BackgroundUncertainty persists over the environmental effects of genetically-engineered crops that produce the insecticidal Cry proteins of Bacillus thuringiensis (Bt). We performed meta-analyses on a modified 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.Methodology/Principal FindingsWe 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. Predators were less abundant in Bt cotton compared to unsprayed non-Bt controls. 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. 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. 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. No differences in abundance were found when both Bt and non-Bt crops were sprayed. 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.Conclusions/SignificanceOverall, we find no uniform effects of Bt cotton, maize and potato on the functional guilds of non-target arthropods. Use of and type of insecticides influenced the magnitude and direction of effects; insecticde effects were much larger than those of Bt crops. These meta-analyses underscore the importance of using controls not only to isolate the effects of a Bt crop per se but also to reflect the replacement of existing agricultural practices. Results will provide researchers with information to design more robust experiments and will inform the decisions of diverse stakeholders regarding the safety of transgenic insecticidal crops.

This dissertation is dedicated to Henry F. Swanson, Extension Director Emeritus of Orange Coimty, Florida, who has patiently observed over 4,000 initial arrival times of Red Admiral Butterflies during the past 18 years, and who shares my interest in and imderstanding of their behavior.

The degree of abundance and diversity of springtails (order Collembola) often indicates the extent of disturbance by various agricultural practices. We examined how transgenic herbicide-tolerant soybean varieties and their associated weed management systems affect the abundance of 21 surface-active springtail species during three successive soybean growing seasons. With six soybean varieties (three transgenic, three nontransgenic), we tested three weed management systems: (1) targeted application of speciÞc herbicides to the corresponding tolerant transgenic varieties; (2) conventional pre-and postemergence herbicide applications; and (3) mechanical cultivation. Each method posed its own potential costs and beneÞts to springtails. In targeted plots, springtail numbers were similar to or higher than those in conventional plots, suggesting that the later and repeated targeted applications to transgenic soybeans do not adversely affect springtail numbers in the short term. We attributed the observed treatment effect differences on springtail numbers to resultant differences in weed cover and degree of soil disturbance (indirect effects), rather than to any direct toxic effects of the herbicides. The treatments affected some species but not others; most of the affected species responded similarly to differences in weed treatment. Our results overall suggested no deleterious short-term effects of transgenic soybean targeted weed-management systems on abundance of the springtail species examined.

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