Field Evaluation of the Impact of Corn Rootworm (Coleoptera: Chrysomelidae)–Protected Bt Corn on Ground-Dwelling Invertebrates

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 ground-dwelling invertebrates. The study employed a split-plot design with MON 863 corn and a conventional near isoline (RX670) as the main plots, and insecticide regimens as subplots. Ground-dwelling arthropods were sampled with pan and pitfall traps during each of the 3 yr (2000–2002). The most abundant taxa collected included generalist predators, such as Araneae (spiders), Carabidae (ground beetles), and Staphylinidae (rove beetles), and detritivores (decomposers), such as Japygidae (diplurans), Lathridiidae (scavenger beetles), Formicidae (ants), Chilopoda (centipedes), and Oligochaeta (earthworms). MON 863 had no consistent adverse impacts on the abundance of any nontarget, ground-dwelling taxon compared with the non-Bt isoline; significant line effects were seen with only 2 of 14 nontarget taxa analyzed, and the nature of these effects varied within and among years. In contrast, certain insecticide applications had consistent adverse impacts across all 3 yr on diverse groups of ground-dwelling predators such as spiders and decomposers like diplurans. Foliar (permethrin)- and soil (tefluthrin)-applied insecticides significantly decreased the abundance of ground beetles and spiders compared with an insecticidal seed treatment (imidacloprid) or no insecticide application. Overall, significant effects of insecticide regimen were seen with 6 of the 14 nontarget taxa analyzed. Adoption of MON 863 and the concurrent reduction in broad-spectrum soil-applied insecticide use for the control of larval Diabrotica spp. have the potential to enhance the role of biological control within corn agroecosystems.