Ground beetle acquisition of Cry1Ab from plant- and residue-based food webs

Ground beetles are significant predators in agricultural habitats. While many studies have characterized effects of Bt maize on various carabid species, few have examined the potential acquisition of Cry toxins from live plants versus plant residue. In this study, we examined how live Bt maize and Bt maize residue affect acquisition of Cry1Ab in six species. Adult beetles were collected live from fields with either current-year Bt maize, one-year-old Bt maize residue, two-year-old Bt maize residue, or fields without any Bt crops or residue for the past two years, and specimens were analyzed using ELISA. Observed Cry1Ab concentrations in the beetles were similar to that reported in previously published studies. Only one specimen of Cyclotrachelus iowensis acquired Cry1Ab from two-year-old maize residue. Three species acquired Cry1Ab from fields with either live plants or plant residue (Cyclotrachelus iowensis, Poecilus lucublandus, Poecilus chalcites), implying participation in both live-plant and residue-based food webs. Two species acquired toxin from fields with live plants, but not from fields with residue (Bembidion quadrimaculatum, Elaphropus incurvus), suggesting participation only in live plant-based food webs. One species did not acquire Cry1Ab from either live-plant or residue (Scarites quadriceps), suggesting that its food sources might not contain significant amounts of Cry1Ab. These results revealed significant differentiation among carabid species in their associations with live-plant and residue-based food webs in agricultural fields.