Epigeal insect diversity and dynamics in agroecosystems adopting transgenic crops
Open Access
- Author:
- Leslie, Timothy William
- Graduate Program:
- Entomology
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 28, 2007
- Committee Members:
- Shelby Jay Fleischer, Committee Chair/Co-Chair
Mary Ellen Barbercheck, Committee Member
David Biddinger, Committee Member
David A Mortensen, Committee Member - Keywords:
- Carabidae
genetically modified crops
ordination
Bt crops
non-target effects
Staphylinidae - Abstract:
- Using data from five years of field experiments, we assessed the influence of insecticidal transgenic crop technologies on non-target epigeal insect diversity in both maize and diversified vegetable agroecosystems. Concurrently, we considered the relative influence of crop species, crop rotations, and proximity to forested field margins on these insect communities. Our approach differed from other transgenic non-target studies by emphasizing species-level identification of a functionally diverse subset of the epigeal insect community, notably Coleoptera, with extensive analysis of Carabidae, to maximize the biological and functional resolution of the data. We examined population dynamics as well as community response using current statistical approaches in the fields of biodiversity sciences and community ecology. Insecticide inputs were lower in transgenic crops due to the efficient control of important pest taxa, which served to sustain epigeal biodiversity. In maize agroecosystems, no differences were found between the coleopteran communities in conventional and transgenic insect control practices where transgenic field corn contained a neonicotinoid seed treatment. Both management tactics negatively influenced coleopeteran communities compared to a control. Dominant members of the carabid community exhibited temporal partitioning of resources. One species, Harpalus pensylvanicus, consistently exhibited higher activity-densities in the control fields, and was identified as a possible bio-indicator. Despite management influences, differences between crop species and the effect of crop rotations was often sufficient to mask any treatment effects. Carabid communities were significantly different between maize and a forested field margin, and shifts in community structure along a transect were most rapid at the grassy margin between the two habitats. Carabidae communities were more diverse in the forest edge, where plant diversity was also highest. Despite strong habitat associations, most abundant carabids were found in both forest and maize. Differences between carabid communities in maize fields at varying distances from a forested margin suggested landscape level influences. In conclusion, the spatial and temporal heterogeneity of agroecosystems in the northeastern U.S. seemed to promote on-farm insect diversity, although non-target effects from transgenics coupled with neonicotinoid seed treatments and conventional insect control methods were discernible from a control.