L. LaReesa Wolfenbarger

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

Background Uncertainty 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 Findings 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. 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/Significance Overall, 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.

POSTFLEDGING SURVIVAL AND MOVEMENT IN DICKCISSELS (SPIZA AMERICANA): IMPLICATIONS FOR HABITAT MANAGEMENT AND CONSERVATION

Abstract When land managers incorporate the habitat needs of grassland birds into their planning, they typically rely on management recommendations based on habitat use by adults during nesting. Habitat requirements for other critical life stages are seldom known and may differ from those of nesting adults. Using radio-telemetry, we examined survival and habitat use by juvenile Dickcissels (Spiza americana) during the postfledging period. In 2003 and 2004, we monitored 60 fledgling Dickcissels for ≤30 days after they left the nest. Mortality rates were highest during the first week after leaving the nest, and only 33% of the fledglings survived the first four weeks after leaving the nest. Estimated mean survival times were 16.9 ± 1.6 days after birds left the nest. In both years, fledgling survival was positively associated with dense vertical and horizontal structure of forbs at nests. Survival tended to be positively associated with vertical grass density on adult territories and negatively associated with patchily distributed forbs on adult territories. Fledgling habitat use was restricted to areas where Dickcissels nested and adjacent fields. Habitats used included corn and soybean fields, grasslands, and wetlands. Our results suggest that the fledgling period is a critical stage for Dickcissels and that fledglings require habitat similar to habitat used for nesting. Supervivencia Durante el Período Posterior al Emplumamiento en Spiza americana: Implicancias para el Manejo de Hábitat y Conservación

Harvesting Data from Genetically Engineered Crops

More than a billion acres have been planted with genetically engineered crops in the USA since 1996, but we do not fully know their ecological costs and benefits.

Comparison of butterfly communities and abundances between marginal grasslands and conservation lands in the eastern Great Plains

AbstractThe alteration and fragmentation of native tallgrass prairie in the Midwestern United States has created a need to identify other land types with the ability to support grassland butterfly species. This study examines butterfly usage of marginal grasslands, which consist of semi-natural grasslands existing within in a larger agricultural matrix, compared to grasslands managed for conservation of prairie species. Using generalized linear mixed models we analyzed how land purpose (marginal vs. conservation grasslands) affected butterfly abundance. We found grassland butterfly species to be significantly more common on conservation grasslands, whereas generalist species were significantly more common on marginal grasslands. Results of ordination analyses indicated that while many species used both types of habitats, butterfly species assemblages were distinct between habitat types and that edge to interior ratio and the floristic quality index of sites were important habitat characteristics driving this distinction. Within conservation grasslands we examined the relationship between butterfly abundance and the planting diversity used in restoring each site. We found higher diversity restorations hosted more individuals of butterflies considered habitat generalists, as well as species considered to be of conservation concern.

Snakes are Important Nest Predators of Dickcissels in an Agricultural Landscape

Abstract We used video cameras to monitor 33 Dickcissel (Spiza americana) nests during 2003–2004 in the highly-fragmented, agricultural ecosystem of eastern Nebraska and western Iowa. Nine nests fledged young, 20 were completely depredated, three were partially depredated, and one was abandoned due to ants. Nine snakes, six small mammals, six common raccoons (Procyon lotor), two Brown-headed Cowbirds (Molothrus ater), and one American mink (Neovison vison) were documented as nest predators. These results suggest a diversity of predators is responsible for depredation of Dickcissel nests with snake predation being an important cause of nest failure.