During the summers of 2000 and 2001, we devoted 32-hectares near Champaign, Illinois, to an experiment designed to create phenological differences in corn, Zea mays L., and soybean, Glycine max, to evaluate their potential impact on the ovipositional behavior of the new variant of western corn rootworm (WCR), Diabrotica virgifera virgifera LeConte. A smaller version of this trial (6.7-hectare), near Monmouth, Illinois, where this WCR variant is not located, served as our control. In Champaign, Illinois, an intense crop rotation area, adult densities (vial traps) increased significantly in soybean after corn developed past the R2 developmental stage (brown silk, cob full sized, blister stage). From soil samples, I determined that significantly more eggs were laid in soybean and late-planted corn (10.8 - 5.45 eggs/ 0.5 liter), respectively, than in early-planted corn (4.3 eggs/ 0.5 liter). Results from Monmouth, Illinois, where crop rotation selection pressure has been historically low, showed adult densities increased significantly in late-planted corn after corn developed past the R2 developmental stage. Significantly more WCR eggs were oviposited in late-planted corn (9.5 eggs/ 0.5 liter) compared with early-planted corn (6.8 eggs/ 0.5 liter). Soybeans were not used as an egg-laying site (0.0 eggs/ 0.5 liter). We believe the WCR variant in east central Illinois responds to differences in corn and soybean phenology. In east central Illinois, soybeans and late-planted corn are both competitive sinks for WCR eggs. In northwestern Illinois, western corn rootworms are not common inhabitants of soybean fields. Consequently, soybeans are not used as egg-laying sites.
Species 1: Coleoptera Chrysomelidae Diabrotica virgifera virgifera (Western corn rootworm)
Keywords: oviposition
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