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United States Department of Agriculture

Agricultural Research Service

Research Project: ECOLOGICALLY-BASED PEST MANAGEMENT STRATEGIES FOR WESTERN COTTON

Location: Pest Management and Biocontrol Research

Title: Bt Crop Effects on Functional Guilds of Non-target Arthropods: A Meta-Analysis

Authors
item Wolfenbarger, Lareesa - U OF NEBRASKA, OMAHA, NE
item Naranjo, Steven
item Lundgren, Jonathan
item Royce, Blitzer - IA STATE UNIV, AMES, IA
item Watrud, Lidia - US EPA,CORVALLIS, OR

Submitted to: PLoS One
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 10, 2008
Publication Date: May 7, 2008
Citation: Wolfenbarger, L.L., Naranjo, S.E., Lundgren, J.G., Royce, B.J., Watrud, L.S. 2008. Bt Crop Effects on Functional Guilds of Non-target Arthropods: A Meta-Analysis. PLoS One 3(5): e 2118.

Interpretive Summary: Crops genetically engineered to produce the insecticidal toxins of a common soil bacterium (Bt) are grown on vast numbers of hectares throughout the world. Despite their widespread use and considerable research, uncertainty continues to persist over the potential environmental effects of these crops. Little work has examined broader impacts on ecological function of non-target species within agroecosystems. Here we conduct meta-analyses of a public database to synthesize current knowledge about the effects of Bt cotton, maize and potato on the abundance and interactions of arthropod non-target functional guilds. Meta-analysis is a method that allows a large number of separate studies to be quantitatively combined into a single analysis allowing more robust conclusions. We found that a number of functional guilds (predators, parasitoids, detritivores, omnivores, herbivores) are largely unaffected by Bt crops when compared to non-Bt control crops. However, in comparison with non-Bt crops sprayed with insecticides for target pest control, Bt crops harbored higher densities of members of most of these guilds. When both Bt and non-Bt crops are sprayed, arthropod abundance is similar in both. Predator to prey ratios were generally unchanged by either Bt crops or the use of insecticides. These meta-analyses are useful in informing the decisions of diverse stakeholders regarding the safety of transgenic insecticidal crops.

Technical Abstract: Uncertainty continues to persist over the potential environmental effects of crops genetically engineered to produce the insecticidal Cry toxins of Bacillus thuringiensis (Bt). Little work has examined broader impacts on ecological function of non-target species within agroecosystems. Here we use meta-analyses of a public database to synthesize current knowledge about the effects of Bt cotton, maize and potato on the abundance and interactions of arthropod non-target functional guilds. Predators were less abundant in Bt cotton compared to unsprayed non-Bt controls, and this effect was driven by reductions in two predaceous families. Fewer parasitoids were observed in Bt maize fields compared to unsprayed non-Bt controls and this pattern was driven entirely by expected reductions in a specialist parasitoid of the target pest of Bt maize. Otherwise, Bt-fields generally had similar abundance of non-target arthropods to unsprayed control fields. With the exception of detritivores and omnivores in Bt maize, the abundance of functional guilds generally increased in Bt crops compared to sprayed non-Bt controls, and type of insecticide influenced the magnitude of the effect. No differences in abundance were found in functional guilds when both Bt and non-Bt crops were sprayed. Predator to prey ratios were generally unchanged by either Bt crops or the use of insecticides. These meta-analyses are useful in informing the decisions of diverse stakeholders regarding the safety of transgenic insecticidal crops.

Last Modified: 7/25/2014
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