FIELD HOST RANGE, FORAGING DEPTH, AND IMPACT OF CRICOTOPUS LEBETIS SUBLETTE (DIPTERA: CHIRONOMIDAE), A BIOLOGICAL CONTROL AGENT OF HYDRILLA VERTICILLATA (L.F.) ROYLE (HYDROCHARITACEAE) By EUTYCHUS MUKURE KARIUKI A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2017 © 2017 Eutychus Mukure Kariuki To my loving family ACKNOWLEDGMENTS I would like to thank my Major Advisor, Dr. Raymond L. Hix, and my Co-Advisor, Dr. James P. Cuda, for their support and guidance during my Ph.D. program. I am also thankful to my committee members, Dr. Stephen D. Hight for his invaluable support and mentorship during the course of my research; Dr. Jennifer Gillett-Kaufman for her constant support, especially through the writing process of my dissertation; and Dr. Lyn Gettys for always being available to help with questions. I am grateful to all others who provided their assistance, including Dr. Edzard van Santen (University of Florida), Dr. Lazarus Mramba (University of Florida), Dr. Emma Weeks (University of Florida), John Mass (United States Department of Agriculture (USDA), Tallahassee, Florida), Kelle Sullivan (Florida Fish and Wildlife Conservation Commission), Dr. Lamberth Kanga (Florida A&M University), and Dr. Muhammad Haseeb (Florida A&M University). I am thankful to all my colleagues and lab mates at the University of Florida who reviewed this manuscript and offered valuable comments and suggestions. I am equally thankful to the USDA for providing funding to this study through the Hydrilla Integrated Pest Management Risk Avoidance and Mitigation Project (IPM RAMP) grant 2010-02825 and the National Institute of Food and Agriculture Crop Protection and Pest Management (NIFA CPPM) grant 2014-70006-22517. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 8 LIST OF FIGURES ........................................................................................................ 10 LIST OF ABBREVIATIONS ........................................................................................... 13 ABSTRACT ................................................................................................................... 14 CHAPTER 1 LITERATURE REVIEW .......................................................................................... 16 Hydrilla .................................................................................................................... 16 Origin and Invasion History of Hydrilla ............................................................. 16 Distribution of Hydrilla in the United States ...................................................... 17 Description of Hydrilla ...................................................................................... 18 Adaptations of Hydrilla...................................................................................... 19 Importance of Hydrilla ...................................................................................... 23 Ecological damage ..................................................................................... 23 Economic damage ..................................................................................... 25 Potential benefits ....................................................................................... 25 Summary.................................................................................................... 27 Management of Hydrilla.................................................................................... 27 Chemical control ........................................................................................ 27 Mechanical control ..................................................................................... 30 Biological control ........................................................................................ 30 History, Benefits, and Approaches of Biological Control of Aquatic Weeds ............ 35 Cricotopus lebetis as a Biological Control Agent of Hydrilla .................................... 37 Background ...................................................................................................... 37 Description ....................................................................................................... 38 Distribution ....................................................................................................... 39 Biology and Feeding Damage .......................................................................... 39 Host Range ...................................................................................................... 41 Need for Research .................................................................................................. 42 2 FIELD HOST SPECIFICITY OF A POTENTIAL HYDRILLA BIOLOGICAL CONTROL AGENT, CRICOTOPUS LEBETIS SUBLETTE (DIPTERA: CHIRONOMIDAE) IN LAKE ISTOKPOGA, FLORIDA ............................................ 49 Introduction ............................................................................................................. 49 Materials and Methods ............................................................................................ 51 Study Area ........................................................................................................ 51 5 Sampling .......................................................................................................... 51 Plant Sample Processing ................................................................................. 53 Cricotopus lebetis Rearing ............................................................................... 53 Data Analysis ................................................................................................... 54 Results .................................................................................................................... 54 Discussion .............................................................................................................. 55 3 ASSESSMENT OF MAXIMUM WATER DEPTH CRICOTOPUS LEBETIS SUBLETTE LARVAE CAN LOCATE HYDRILLA VERTICILLATA (L.F.) ROYLE ... 66 Introduction ............................................................................................................. 66 Materials and Methods ............................................................................................ 69 Greenhouse Experiments ................................................................................. 69 Experiment I: Inoculation of neonate Cricotopus lebetis on the water surface .................................................................................................... 72 Experiment II: Inoculation of Cricotopus lebetis egg masses on the water surface .......................................................................................... 73 Data collection ........................................................................................... 73 Data analyses ............................................................................................ 74 Field Experiments ............................................................................................. 74 Experiment I: Use of sentinel stems to determine the vertical foraging depth of Cricotopus lebetis ..................................................................... 75 Experiment II: Survey of naturally growing stems to determine the vertical foraging range of Cricotopus lebetis ........................................... 75 Data collection ........................................................................................... 76 Data analyses ............................................................................................ 76 Results .................................................................................................................... 77 Greenhouse Experiments ................................................................................. 77 Experiment I: Inoculation of neonate Cricotopus lebetis on the water surface .................................................................................................... 77 Experiment II: Inoculation of Cricotopus lebetis egg masses on the water surface .......................................................................................... 78 Field Experiments ............................................................................................. 79 Experiment I: Use of sentinel stems to determine the vertical foraging range of Cricotopus lebetis ..................................................................... 79 Experiment II: Survey of naturally growing stems to determine the vertical foraging range of Cricotopus lebetis ........................................... 79 Discussion .............................................................................................................. 80 4 COMPETITIVE INTERACTIONS BETWEEN HYDRILLA VERTICILLATA AND THE NATIVE VALLISNERIA AMERICANA AS INFLUENCED BY CRICOTOPUS LEBETIS ........................................................................................ 97 Introduction ............................................................................................................. 97 Materials and Methods .........................................................................................