Submitted to: Journal of Arachnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2010
Publication Date: 6/25/2011
Citation: Peterson, J.A., Lundgren, J.G., Harwood, J.D. 2011. Interactions of transgenic Bacillus thuringiensis insecticidal crops with spiders (Araneae). Journal of Arachnology. 39(1):1-21. Interpretive Summary: Spiders are an important group of predators in agroecosystems, and this review examines the implications of widespread planting of Bt crops on spider populations and communities. Spiders may be affected by Bt toxins both directly (e.g., feeding on pollen, root exudates, or on the leaf tissues), or indirectly (e.g., consuming prey that is contaminated or sick). Currently, there are no consistent negative effects of Bt crops on spiders described, and insecticide use likely harms spider populations more than the alternative Bt crops do. However, discrepancies in the literature suggest that the ecological effects of Bt crops are somewhat biased, including inconsistent sampling regimens, low taxonomic resolution (spiders are diverse, but are usually lumped together as “spiders” in these studies), and how the changes to the agroecosystems might affect spiders in non-toxic ways.
Technical Abstract: Genetically modified crops expressing insecticidal proteins from Bacillus thuringiensis (Bt) have dramatically increased in acreage since their introduction in the mid-1990’s. Although the insecticidal mechanisms of Bt target specific pests, concerns persist regarding direct and indirect effects on non-target organisms. In the field, spiders may be exposed to Bt toxins via multiple routes, including phytophagy and pollenivory, consumption of Bt-containing prey, and soil exudates in the detrital food web. Beyond direct toxicity, Bt crops may also have indirect impacts, including pleiotropic and prey-mediated effects. Here, we comprehensively review the literature and use meta-analyses to reveal that foliar spider abundance is unaffected by Bt corn and eggplant, while cotton and rice revealed minor negative effects and positive effects from potato. Moreover, the soil-dwelling community of spiders was unaffected by Bt corn and cotton, while positively impacted in potato. However, when non-Bt crops are applied with insecticides, as is the norm in conventional agriculture, both foliar and epigeal spiders are positively affected by Bt crops. The current risk-assessment literature has several caveats that could limit interpretations of the data, including lack of taxonomic resolution and sampling methods that bias the results in favor of certain spiders. These families responded differently to Bt crops and spider responses to insecticides are species- and toxin-specific, thus highlighting the need for greater taxonomic resolution. Bt crops have become a prominent, and increasingly dominant, part of the agricultural landscape; understanding their interactions with spiders, a diverse and integral component of agroecosystems, is therefore essential.