Extrapolating non-target risk of Bt crops from laboratory to field

Authors: Duan, Jian; Lundgren, Jonathan; Naranjo, Steven; MARVIER, MICHELLE - SANTA CLARA UNIVERSITY

Submitted to: Biology Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/18/2009
Publication Date: 9/9/2009
Citation: Duan, J.J., Lundgren, J.G., Naranjo, S.E., Marvier, M. 2010. Extrapolating non-target risk of Bt crops from laboratory to field. Biology Letters. 6:74-77.

Interpretive Summary: The environmental risk posed by insect-resistant transgenic crops is currently assessed by initial laboratory tests of insecticidal proteins against many groups of beneficial non-target organisms, followed by field studies, conducted only when toxicity of the insecticidal proteins to the tested non-target organisms is demonstrated in the laboratory studies. This approach is based on the assumption that results from the laboratory toxicity studies can accurately predict the environmental risk of these crops under field conditions. To test this assumption, we performed analyses comparing results from 116 laboratory toxicity studies of Bacillus thuringiensis (Bt) insecticidal proteins with results derived from 54 independent field abundance studies. Laboratory and field studies revealed qualitatively consistent effects of Bt insecticidal proteins on many groups of nontarget organisms such as plant-feeding insects, pollinating insects and others. However, some laboratory studies predicted reduced abundances of generalist predatory natural enemies that were not realized in field studies, possibly due to the availability of alternative prey species unaffected by Bt Cry proteins. For parasitic insects, laboratory studies that incorporated the interactions of Bt plant, Bt-susceptible plant-feeding insects and parasitic wasps, better predicted the decreased field abundance of specialist parasitic natural enemies than did direct toxicity assays. Together, our findings support the validity of the central assumption underlying the current approach to risk assessment for transgenic crops.

Technical Abstract: The tiered approach to assessing the ecological risk of insect-resistant transgenic crops rests on the assumption that lower-tier laboratory studies, which expose surrogate non-target organisms to insecticidal proteins, accurately predict the ecological effects of these crops under field conditions. To test this assumption, we performed meta-analyses comparing results for non-target invertebrates exposed to Bacillus thuringiensis (Bt) Cry proteins in laboratory-based studies with results derived from independent field abundance studies. Laboratory and field studies revealed qualitatively consistent effects of Cry proteins on non-target herbivores, omnivores, detritivores, and pollinators. However, laboratory-based tritrophic studies predicted reduced abundances of generalist predators that were not realized in field studies, possibly due to the availability of alternative prey species unaffected by Bt Cry proteins. For parasitoids, laboratory studies that incorporated the tri-trophic interactions of Bt plants, Bt-susceptible herbivores, and their parasitoids better predicted the decreased field abundance of specialist parasitoids than did direct toxicity assays.