BT Cotton, Tillage and Cover Crops Identity: Relative Effects on Above and Below Ground Invertebrate Diversity

BT Cotton, Tillage and Cover Crops Identity: Relative Effects on Above and Below Ground Invertebrate Diversity

Summary

This reporting period involved identification of all arthropod samples and data analysis. This is the particular stage during which the microscope and identification manuals noted in my budget were utilized.
All arthropods were identified to the family level. Arthropod communities were analyzed both at the whole-community and individual family level for treatment effects.
Results suggest that the impact of Bt cotton on non-target arthropods is insignificant relative to the impact of tillage and cover crop choice.

Objectives/Performance Targets

Complete identification of all samples followed by analysis of arthropod communities for treatment effects.
Analysis of data using mixed model analysis was initiated to investigate whether or not significant differences existed at the whole- community level. Whole-community parameters included abundance, richness and diversity using the shannon index (H).

Accomplishments/Milestones

All objectives for this term were accomplished. All arthropod samples were processed and identified. Also, all data was analyzed for both whole-community effects and significant differences at the individual family level.

Impacts and Contributions/Outcomes

To date, the results of this project suggest that the impact of Bt cotton on non-target arthropods is insignificant relative to the impacts of tillage strategy and cover crop choice.
Whole-community analyses demonstrate that tillage has a significant impact on arthropod richness and diversity, with both being higher in no-till plots than in conventionally tilled plots. Similarly, cover crop type significantly effects arthropod abundance, richness and diversity. In this experiment, all three were higher in clover than in rye plots. It is important to note however, that this may be largely due to the fact that clover was flowering at the time of sampling. Although cotton type itself had no effect on whole-community parameters, there was a significant interaction effect of cover crop by cotton residue, where arthropod abundance, richness and diversity were each higher in clover plots with Bt cotton residue. This result is difficult to interpret given that there were no differences in either crop or residue biomass between treatments and given that lack of non-target effects of Bt cotton even while plants are living.
Analysis at the individual family level revealed which arthropod families contributed to the significant differences noted at the whole-community level. For the tillage effect noted, the following arthropod taxa were significant indicators of no-till soil management: Formicidae, Grillidae, Sminthuridae, Miridae, Linyphiidae, Oribatidae, Entomobryidae, Prostigmata, Isotomidae and Hypogastruridae.
For the cover crop effect noted, the following arthropod taxa were significant indicators of clover plots: Miridae, Drosophilidae, Apidae, Formicidae, Chironomidae, Cicadellidae, Acrididae, Tenebrionidae, Sciaridae, Nitidulidae and Dolichopodidae.
Finally, for the cover crop by cotton residue interaction, the following arthropod taxa were significant indicators of clover plots with Bt cotton residue: Miridae, Cicadellidae and Oribatida.
To date, this data has been presented in both poster and presentation form. As a poster it was presented at the annual meeting of the Entomological Society of America, December 06, Indianapolis, IN. As a 10 minute presentation these results were presented at the Soil Ecology Program in Wageningen, The Netherlands.

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