- Agronomic: cotton, rye
- Crop Production: conservation tillage, cover crops, foliar feeding, no-till, nutrient cycling
- Natural Resources/Environment: biodiversity, soil stabilization
- Pest Management: biological control, competition, weather monitoring
- Soil Management: organic matter, soil analysis
Plant- and ground-active arthropods were surveyed over two years from a two-acre cotton farm in Athens, GA supporting whole plot treatments of conventional- (CT) and no-tillage (NT) with subplot treatments of Bt and non-Bt cotton and a winter cover crop of rye or clover. Although neither Bt cotton nor its residue affected total abundance, richness or diversity, three families were significantly affected. Conversely, richness and diversity of non-target arthropods were both significantly higher in NT than in CT plots and a clover cover crop supported higher levels of abundance, richness and diversity during 2005. An interaction was detected between cover crop and cotton residue type with higher abundance, richness and diversity occurring in clover plots with Bt cotton residue than in clover plots with non-Bt residue. Arthropods contributing to significant differences at the community level include plant- and soil surface-active predators, detritivores, pollen feeders, and non-target herbivores. While this study demonstrates slight variations in the impact of Bt cotton under various agricultural management schemes it also reveals that cotton type is the least important factor shaping non-target arthropod communities relative to the other management strategies employed at this particular site.
The effects of genetically modified crops on non-target organisms have been the topic of much recent research, particularly crops modified to express toxins of the bacterium Bacillus thuringiensis Berliner (Bt) (O'Callaghan et al. 2005). The potential effects include toxicity of pest species to their natural enemies due to secondary ingestion of the Bt endotoxin, loss of prey/hosts for predators/parasitoids, decreased prey/host suitability due to endotoxin effects, and effects on soil meso- and macrofauna due to ingestion of either decomposing transgenic plant material or root-exuded endotoxins. O’Callaghan et al. (2005) report that results from both laboratory and field studies reveal mixed effects of Bt cotton on non-target arthropods. This suggests that if Bt cotton does affect non-target arthropods, the impact may be both subtle and context specific.
Most studies addressing the effects of Bt crops on non-target arthropods are limited to simple comparisons between Bt and non-Bt crops. Given the mixed nature of results from past experiments, an examination of the effects of Bt cotton relative to other important agronomic factors that shape arthropod communities may shed light on the true ecological impact of these crops in the context of the overall cropping system. Beyond the context of simple experiments, Bt crops are grown in a complex landscape matrix of agronomic management strategies that include variation in tillage regimes and in cover crops. To begin addressing potential interactions among crop choices and management strategies, I examined the relative contributions of tillage and cover crops to the foliar and ground-dwelling arthropod communities in Bt and non-Bt cotton fields.
The purpose of this study is to compare the effects of Bt and non-Bt cotton on the arthropod communities that are active on plants and at the soil surface as a function of the tillage and cover crop practices in which the respective crops are embedded. By doing so, we can assess context-specific effects of the cotton types on the communities.
I tested the following hypothesize:
H1 – tillage and cover crop type will exert much more influence on arthropod abundance, richness and diversity than will the use of Bt cotton
H2 – tillage and cover crop strategy will not significantly alter the effect of cotton type on arthropod abundance, richness or diversity