View of the Hypotheses Describing Mechanisms of Native Coccinellid Decline
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Testing an Interference Competition Hypothesis to Explain the Decline of the Convergent Lady Beetle, Hippodamia convergens (Coleoptera: Coccinellidae), in Ohio. THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Chelsea Smith Graduate Program in Entomology The Ohio State University 2012 Master's Examination Committee: Mary Gardiner, Adviser John Cardina Daniel A. Herms Andrew Michel Copyrighted by Chelsea Ann Smith 2012 Abstract A significant decline in the abundance of the native coccinellid, Hippodamia convergens, coincides with the establishment and population increase of exotic coccinellids in Ohio. This pattern has lead to the hypothesis that intraguild predation by exotic lady beetles explains this decline. Intraguild predation (IGP) is the act of two species, which share a limiting resource, preying on each other. Several laboratory experiments demonstrating the propensity of exotic lady beetles to act as predators of native coccinellid eggs provide support for this hypothesis. The goal of this research was to determine the extent that exotic lady beetles predate on native coccinellid egg masses in the field. Two studies conducted over the course of three field seasons (2009-11), are presented in Chapters 2 and 3 of this thesis. Chapter 2 examines the extent of predation on coccinellid egg masses, and the role of coccinellids as egg predators. The objectives were to 1) compare the extent of egg predation experienced by three coccinellid species: H. convergens, Coleomegilla maculata, and Harmonia axyridis; 2) examine the levels of egg predation occurring across three habitats; and 3) determine the guild of predators responsible for coccinellid egg predation. To address these objectives, egg predation experiments were conducted in habitats where coccinellids are commonly found foraging: grassland, alfalfa, and ii soybean. Eggs of each focal coccinellid species were placed in the fields for 48 hours. The proportion of eggs remaining was compared among lady beetle species and the habitats. Egg masses from the increasingly-rare native lady beetle, H. convergens, incurred significantly greater predation than eggs from the common exotic lady beetle, H. axyridis. Predation of the egg masses from the three species varied across habitats with the greatest amount of predation occurring in grasslands and the least in the alfalfa. These egg predation experiments provided supporting evidence for the IGP hypothesis. Video surveillance systems were placed in the field and focused on coccinellid egg masses. These preliminary video experiments provided evidence that exotic coccinellids were not common predators of the egg masses. Chapter 3 details video experiments conducted to determine patterns among the guild of predators contributing to coccinellid egg predation. The objectives of this study were to 1) measure the relative abundance and activity density of coccinellid egg predators present within grasslands, alfalfa and soybean fields across Ohio; 2) document the contribution of predator species to native and exotic lady beetle egg predation within each foraging habitat; and 3) determine if the relative abundance of aphids affects the intensity of egg predation experienced by lady beetle egg masses. To address these objectives, video surveillance systems were used to observe predation of H. convergens and H. axyridis egg masses in soybean, alfalfa, and grassland habitats. The relative abundance and activity density of aphids and egg predators was also determined using quadrat sampling, sweep samples, and pitfall traps. From the video observations, the guild of egg predators detected included Stylommatophora, Opiliones, Oniscidea, iii Coccinellidae, Gryllidae, Neuroptera, Tettigoniidae, Acrididae, Formicidae, Nabidae, Thripidae, Syrphidae, Araneae, Staphylinidae, and Diplopoda. This guild varied in diversity across the habitats, with the greatest diversity found within grassland habitats. Redundancy analysis revealed two egg predators that maintained a constant pattern of predation across both 2010 and 2011: Formicidae and Oniscidea. These findings indicate that exotic lady beetles are not a significant predator of native coccinellid egg masses within the systems studied. iv Dedicated to my Mother and Father v Acknowledgments I sincerely thank my adviser, Dr. Mary M. Gardiner, for her guidance, encouragement, and constant support throughout my graduate program. Her dedication and sense of humor gave me the drive to work hard on this research and have fun in the process. I also thank my committee members, Dr. John Cardina, Dr. Daniel Herms and, Dr. Andrew Michel for their invaluable advice, support, and a continued interest in this study. I thank all of the OSU extension educators who took the time to show me field sites for this study. Without their relationships with the growers and land owners, finding suitable field sites would have been incredibly difficult. I am also pleased to thank the grower collaborators and land owners who graciously granted me permission to carry out my study in their fields. I thank the present and past members of the Agriculture Landscape Ecology (ALE) lab, Alfred Alumai, Nita Chavez, Ethan Doherty, Hilary Edgington, Kelsey Greathouse, Scott Harrison, Kara Henn, Bethany Hunt, Kathleen Jackson, Andrea Kautz, Ian McIlvaine, Ben Phillips, Jared Power, Scott Prajzner, Shawn Probst, John Roberts, and Steve Ryan, who provided valuable technical and field support as well as wonderful friendships. I also thank Liz Kolbe who donated her time help me collect samples from my field sites. vi I thank Dr. Matt Grieshop, of Michigan State University, who provided the instructions and advice necessary to construct the surveillance camera systems used in this research. Also, I thank Steve Scott for giving his time and expertise to construct the camera systems. I thank Dr. Steve Naber who answered many questions about statistics. I thank Dr. Luis Cañas, the graduate studies committee chair, for his assistance, advice, and patience as I completed the qualifications necessary for earning a Master’s of Science degree though the Department of Entomology. I am also pleased to thank Lori Jones and Brenda Franks for their constant support, assistance, and for answering my various questions about administrative and financial issues. I thank my family who provided unconditional love and support as I accomplished this research, and a very special thanks to my mother, Colleen, and father, Marty, who have always encouraged my education. Thanks are also extended to all of my colleagues who took part in the intellectual conversations during Dollar Beer Wednesdays. This research would not have been possible without funding. Thank you OARDC – SEEDS for financial support of this project. vii Vita 2005................................................................Berkley High School, MI 2009................................................................B.A. Biology, Albion College 2010 to present ..............................................Graduate Research Associate, Department of Entomology, The Ohio State University Fields of Study Major Field: Entomology viii Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. vi Vita ................................................................................................................................... viii Table of Contents ............................................................................................................... ix List of Tables .................................................................................................................... xii List of Figures .................................................................................................................. xiv Chapter 1: A review of the hypotheses describing mechanisms of native coccinellid decline ................................................................................................................................. 1 Introduction ..................................................................................................................... 1 Research Objectives ........................................................................................................ 3 Biology and Ecology of Coccinellidae............................................................................ 5 Biological Control ........................................................................................................... 6 Establishment of Exotics and the Decline of Native Coccinellids .................................. 7 Interference Competition via Intraguild Predation........................................................ 10 Conclusions and Implications of Thesis Research ........................................................ 12 ix References ..................................................................................................................... 14 Chapter 2: Native coccinellids experience greater egg predation than the common exotic Harmonia axyridis in Ohio croplands and grasslands. ..................................................... 19 Abstract ........................................................................................................................