Arthropod biodiversity in a Georgia cotton agroecosystem
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Genetically modified (GM) crops and invasive species have been extensively studied in the field of agroecology, particularly for their effects on biodiversity. While studies examining GM crops have found very little evidence that these crops negatively affect arthropod communities, they have not taken into account the various agricultural management strategies within which they are nested. Due to the frequent disturbance inherent in agricultural production, invasive species are common members of arthropod communities in agroecosystems. Invasives can have both positive and negative impacts on arthropod communities within these systems; however, there are many areas in which their influence has not been adequately assessed. In the chapters that follow I first examine the effects of genetically modified, Bt cotton on non-target arthropod communities relative to and in combination with the effects of tillage and cover crop identity. While Bt cotton appeared to have subtle effects on a few taxa, they were minor and inconsistent compared to and in combination with the effects of tillage and cover crop type. Next I assess the impact of the red imported fire ant Solenopsis invicta on arthropods both at and below the soil surface. The removal of fire ants significantly altered the abundance of certain arthropod families. Many of the same trophic groups were affected at two field sites, but the abundance of these groups did not always respond in the same direction. Potential mechanisms leading to the differences detected between field sites, including weed density and arthropod species-specific responses, are further discussed. Finally, I examine the contribution of the red imported fire ant, Solenopsis invicta on egg predation rates in a cotton agroecosystem. Fire ants contributed greatly to predation of eggs of the beet armyworm, Spodoptera exigua, both on cotton foliage and at the soil surface. While fire ants also contributed significantly to predation of eggs of the southern green stink bug, Nezara viridula, in cotton foliage, they ignored eggs of the redbanded stink bug Piezodorus guildinii. This study also suggests that whitefly densities on cotton foliage may significantly influence egg removal rates of N. viridula eggs by fire ants.