INTERACTIVE EFFECTS OF GEOGRAPHY AND HOST PLANT SPECIES ON GENETIC AND PHENOTYPIC VARIATION OF COTTON FLEAHOPPER POPULATIONS A Dissertation by APURBA KUMAR BARMAN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY December 2011 Major Subject: Entomology INTERACTIVE EFFECTS OF GEOGRAPHY AND HOST PLANT SPECIES ON GENETIC AND PHENOTYPIC VARIATION OF COTTON FLEAHOPPER POPULATIONS A Dissertation by APURBA KUMAR BARMAN Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Approved by: Co-chairs of the Committee, Raul F. Medina Megha N. Parajulee Committee Members, Chris Sansone Adam G. Jones Charles P. C. Suh Head of Department, David Ragsdale December 2011 Major Subject: Entomology iii ABSTRACT Interactive Effects of Geography and Host Plant Species on Genetic and Phenotypic Variation of Cotton Fleahopper Populations. (December 2011) Apurba Kumar Barman, B.Sc., M.Sc., Assam Agricultural University; M.S., Texas Tech University Co-Chairs of Advisory Committee: Dr. Raul F. Medina Dr. Megha N. Parajulee The cotton fleahopper, Pseudatomoscelis seriatus (Reuter) is a widely distributed insect across the United States. Although, it feeds on several native wild hosts, its agricultural importance lies as an economic pest of cotton in several states in the southern United States. No studies have addressed intraspecific genetic and phenotypic variation of this insect pest at a large geographic scale. I examined genetic variation among cotton fleahopper populations associated with cotton in different geographic locations across the southern United States (Chapter II). Using dominant, neutral, nuclear molecular markers (AFLP, amplified fragment length polymorphism) and mitochondrial DNA sequences, I found that overall genetic differentiation among different geographic populations, collected from cotton in eleven cotton growing states, was low but significant. AFLP revealed the presence of three regional groups representing western (Arizona), central (Texas, Oklahoma, Arkansas, Louisiana, Mississippi and Alabama), and eastern (Florida, Georgia, South Carolina and North Carolina) populations. iv I examined if there were distinct lineages of cotton fleahoppers associated with three of its host plant species: cotton (Gossypium hirsutum), horsemint (Monarda punctata) and woolly croton (Croton capitatus) in five different locations of Texas by using AFLP markers (Chapter III). I found two distinct host-associated lineages at three locations and local panmixia in the other two locations. I tested if host preference of cotton fleahoppers were affected by geographic variation and prior experience. Conducting choice tests with a Y-tube olfactometer, I found that host preference in cotton fleahoppers for horsemint (one of its native host plants) is conserved and unaffected by individual‟s prior experience with cotton (Chapter IV). Finally, I explored the role of host-plant species in morphological differentiation of the cotton fleahopper in two locations that differ in presence of distinct host- associated lineages. Using a geometric-morphometric approach, I detected significant effect of host plant and geography on body morphology and wing shape of cotton fleahopper populations (Chapter V). Length of antenna and rostrum were two important traits associated with morphological divergence of cotton and horsemint associated insect populations. Cotton associated individuals had relatively longer antenna and rostrum compared to individuals associated with horsemint. v ACKNOWLEDGEMENTS I offer my sincere gratitude to all my committee members (Drs. Raul Medina, Megha Parajulee, Chris Sansone, Adam Jones and Charles Suh) who have advised, critiqued, and supported my Ph.D. dissertation research. All of you have contributed towards successful completion of my degree program and I duly acknowledge your time and involvement. I will remember Dr. Medina‟s relentless effort in reading and suggesting corrections of my writings for the last several years. You have also given me enough independence to explore and execute my research questions, which of course sometime might have led me to distractions. I must say that Dr. Parajulee has trusted me enough and kept me associated with him for the past 7+ years. Without your help and inspiration, it would have been difficult for me to reach the status in which I find myself today. The financial supports from Texas AgriLife Research and Extension, Plains Cotton Growers Inc., Cotton Incorporated, Texas State Support Committee, Texas A&M University, and Texas EcoLab made this body of research possible. I sincerely acknowledge your investments. Dr. Suh was highly instrumental in giving my research a „jump start‟ with his knowledge