Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/20/2005
Publication Date: 10/3/2005
Citation: Lopez, M.D., Prasifka, J.R., Bruck, D.J., Lewis, L.C. 2005. Utility of ground beetle species in field tests of potential non-target effects of Bt crops. Environmental Entomology. 34(5):1317-1324.
Interpretive Summary: The adoption of transgenic crops has led to safety concerns regarding any potential unintended effects to non-target organisms including ground beetles. This study examines ground beetle populations in order to pinpoint one or more species that can be used as indicators of overall population trends, and to test for treatment effects of Bacillus thuringiensis (Bt) and insecticide treated corn. Ground beetles are common inhabitants of agricultural fields and are exposed to transgenic crop production. The feeding habits of ground beetles are wide-ranging, and present various avenues by which exposure to Bt crops could occur including direct consumption of transgenic plant material, as well as foraging on live or dead organisms that have fed on transgenic plant material. Thirty-seven species of ground beetles were sampled using pitfall traps in two Iowa locations in transgenic, non-transgenic, and insecticide-treated non-transgenic corn. Ground beetle collections indicated that Harpalus pensylvanicus would be the best choice for an indicator species in corn grown in the Midwest. H. pensylvanicus is common, has omnivorous feeding habits, and is easily sampled in large numbers. No ground beetle species had a significant effect due to transgenic corn, and only one species, H. pensylvanicus, was significantly impacted by the use of an insecticide. A subsequent analysis was conducted to determine the scale of a sampling program necessary to test for significant effects with sufficient power. This analysis demonstrated that while only one species had a significant effect in the sampling program used, it would take many more replications to elucidate a small effect. This information will be useful for all scientists and stakeholders interested in potential unintended effects of transgenic crops.
Technical Abstract: Ground beetle (Coleoptera: Carabidae) characteristics including distribution, diet breadth, and importance as generalist predators make them candidates for evaluating potential unintended effects of transgenic crops. The abundance and composition of carabids collected from pitfall traps placed in Iowa hybrid dent corn were used to determine if one or more species can be used as representatives of carabid communities, and to test for differences in carabid populations due to transgenic Bacillus thuringiensis (Bt) or insecticide-based pest management. Power analyses were also used to evaluate the adequacy of the experimental design. Carabid collections indicated Harpalus pensylvanicus DeGeer would be the best choice of a single indicator species based on its apparent ubiquity and abundance in Iowa and other corn-producing states. However, population levels were time-dependant, and composition of carabid communities differed between locations. Considering the numerical dominance of a few species per field, identification of the two to four most abundant species might be used to effectively represent local carabid communities. Harpalus pensylvanicus populations were impacted by insecticide use, but no effects of Bt were found. Power analyses indicated that with the experimental design and replication used, only large effects were detectable; based on the variation between plots, increased replication is needed to make detection of either moderate (30-50%) or small (< 30%) effects likely. The recent release of transgenic corn with coleopteran toxicity highlights the importance of these results when evaluating potential unintended effects on ground beetles. One species not previously recorded in Iowa, Lebia pulchella Dejean, also was collected.