Effects of Transgenic Bacillus thuringiensis Corn and Permethrin on Nontarget Arthropods 1

Planting of insect-resistant transgenic corn has led to con- cerns about potential effects on nontarget arthropods. Various sampling meth- ods (visual counts, yellow sticky cards, pitfall traps) were used at 7-to 10-day intervals to test for possible changes in abundance for common nontarget arthropods caused by transgenic or insecticide-based pest management. Large- scale field studies arranged in randomized complete blocks were conducte di n 2001 and 2002 in central Iowa. Treatments included Bt corn (Pioneer 34M95, event MON810), a nonBt isoline (Pioneer 34M94), and the nonBt isoline treated with permethrin (Pounce 1.5G). There was high variation in popula- tion estimates for the majority of the arthropods collected. Consequently, only data from taxa with coefficients of variation 75 using a particular sampling method were used in statistical analysis. Insecticide applications negatively impacted populations of arachnids (Araneae and Opiliones), Cantharidae, Ela- teridae and Macrocentrus cingulum (Hymenoptera: Braconidae). In the trans- genic treatment, fewer M. cingulum and Nitidulidae were present, presumably because of a lack of Ostrinia nubilalis (Lepidoptera: Crambidae), which serve as hosts for M. cingulum and provide habitat for Nitidulidae, which are known to frequent O. nubilalis tunnels. However, application of a conventional insec- ticide for O. nubilalis control had a broader impact on populations of various nontarget arthropods. These results are consistent with other studies that suggest nontarget impacts resulting from insecticides may be greater than those caused by Bt corn.