Monday, December 10, 2007 - 9:05 AM

Estimating carabid beetle exposure to rootworm-resistant Bt protein

Miles Lepping,, Galen P. Dively,, Paula M. Shrewsbury,, Leslie Pick,, and Zain Hasan, University of Maryland, 4112 Plant Sciences Bldg, Dept. of Entomology, College Park, MD

A laboratory and field study determined the half-life of detectability and estimated field exposure to Cry34Ab1 Bt-corn protein for the non-target ground beetle, Elaphropus xanthopus (Coleoptera: Carabidae). Using quantitative enzyme-linked immunosorbent assay (ELISA), whole-body adult ground beetles were screened for the presence and quantity of Cry34Ab1 protein, which largely predicts toxicity for the target pest, corn rootworm (Diabrotica spp.). Laboratory half-life studies estimated Cry34Ab1 protein remaining in beetles following consumption of a single Bt-pollen meal at post-consumption time periods ranging from 0 96 h. The half-life of detectability for pollen-borne Cry34Ab1 in adult E. xanthopus was approximately 8.3 h, with detectability ending before 24 h. In order to estimate laboratory dosing, we examined frass produced by E. xanthopus for Cry34Ab1 protein during long-term studies that included a Bt-pollen-only diet. Elaphropus xanthopus frass yielded approximately 40% of the Cry34Ab1 protein found in Cry34/35Ab1 pollen. In field experiments, E. xanthopus were collected during pollen shed from both Cry34/35Ab1 and non-Bt field corn plots, and screened using ELISA for the presence and quantity of Cry34Ab1 protein. Of adult E. xanthopus collected from field plots planted with Cry34/35Ab1 field corn, 86% tested positive for the presence of Cry34Ab1 (3.60.5 ng/mg), whereas 54% tested positive in non-Bt (2.20.8 ng/mg) corn plots approximately 60 m away. While field results underscore the need for larger test-plot size in community studies examining transgenic toxins, Cry34Ab1 concentrations found within field-exposed E. xanthopus were below laboratory doses found to cause no effects on adult performance in long-term studies.

Species 1: Coleoptera Carabidae Elaphropus xanthopus