These services and others in natural and managed habitats amount to an estimated $57 billion annually. Predators, omnivores, and parasitoids consume insect pests and weed seeds – detritivores aid in degrading crop residue and improve soil health, and herbivores can reduce competition by non-crop plants and serve important roles as prey and hosts for natural enemies. Arthropods within agroecosystems provide numerous ecological services and economic benefits to land managers. While previous analyses contribute substantially to understanding the impacts on species and taxa, we have lacked a broader perspective of how Bt crops may affect ecological functions of the complex insect communities associated with agroecosystems. Taxonomic-specific effects on non-target orders were detected when comparing the use of Bt crops to using no pest management tactics. When Bt and insecticides are used together as a strategy compared to only insecticides, there was no consistent change in the abundance of non-target arthropods. As a single pest management strategy (i.e., no insecticide use), Bt crops reduced the abundance of non-target organisms as a group compared to using no pest management interventions, but increased abundance when Bt crops substituted for insecticides. In particular, the effect of Bt crops varied from negative to positive depending on what pest management practices were compared. A recent meta-analysis provided a broad synthesis on how Bt cotton and maize alter the abundance of non-target arthropods as a combined group. Some studies have shown negative impacts on the abundance and life history of charismatic and beneficial species (e.g., – ), leaving questions about whether GE crops have minimal ecological effects. Here, we report the first synthesis of Bt crop effects on ecological guilds and their interactions.ĭeclines in insecticide use are associated with the increasing adoption of Bt maize and cotton, and GE crops may have a reduced impact on non-target organisms relative to current pest management practices. Such a synthesis is precluded in individual studies because the number of taxonomic groups examined is limited, thus confounding ecological function and taxonomy. While researchers, regulators and policy-makers recognize the need to understand impacts of Bt crops on ecological function and associated ecosystem services such as biological pest control, these issues require the synthesis and interpretation of many studies on a diverse group of species. ![]() Currently, our understanding of the impacts of Bt crops on ecological function is limited because with few exceptions –, individual and review studies have focused almost exclusively on the taxonomic level (e.g. The potential environmental impact of these insect-resistant GE crops has been debated vigorously with most of the focus on non-target organisms, and to a lesser extent, their associated ecosystem function –. About a third of this production involves cotton and maize plants that have been engineered to produce one or more insecticidal proteins (Cry toxins) from the common soil microbe Bacillus thuringiensis Berliner (Bt) for control of lepidopteran and coleopteran pests. Growers throughout the world are rapidly adopting genetically-engineered (GE) crops with 102 million hectares produced globally in 2006. Meeting future food, feed and fiber needs without compromising environmental integrity is a central challenge for agriculture globally. ![]() Predator-to-prey ratios were unchanged by either Bt crops or the use of insecticides ratios were higher in Bt maize relative to the sprayed non-Bt control. No differences in abundance were found when both Bt and non-Bt crops were sprayed. Omnivores and detritivores were more abundant in insecticide-treated controls and for the latter guild this was associated with reductions of their predators in sprayed non-Bt maize. Numbers of predators and herbivores were higher in Bt crops compared to sprayed non-Bt controls, and type of insecticide influenced the magnitude of the difference. As expected, fewer specialist parasitoids of the target pest occurred in Bt maize fields compared to unsprayed non-Bt controls, but no significant reduction was detected for other parasitoids. Predators were less abundant in Bt cotton compared to unsprayed non-Bt controls. We compared the abundance of predators, parasitoids, omnivores, detritivores and herbivores under scenarios in which neither, only the non-Bt crops, or both Bt and non-Bt crops received insecticide treatments.
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