Submitted to: Journal of Economic Entomology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/26/2006
Publication Date: 4/1/2007
Citation: Oyediran, I., Higdon, M.L., Clark, T.L., Hibbard, B.E. 2007. Interactions of alternate hosts, post-emergence grass control, and rootworm-resistant transgenic corn on western corn rootworm (Coleoptera: chrysomelidae) damage and adult emergence. Journal of Economic Entomology. 100:557-565. Interpretive Summary: The western corn rootworm is a major insect pest in continuous corn production, but no viable alternatives to use of insecticides for its control are available. Transgenic corn with resistance to corn rootworm larval feeding offers a viable alternative to insecticides for managing the most economically important insect pests of corn. Maintaining susceptibility to transgenic crops (resistance management) is in the interest of growers, the Environmental Protection Agency, and industry, but requires an understanding of corn rootworm biology that does not currently exist. The effects of grassy weeds, post-emergence grass control, transgenic rootworm-resistant corn and glyphosate herbicide tolerance, and the interactions of these factors on western corn rootworm damage and adult emergence was evaluated in the field. Beetle emergence from Bt corn and plant damage from Bt corn was not significantly affected by grassy weeds in either year of the study. The insect management system used (Bt corn or granular insecticide), the weed species evaluated (large crabgrass or giant foxtail), and the weed management system (weed-free, controlled when corn was very young, controlled when corn was a little older, and always weedy) all had some impact on damage to corn, number of adults emerged, sex ratio of adults, and size of adult. The most important factor was the insect management system. This information will be important to seed companies, the Environmental Protection Agency, and modelers in their attempts to develop resistance management plans for transgenic rootworm-resistant corn.
Technical Abstract: Field studies were conducted in 2003 and 2004 to determine the effects of grassy weeds, post-emergence grass control, transgenic rootworm-resistant corn expressing the Cry3Bb1 endotoxin and glyphosate herbicide tolerance (Bt corn), and the interactions of these factors on western corn rootworm, Diabrotica virgifera virgifera LeConte, damage and adult emergence. Three insect management tactics (Bt corn, its isoline, and isoline plus tefluthrin) were evaluated with two weed species (giant foxtail, Setaria faberi Herrm and large crabgrass, Digitaria sanquinalis L. Scop), and four weed management regimes (weed free, no weed management, early (V3-4) weed management and late (V5-6) weed management) in a factorial arrangement of a randomized split split-plot design. In each case, the isoline was also tolerant to glyphosate. Root damage was significantly affected by insect management tactics in both years, but weed species and weed management did not significantly affect damage to Bt corn in either year. Adult emergence was significantly affected by insect management tactics in both years and by weed species in 2003, but weed management and the interaction of all three factors was not significant in either year. The sex ratio of female beetles produced on Bt corn without weeds was generally greater than when weeds were present and this difference was significant for several treatments each year. Average dry weight of male and female beetles emerging from Bt corn was greater than beetles emerging from isoline or isoline plus tefluthrin in 2003, but there was no difference for females in 2004 and males weighed significantly less than other treatments in 2004. The implications of these results in insect resistance management are discussed.