THE BERMUDAGRASS STEM MAGGOT: AN EXOTIC PEST IN THE SOUTHEASTERN UNITED STATES by LISA LEANNE BAXTER (Under the Direction of Dennis W. Hancock) ABSTRACT The bermudagrass stem maggot (BSM; Atherigona reversura Villeneuve) has infested and damaged bermudagrass [Cynodon dactylon (L.) Pers.] hayfields throughout the southeastern United States. Eight Cynodon cultivars were tested and it was determined that the number and percent of tillers damaged depends on cultivar, but an average 7.7% decrease in total dry biomass was observed for all cultivars. Unfortunately, there is no information available on the reproductive potential of the BSM. Adult flies dissected from various regions in Georgia and Florida demonstrated that the reproductive morphology resembled A. soccata and the total number of ovarioles varied with region. To provide information on morphological differences among Cynodon cultivars, eight characteristics were compared, and it was concluded that C. dactylon have denser, lighter green, finer-textured canopies while C. nlemfuensis Vanderyst had less leaf density, were darker green, and more robust. Cultivar tolerance appears to be the best IPM strategy to implement for BSM control. INDEX WORDS: Bermudagrass, Cynodon, Bermudagrass Stem Maggot, BSM, Atherigona reversura, cultivar differences, ovariole number THE BERMUDAGRASS STEM MAGGOT: AN EXOTIC PEST IN THE SOUTHEASTERN UNITED STATES by LISA LEANNE BAXTER BS, Berea College, 2012 A Thesis Submitted to the Graduate Faculty of The University of Georgia in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE ATHENS, GEORGIA 2014 © 2014 Lisa Leanne Baxter All Rights Reserved THE BERMUDAGRASS STEM MAGGOT: AN EXOTIC PEST IN THE SOUTHEASTERN UNITED STATES by LISA LEANNE BAXTER Major Professor: Dennis W. Hancock Committee: William G. Hudson William F. Anderson Brian M. Schwartz Electronic Version Approved: Maureen Grasso Dean of the Graduate School The University of Georgia May 2014 iv DEDICATION I dedicate this thesis to my advisors and professors who have guided me through not only my education but also many of life’s important choices. Also, this thesis would not have been possible without the unconditionally support of my closest friends. v ACKNOWLEDGEMENTS I would like to acknowledge my committee and collaborators on this project: Dr. Dennis Hancock (UGA-Athens), Dr. Will Hudson (UGA-Athens), Dr. Brian Schwartz (UGA-Tifton), Dr. Bill Anderson (USDA-ARS Coastal Plains Experiment Station), and Dr. Patricia Moore (UGA-Athens). I would also like to thank all of the producers who invited me to sample for the BSM in their pastures and hayfields and the Cooperative Extension Agents who have coordinated field visits: Tammy Cheely (Warren County, GA), Phillip Edwards (Irwin County, GA), Keith Fielder (Putnam County, GA), Raymond Joyce (Laurens County, GA), Peyton Sapp (Burke County, GA), Elena Toro (Suwannee County, FL), and Tim Varnedore (Jeff Davis County, GA). vi TABLE OF CONTENTS Page ACKNOWLEDGEMENTS .............................................................................................................v LIST OF TABLES ....................................................................................................................... viii LIST OF FIGURES .........................................................................................................................x CHAPTER 1 INTRODUCTION .........................................................................................................1 REFERENCES ........................................................................................................4 2 LITERATURE REVIEW ..............................................................................................9 REFERENCES ......................................................................................................17 3 THE RESPONSE OF SELECTED BERMUDAGRASS CULTIVARS TO BERMUDAGRASS STEM MAGGOT DAMAGE ....................................................25 ABSTRACT ...........................................................................................................26 INTRODUCTION .................................................................................................26 MATERIALS AND METHODS ...........................................................................28 RESULTS AND DISCUSSION ............................................................................33 CONCLUSIONS....................................................................................................37 REFERENCES ......................................................................................................39 4 EXPLORATION OF THE REPRODUCTIVE MORPHOLOGY AND POTENTIAL OF THE BERMUDAGRASS STEM MAGGOT........................................................48 ABSTRACT ...........................................................................................................49 vii INTRODUCTION .................................................................................................49 MATERIALS AND METHODS ...........................................................................52 RESULTS AND DISCUSSION ............................................................................53 CONCLUSIONS....................................................................................................55 REFERENCES ......................................................................................................56 5 MORPHOLOGICAL CHARACTERISTICS OF SELECT CYNODON CULTIVARS ................................................................................................................................64 ABSTRACT ...........................................................................................................65 INTRODUCTION .................................................................................................65 MATERIALS AND METHODS ...........................................................................68 RESULTS AND DISCUSSION ............................................................................70 CONCLUSIONS....................................................................................................72 REFERENCES ......................................................................................................73 6 CONCLUSIONS, IMPLICATIONS, AND FUTURE RESEARCH DIRECTIONS .79 APPENDIX A SELECT TABLES .......................................................................................................83 viii LIST OF TABLES Page Table 2.1: Summary of plant characteristics that reduce Atherigona damage in other field crops…. ..............................................................................................................................24 Table 2.2: Summary of plant compounds found to attract or deter A. soccata..............................24 Table 3.1: Location of field sampling sites ....................................................................................43 Table 3.2: Analysis of variance for the effects and interactions of year, fly treatment, and cultivar on number of tillers, number of infected tillers, and percent of infected tillers pot-1 during a 2-year period. ..................................................................................................................44 Table 3.3: Effect of cultivar on the mean number of tillers pot-1 during a 2-year period. .............44 Table 3.4: Analysis of variance for the effects of year, fly treatment, and cultivar on undamaged, damaged, and total dry weight during a 2-year period. .....................................................45 Table 3.5: Analysis of variance for effects and interactions of year, treatment, and cultivar on phenotypic characteristics over a 2-year period. ................................................................46 Table 3.6: Effect of fly treatment on phenotypic plant characteristics over a 2-year period. ........47 Table 3.7: Analysis of variance for the effects and interaction of yield and cultivar on the mean number of larvae excised pot-1 harvest-1 over a 2-year period. ..........................................47 Table 4.1: Location of field sampling sites. ...................................................................................63 Table 4.2: Analysis of variance for the effect of region on total number of ovarioles and total number of mature oocytes ..................................................................................................63 Table 5.1: Summary of bermudagrass cultivar recommendations for the SE US. ........................76 ix Table 5.2: Analysis of variance for the effects and interaction of year and cultivar on various phenotypic plant characteristics during a 2-year period. ...................................................77 Table 5.3: Effect of cultivar on phenotypic plant characteristics ..................................................78 x LIST OF FIGURES Page Figure 1.1: Large areas of bermudagrass with chlorotic tips indicate the bermudagrass stem maggot may be present, though a more thorough evaluation should be conducted. ...........7 Figure 1.2: An individual shoot that has been damaged by the bermudagrass stem maggot as indicated by the restriction of the chlorosis to the top leaves (a). Damaged leaves that have been easily pulled from the pseudostem (b). Decaying plant material resulting from BSM larva feeding (c) ..........................................................................................................7