on cotton fleahopper biology and habitat. I am grateful to Adam Jones, Department of Biology, who advised me in the area of evolutionary biology and pointed me in to the right direction. I acknowledge the collaboration with Dr. Tomas DeWitt, Dept. of Wildlife and Fishery Sciences, which expanded the scope of my study on morphological differentiation. vi Here, I extend my appreciation to Dr. John Westbrook, USDA-ARS, APMRU for his cooperation and logistic help. Drs. Scott Armstrong, Roy Parker, Terry Pitts (Oklahoma) and Peter Ellsworth (Arizona) generously provided cotton fleahopper samples. I extend my thankfulness to the Cotton Entomology Program at the Lubbock AgriLife Research Center and Dr. Ram Shrestha. I am thankful to Drs. Micky Eubanks and Michel Slotman for allowing me to use their laboratory space on several occasions. I really appreciate the friendship of Kevin Deitz, who helped me in part of my research. I visited a number of places not only in Texas but also in several other states and sampled cotton fields without knowing the farmer‟s name or address. In all my good intensions, two persons always watched my back: my friend, Stanley Carroll and my wife, Babi. I express my heartiest gratitude to their patience, love, and encouragement. Several years of living experience in Bryan-College Station, fascinating Aggieland, my academic department (entomology), and many good friends, all were stimulating to the success of my degree program. I gratefully acknowledge the friendship, help, and cooperation from my friends in the Medina-Lab: Aaron, Emilie, Andrea, Mauro, Suhas, Josephine, Steven, Luke (NSF-REU) and Kyle. I express my gratitude to my family and friends in this country: Mark Arnold (Lubbock, TX), Evelyn Bernard (El Paso, TX), Venkat Parkunan (Tifton, GA), and Parajulee-family (Lubbock. TX), who inspired and supported my life and endeavors in several ways. Finally, I convey my sincere thanks and regards to my two pairs of parents and other family members who wished, cared and prayed for my success and conclusion of my doctoral degree. vii TABLE OF CONTENTS Page ABSTRACT .............................................................................................................. iii ACKNOWLEDGEMENTS……………………………………………………….. v TABLE OF CONTENTS .......................................................................................... vii LIST OF FIGURES ................................................................................................... ix LIST OF TABLES .................................................................................................... xi CHAPTER I INTRODUCTION ................................................................................ 1 II GEOGRAPHIC STRUCTURE OF GENETIC VARIATION OF COTTON FLEAHOPPER, Pseudatomoscelis seriatus POPULATIONS IN THE UNITED STATES……………………….. 7 Introduction .................................................................................... 7 Materials and methods ................................................................... 11 Results ............................................................................................ 16 Discussion ...................................................................................... 29 III GEOGRAPHIC PATTERN OF HOST-ASSOCIATED DIFFERENTIATION IN THE COTTON FLEAHOPPER, Pseudatomoscelis seriatus (Reuter)…………………………………. 36 Introduction .................................................................................... 36 Materials and methods ................................................................... 38 Results ............................................................................................ 47 Discussion ...................................................................................... 57 viii CHAPTER Page IV HOST PREFERENCE OF COTTON FLEAHOPPER, Pseudatomoscelis seriatus (Reuter) IS NOT LABILE TO GEOGRAPHIC ORIGIN AND PRIOR EXPERIENCE…………… 62 Introduction .................................................................................... 62 Materials and methods ................................................................... 65 Results ............................................................................................ 71 Discussion ...................................................................................... 74 V MORPHOLOGICAL VARIATION IN COTTON FLEAHOPPER POPULATIONS: GEOMETRIC MORPHOMETRIC APPROACHES TO QUANTIFY THE INTERACTIVE EFFECT OF HOST PLANT AND GEOGRAPHY 79 Introduction ................................................................................... 79 Materials and methods ..................................................................