SEASONAL CHANGES IN HOST USE AND VECTORIAL CAPACITY OF Culiseta melanura (Diptera: Culicidae) IN RELATION TO EPIZOOTIC TRANSMISSION OF EASTERN EQUINE ENCEPHALITIS VIRUS IN CENTRAL FLORIDA By RICHARD G. WEST A THESIS PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE UNIVERSITY OF FLORIDA 2019 © 2019 Richard G. West 2 ACKNOWLEDGMENTS I would like to thank my advisor Nathan Burkett-Cadena for his invaluable guidance and instruction and Derrick Mathias and Jonathan Day for serving on my committee and sharing their expertise and helpful input. I would like to thank the following for their assistance with mosquito sampling: Carl Boohene, Jackson Mosley, Hugo Ortiz Saavedra, and Roger Johnson at Polk County Mosquito Control District; Kelly Deutsch, Rafael Melendez, and others at Orange County Mosquito Control District; and Sue Bartlett, Miranda Tressler, Hong Chen, Drake Falcon, Tia Vasconcellos, and Brandi Anderson at Volusia County Mosquito Control District. This study could not have been done without their cooperation and hard work. I would also like to thank Carolina Acevedo for help with bloodmeal analysis, Erik Blosser for help with mosquito identifications, Diana Rojas and Annsley West for helping with field collections, and to all the faculty, staff, and students at FMEL for their support and encouragement. Finally, I thank my wife Annsley for her faithful encouragement and love and for my Lord Jesus and family for their support. This research is supported by the CDC Southeast Gateway Center of Excellence and the University of Florida. 3 TABLE OF CONTENTS Page ACKNOWLEDGMENTS .................................................................................................. 3 LIST OF TABLES ............................................................................................................ 6 LIST OF FIGURES .......................................................................................................... 7 LIST OF DEFINITIONS AND ABBREVIATIONS ............................................................. 8 ABSTRACT ..................................................................................................................... 9 CHAPTER 1 INTRODUCTION .................................................................................................... 11 Eastern Equine Encephalitis Virus and Culiseta melanura ..................................... 11 Seasonality of EEEV ............................................................................................... 13 2 SEASONAL HOST USE OF Culiseta melanura ..................................................... 15 Materials and Methods............................................................................................ 17 Field Locations ................................................................................................. 17 Mosquito Sampling ........................................................................................... 17 Bloodmeal Analysis .......................................................................................... 18 Results .................................................................................................................... 21 Culiseta melanura Bloodmeals ......................................................................... 21 Seasonal Host Use ........................................................................................... 22 Avian Host Diversity and Residency ................................................................. 23 Mammalian Bloodmeals ................................................................................... 24 Discussion .............................................................................................................. 25 3 SEASONAL CHANGES IN VECTORIAL CAPACITY OF Culiseta melanura FOR EEEV IN CENTRAL FLORIDA ....................................................................... 41 Seasonality of EEEV in Florida ............................................................................... 41 Vectorial Capacity ................................................................................................... 41 Materials and Methods............................................................................................ 46 Parity Determinations ....................................................................................... 46 Vectorial Capacity Calculations ........................................................................ 46 Results .................................................................................................................... 49 Mosquito Abundance and Host Feeding .......................................................... 49 Parity Rate, Gonotrophic Cycle Length, and Extrinsic Incubation Length ........ 49 EEEV Transmission in Central Florida ............................................................. 50 Vectorial Capacity ............................................................................................ 51 Discussion .............................................................................................................. 52 4 Vectorial Capacity ............................................................................................ 52 Abundance ....................................................................................................... 52 Host use ........................................................................................................... 54 Mosquito Survival ............................................................................................. 55 Conclusion ........................................................................................................ 55 LIST OF REFERENCES ............................................................................................... 64 BIOGRAPHICAL SKETCH ............................................................................................ 72 5 LIST OF TABLES Table page 2-1 Collection sites of Cs. melanura in central Florida. ............................................. 30 2-2 Forward and reverse primers used for bloodmeal host identification. ................. 31 2-3 Vertebrate hosts of Cs. melanura by county ....................................................... 32 2-4 Vertebrate hosts of Cs. melanura by month. ...................................................... 34 3-1 Monthly abundance of Cs. melanura and other mosquito species ..................... 57 3-2 Vectorial capacity variables of Cs. melanura for EEEV ...................................... 58 6 LIST OF FIGURES Figure page 2-1 Map of collection sites in central Florida, USA.................................................... 36 2-2 Mosquito resting shelter ..................................................................................... 37 2-3 Aspirator used in mosquito collection from resting shelters ................................ 38 2-4 Seasonal host use by Cs. melanura in central Florida ........................................ 39 2-5 Monthly resident and nonresident bird host detection ........................................ 40 3-1 Ovaries from Cs. melanura at 100X magnification ............................................. 59 3-2 Mean density of Cs. melanura from Orange and Polk County, FL in 2018 ......... 60 3-3 Parity of Cs. melanura from Orange and Polk County, FL in 2018 ..................... 61 3-4 Vectorial capacity (C) of Cs. melanura for EEEV against EEEV equine cases from 2018 and past decade ................................................................................ 62 3-5 Relationship of central Florida EEEV equine cases and vectorial capacity of Cs. melanura ...................................................................................................... 63 7 LIST OF DEFINITIONS AND ABBREVIATIONS Bridge vector A species of arthropod that acquires an infectious agent from an infected wild animal and then transmits the agent to a non- amplifying host. C Vectorial capacity; the average number of new vertebrate infections per day resulting from an initial index case. Dilution host A species that has low host competence for an infectious agent which reduces transmission by decreasing contact between competent vectors and competent hosts. EEEV Eastern equine encephalitis virus. Encephalitis Inflammation of the brain. Endemic Regularly found among particular group or in a certain area. Enzootic In relation to a disease regularly affecting nonhuman animals. Epizootic An outbreak of disease in nonhuman animals; in relation to an epizootic disease in animals. Extrinsic incubation The interval between the acquisition of an infectious agent by a period vector and the point at which the vector is able to transmit the agent to other susceptible vertebrate hosts. Host competence The physiological ability of a host organism to acquire, maintain and transmit an infectious agent. Parity The reproductive state of an organism; whether a female has completed a reproductive cycle. Vector competence The physiological ability of a vector organism to acquire, maintain and transmit an infectious agent. 8 Abstract of Thesis Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Master of Science SEASONAL CHANGES IN HOST USE AND VECTORIAL CAPACITY OF Culiseta melanura (Diptera: Culicidae) IN RELATION TO EPIZOOTIC TRANSMISSION OF EASTERN EQUINE ENCEPHALITIS VIRUS