Long-Term Assessment of the Effects of Transgenic <I>Bt</I> Cotton on the Abundance of Nontarget Arthropod Natural Enemies

Abstract

Abstract A 6-yr field study assessed the long-term impact of Bt cotton producing the Cry1Ac δ-endotoxin on 22 taxa of foliar-dwelling arthropod natural enemies in Arizona. No chronic, long-term effects of Bt cotton were observed over multiple generations of nontarget taxa. Zero-2 taxa declined significantly in unsprayed Bt compared with non-Bt cotton each year. In contrast, positive control studies showed that insecticide applications for caterpillars and other pests in both non-Bt and Bt cotton had much greater negative effects on 10 taxa. Multivariate principal response curves supported the findings of univariate analyses for the entire natural enemy community, showing no effect of Bt cotton but large and long-lasting negative effects from the use of insecticides. Multi-year analyses provided greater statistical power and indicated significant reductions that averaged 19% in five arthropod predator taxa in unsprayed Bt compared with non-Bt cotton. Most of these reductions were likely associated with red...