Use of Bt-resistant caterpillars to assess the effect of Cry proteins on beneficial natural enemies

Abstract: A concern related to the use of insect-resistant Bt-transgenic plants is their potential to harm non-target organisms, especially natural enemies of important crop pests. A few studies purporting to show negative effects of Bt plants on non-target organisms had tremendous negative effects on the perception of Bt plants and on regulatory decisions. Focusing on the tri-trophic non-target studies it became evident that the design of these studies often did not account for the quality of the hosts being fed to the natural enemies. This occurred when Bt-susceptible hosts that had ingested Bt (Cry) proteins and became compromised were fed to natural enemies, causing indirect prey/host-quality mediated effects. The result was that the natural enemy often developed more slowly, had higher mortality, or decreased fecundity due to the poor host quality, not the Cry protein. Here we review studies that overcame this methodological problem in testing Cry proteins against natural enemies by feeding them strains of pest insects that had evolved resistance to Cry proteins expressed in the Bt plants. The studies utilized natural enemies from multiple orders and families of insect predators and parasitoids, and an entomopathogenic nematode. The study results provide unambiguous evidence on the lack of effects of these Cry proteins on important natural enemies and provide guidance for future non-target studies. These data confirm the large and sound body of literature demonstrating that the Cry proteins currently used in Bt crops for control of Lepidoptera are not harmful to natural enemies that are important for biological control of these and other pest species.