Quantifying exposure pathways in generalist predator food webs: Uptake of Bt-endotoxins across multiple transgenic events

Despite the reported specificity of Bacillus thuringiensis proteins against target pests, uptake of Bt-endotoxins from genetically engineered crops has occassionally been reported as affecting the fitness of natural enemies. It is therefore essential to quantify exposure pathways in non-target arthropod food webs across multiple transgenic events. Adult ground beetles (Coleoptera: Carabidae) were collected from fields of transgenic corn resistant to the corn borer (expressing Cry1Ab), corn rootworm (Cry3Bb1), stacked for resistance to both pests (Cry1Ab & Cry3Bb1), and a non-transgenic isoline and screened for Cry1Ab Bt-endotoxins using enzyme-linked immunosorbent assays. Significant numbers of carabids tested positive for Cry1Ab from the corn borer-resistant field: Cratacanthus dubius (50%), Clivina bipustulata (50%), Harpalus pensylvanicus (39%), Cyclotrachelus sodalis (20%) and Stenolophus comma (4%). The highest proportion of Bt-endotoxin uptake was 4-6 weeks post-anthesis. Only 5% of one species, H. pensylvanicus, screened positive from the corn rootworm-resistant field, despite similar expression of Bt-endotoxins in plant tissue from rootworm- and corn borer-resistant events. This difference in Cry1Ab uptake could be due to changes in the non-target food web or differential rates of Bt-endotoxin decay between genetic events. This study has therefore quantified the differential uptake of Cry1Ab Bt-endotoxins by the carabid community across multiple transgenic events, thus forming the basis for future risk-assessment of transgenic crops.