with buffalo gourd (Cucurbita foetidissima H.B.K.) root powder (contains cucurbitacin E, I, and E-glycoside) or purified cucurbitacin I. Cucurbitacin I and component(s) of buffalo gourd root powder appear to be C. m. lengi and H. pennsylvanicus antifeedants. In the field, significantly more C. m. lengi and D. v. virgifera were collected at traps baited with pollen-coated than root powder-coated starch granules. When granules were broadcast over plants, mortality of C. m. lengi was greater in plots receiving pollen-coated than root powder-coated granules whereas the opposite was observed for corn rootworm beetles. Data suggest that to optimize the effectiveness of starch baits against D. v. virgifera and to minimize adverse effects on C. m. lengi and H. pennsylvanicus, granules coated with cucurbitacin rather than with starch or pollen should be used in corn rootworm management programs