Clinton D. Pilcher

Field evaluation of the impact of corn rootworm (Coleoptera: Chrysomelidae) -protected Bt corn on foliage-dwelling arthropods

Abstract A 3-yr field study was conducted in Monmouth, IL, to evaluate the effect of transgenic Bt corn expressing a Cry3Bb1 protein (MON 863) on foliage-dwelling arthropods. The study employed a split-plot design with MON 863 corn and a conventional non-Bt near isoline (RX670) as the main plots and insecticide regimens (no insecticide, imidacloprid applied as seed treatment, tefluthrin applied as soil treatment, and permethrin applied as foliar treatment) as subplots. Foliage-dwelling arthropods were sampled with sticky traps during each of the 3 yr (2000–2002). The most abundant taxa collected included corn pests, such as Diabrotica virgifera virgifera LeConte and Chaetocnema pulicaria Melsheimer (Coleoptera:Chrysomelidae), and Rhopalosiphum maidis Fitch (Homoptera:Aphididae). The most abundant generalist predators captured by sticky traps were Coccinellidae (ladybird beetles), Nabidae (damsel bugs), Orius insidiosus Say (minute pirate bugs), Syrphidae (flower flies), Chrysoperla carnea Stephens (green lacewings), Macrocentrus cingulum Rienhardt (a braconid parasitoid), and Araneae (spiders). MON 863 corn had no consistent adverse impact on the relative abundance of any nontarget foliage-dwelling arthropod taxon, including predators and parasitoids. However, insecticide applications of foliar insecticide (permethrin) significantly and consistently decreased the abundance of ladybird beetles, green lacewings, and damsel bugs compared with the insecticidal seed treatment or no insecticide application. The abundance of the pest R. maidis also was observed to increase in the foliar-applied insecticide treatment. Therefore, adoption of MON 863 and the concurrent reduction in broad-spectrum foliar-applied insecticide use for control of adult Diabrotica spp. have the potential to enhance biological control within corn agro-ecosystems.

Impact of Transgenic Bacillus thuringiensis Corn and Crop Phenology on Five Nontarget Arthropods

Abstract Large-scale field studies were conducted to determine if temporal plantings of Bacillus thuringiensis (Berliner) (Bt) corn (event 176 and Bt11) would affect the seasonal abundance of the following generalist predators: Coleomegilla maculata DeGeer and Cycloneda munda (Say) (Coleoptera: Coccinellidae), Orius insidiosus (Say) (Heteroptera: Anthocoridae), Chrysoperla carnea Stephens (Neuroptera: Chrysopidae), and one specialist parasitoid, Macrocentrus cingulum Brischke (Hymenoptera: Braconidae). Adult populations were monitored using Pherocon AM yellow sticky traps at three locations in Iowa (1996–1998). At each location, a split-plot design was used with Bt and non-Bt corn as main plots and three planting dates as the split plots. Few differences in abundance were observed between Bt and non-Bt corn for the generalist predators studied. However, M. cingulum, a specialist parasitoid of European corn borer, was significantly affected by the presence of Bt corn. Densities of adult M. cingulum were 29–60% lower in Bt corn compared with non-Bt corn. Regression analyses indicated M. cingulum adults were preferentially recruited to and subsequently increased over time in the non-Bt corn treatments at each location within each year. Significant differences were observed among planting dates for all five species. Abundance effects from Bt corn on these natural enemies were not unexpected given the foraging and searching behaviors of different species and their varying levels of dependence on the presence of European corn borer.

Biodiversity and Community Structure of Epedaphic and Euedaphic Springtails (Collembola) in Transgenic Rootworm Bt Corn

Abstract Springtails are an integral and beneficial part of the soil community. As part of an extensive study of the effect of rootworm Bt corn (Cry3Bb1) on nontarget invertebrates, we evaluated both the abundance and diversity of surface-active (epedaphic) and subsurface (euedaphic) springtails at Ames, IA, and Monmouth, IL, in 2-yr field trials during 2000–2002. Springtails were collected from pitfall traps and soil cores in plots planted with rootworm Bt corn and its non-Bt isoline. Few differences were observed in the abundance of individual species in Bt and isoline corn. Nor did the estimated species richness or the Shannon or Simpson diversity indices differ significantly between Bt and isoline corn at either location during 2000–2002, indicating no effect of Bt corn on springtail diversity. In soil insecticide-treated plots, however, springtails were consistently more abundant than in check plots, perhaps because of adverse insecticide effects on springtail predators. Soil insecticide also reduced both Shannon and Simpson diversity in the Iowa euedaphic and Illinois epedaphic populations. Such consistent insecticide effects on both abundance and diversity of springtails provide a positive control by which to assess the power of the experimental design to detect a comparable impact of Bt corn on springtails. They also show that insecticide use more strongly impacts springtails and their predators than does the practice of growing transgenic crops to control the same pests.

Effect of Planting Dates and Bacillus thuringiensis Corn on the Population Dynamics of European Corn Borer (Lepidoptera: Crambidae)

Abstract Field studies were conducted to determine how field corn, Zea mays L., phenologies in combination with transgenic Bacillus thuringiensis Berliner (Bt) corn and non-Bt (near isogenic) corn could affect egg laying by female European corn borer, Ostrinia nubilalis (Hübner), and subsequent larval injury. Transgenic Bt (events 176 and Bt11) and non-Bt corn was planted at three different times to assess the use of early- and late- planted Bt corn as a means for egg recruitment to these targeted planting dates. Plant growth stages, egg densities, and stalk tunneling was recorded at four locations in southwestern, central, and northern Iowa for three summers (1996–1998). No significant differences in egg densities were observed between Bt and non-Bt corn during the first and second generation for all three years. Significant differences did occur among planting dates. Between 50 and 100% of the eggs were laid in the early planting during the first generation. In addition, between 40 and 65% of the eggs were laid in the late planting for the second generation. Correlations between egg density and larval tunneling were inconsistent from year to year. Additional inconsistencies stemming from yearly phenological differences among sequential plantings and variable O. nubilalis populations increases the difficulty in recommending planting date adjustments as a practical management tool for European corn borer and Bt corn.

Pollen Drift from Bacillus thuringiensis Corn: Efficacy Against European Corn Borer (Lepidoptera: Crambidae) in Adjacent Rows of Non-Bt Corn

Abstract Commercial non-Bacillus thuringiensis (Bt) corn was planted adjacent to Bt corn to determine the effects of Bt corn pollen falling on non-Bt plants for control of European corn borer larvae, Ostrinia nubilalis (Hübner). Field plots in Iowa and Kansas consisted of two center rows of Bt corn with eight rows of adjacent non-Bt corn on each side. In mid-September 1996 and 1997, we counted European corn borer larvae and larval tunnels in the stalk and ear shank. There were no significant differences in European corn borer numbers across non-Bt rows and the slope of the regression line was not significantly different from zero. In a single plot in Iowa, however, fewer tunnels were observed in rows of corn that were closer to Bt corn. This site was isolated from natural infestations and probably does not reflect a typical field situation. Our results suggest that Bt pollen has minimal or no control of European corn borer larvae in adjacent rows of non-Bt corn under natural conditions. Bt pollen drifting onto adjacent non-Bt plants should not increase the risks related to resistance management.