Carol 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.

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.