ARTHROPOD BIODIVERSITY IN A GEORGIA COTTON AGROECOSYSTEM: THE ROLE OF BT COTTON, TILLAGE, COVER CROPS AND RED IMPORTED FIRE ANTS by KYLE WICKINGS (Under the Direction of John Ruberson) 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. KEY WORDS: Bacillus thuringiensis, tillage, cover crops, Solenopsis invicta, cotton, arthropods, soil ecology, egg predation ARTHROPOD BIODIVERSITY IN A GEORGIA COTTON AGROECOSYSTEM: THE ROLE OF BT COTTON, TILLAGE, COVER CROPS AND RED IMPORTED FIRE ANTS by KYLE WICKINGS B.S., The State University of Buffalo, 2001 A Dissertation Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY ATHENS, GEORGIA 2007 © 2007 Kyle G. Wickings All Rights Reserved ARTHROPOD BIODIVERSITY IN A GEORGIA COTTON AGROECOSYSTEM: THE ROLE OF BT COTTON, TILLAGE, COVER CROPS AND RED IMPORTED FIRE ANTS by KYLE WICKINGS Major Professor: John Ruberson Committee: Mark Hunter Dave Coleman Mark Bradford Paul Hendrix Joseph McHugh Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia December 2007 ACKNOWLEDGEMENTS Many people have assisted me over the course of my dissertation research. I would like to begin by thanking my major advisor John Ruberson. John has been an excellent mentor and his ability to function equally well in both applied and theoretical entomology is a skill that I hope to attain in my academic career. I was also fortunate to work under Mark Hunter during my graduate degree. Mark’s ability to keep the smallest task connected to the big ecological picture is rare, and is something that I have benefited from tremendously. I would also like to thank the rest my graduate committee members; Joseph McHugh, Dave Coleman, Paul Hendrix and Mark Bradford. Their expertise in systematics as well as community, ecosystem and soil ecology provided all of the necessary ingredients for addressing the ecological questions involved in my dissertation research. I’d also like to thank the organizers and instructors of the Ohio State University, Summer Acarology Course and the HYM course for parasitic Hymenoptera. I would also like to thank Ben Mullinix, of the University of Georgia, Coastal Plain Experiment Station for his help in statistical analysis of my data. Finally, I want to thank my parents and my wife Heather. My parents went to great lengths to encourage my interest in the natural world, and my decision to pursue a career in ecology stems directly from this encouragement. Aside from fire ants and maybe okra, I’m now convinced that there is nothing my wife Heather can’t handle. She has provided unwavering support for me during my graduate degree and has adapted to every situation I’ve dragged her into better than I ever could. iv TABLE OF CONTENTS Page ACKNOWLEDGMENTS ............................................................................................................. iv LIST OF TABLES......................................................................................................................... vi LIST OF FIGURES ..................................................................................................................... viii CHAPTERS 1 INTRODUCTION AND LITERATURE REVIEW ........................................................1 2 THE EFFECT OF TRANSGENIC BT COTTON ON ARTHROPOD COMMUNITIES UNDER VARYING TILLAGE AND COVER CROPPING PRACTICES...............32 3 IMPACT OF THE RED IMPORTED FIRE ANT (SOLENOPSIS INVICTA) ON SOIL ARTHROPOD COMMUNITIES OF COTTON AGROECOSYSTEMS ..................74 4 EGG PREDATION BY THE RED IMPORTED FIRE ANT, SOLENOPSIS INVICTA, ON FOLIAGE AND AT THE SOIL SURFACE OF A COTTON AGROECOSYSTEM ................................................................................................119 5 CONCLUSIONS AND FUTURE DIRECTIONS........................................................160 v LIST OF TABLES Page Table 2.1: Sampling schedule and planting dates .........................................................................52 Table 2.2a: Mean abundance richness and diversity (October 2004 and 2005) ............................53 Table 2.2b: Mean abundance richness and diversity (April 2004 and 2005) ................................54 Table 2.3: Two-way interactions (tillage x cover crop).................................................................55 Table 2.4: Two-way interactions (tillage x cotton)........................................................................56 Table 2.5: Two-way interactions (tillage x cotton residue) ...........................................................57 Table 2.6: Two-way interactions (tillage x cover crop residue) ....................................................58 Table 2.7: Two-way interactions (cover crop x cotton residue) ....................................................59 Table 2.8: Two-way interactions (cotton x cover crop residue) ....................................................60 Table 2.9: Three-way interactions (April 2004 and 2005) ............................................................61 Table 2.10: Three-way interactions (October 2004 and 2005)......................................................63 Table 3.1: Fire ant exclusion efficacy test (Coastal Plain Experiment Station 2007) ...................97 Table 3.2: List of taxa collected from pitfall traps (2006 and 2007) .............................................99 Table 3.3: List of taxa collected from soil core heat extraction (2006 and 2007) .......................101 Table 3.4: Mean abundance, richness and diversity (pitfall traps 2006) .....................................102 Table 3.5: Mean percentages of major groups between fire ant inclusion and exclusion plots (pitfall traps 2006)......................................................................................................103 Table 3.6: Mean abundance, richness and diversity (pitfall traps 2007) .....................................104 Table 3.7: Mean abundance, richness and diversity (soil core heat extraction 2006) .................105 vi Table 3.8: Mean percentages of major groups between fire ant inclusion and exclusion plots (soil core heat extraction 2006)..........................................................................................106 Table 3.9: Mean abundance, richness and diversity (soil core heat extraction 2007) .................107 Table 4.1: Fire ant exclusion efficacy test (Coastal Plain Experiment Station 2007) .................143 Table 4.2: Mean proportion of Nezara viridula eggs removed from fire ant inclusion and exclusion plots ...........................................................................................................144 vii LIST OF FIGURES Page Figure 2.1: LS mean differences in abundance between cotton type (October 2005)...................65 Figure 2.2: LS mean differences in abundance between cotton residue type (April 2004)...........66 Figure 2.3: LS mean differences in abundance between tillage type (April 2004 and 2005)........67 Figure 2.4: LS mean differences in abundance between tillage type (October 2004 and 2005) ...69 Figure 2.5: LS mean differences in abundance between cover crop type (April 2005) ................71 Figure 2.6: Mean abundance, richness and diversity (cover crop x cotton residue, April 2004) ..72