CONSERVATION OF INSECT NATURAL ENEMIES IN HETEROGENEOUS VEGETABLE LANDSCAPES DISSERTATION Presented in Partial Fulfillment of the Requirements for The Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Janet Louise Lawrence, M.S. * * * * * The Ohio State University 2004 Dissertation Committee: Approved by Dr. Casey Hoy, Adviser Dr. Clive Edwards Dr. Parwinder Grewal Adviser Dr. Larry Phelan Department of Entomology ABSTRACT The position taken is that populations of natural enemies occupying both soil and foliar habitats are regulated by lower trophic levels. A series of hypotheses were tested on the influence of lower trophic levels on population persistence of natural enemies with divergent life history traits; the entomopathogenic nematode, Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae) and the larval parasitoid, Diadegma insulare Cresson (Hymenoptera: Ichneumonidae). Initial studies on the entomopathogenic nematode, were aimed at understanding their ecology in vegetable landscapes and thereafter investigations were conducted to determine the influences of insect host availability and plant diversity on population densities and the mechanisms underlying their effects. Investigations for D. insulare, focused on its responses to densities of the diamondback moth, Plutella xylostella L. (Lepidoptera: Plutellidae) and flowering coriander. Several strains of entomopathogenic nematodes that were able to infect and reproduce in common vegetable insect pests were recovered along grassy banks adjacent to cultivated areas of a vegetable production system. Soil moisture was the principal factor associated with the presence of these endemic nematode populations. Persistence of H. bacteriophora populations differed in plots with different insect host availability, but persistence differed among strains and was related, in part, to the abilities of the ii nematodes to survive under test site conditions. For those strains with high survival rates, populations increased with increasing host availability, whereas no such effects were observed for populations with low survival rates. Higher nematode population densities were observed in plots with more diverse plants and insect herbivores. A correlation was found between nematode population density and chrysomelid beetle abundance, suggesting that persistence was at least partially as a result of nematodes recycling within these insects. D. insulare aggregated twice as much in areas with high compared with low populations of diamondback moth. Parasitism was greater when flowering coriander was present, but this effect was only observed at low population densities. In summary, bottom-up effects of plant and herbivore communities on natural enemies above and below-ground were similar. Population persistence for the two natural enemies was higher with increasing insect hosts and plant diversity; but the effects occurred at different spatial and temporal scales. iii DEDICATION To my mother, Enid Dorothy Lawrence iv ACKNOWLEDGEMENTS I would like to express my sincere gratitude to my major advisor, Dr Casey Hoy for his guidance in shaping this project, constant support and infinite patience. To have had the opportunity to work with a true mentor and someone whose mind I greatly admire was indeed a privilege. To Dr Clive Edwards, who encouraged me to enroll at the Ohio State University and whose support has been tremendous, especially during my time in Columbus, I am grateful. Special thanks to Dr Larry Phelan for his thought provoking queries that challenged me to think more deeply and clearly about this project. Grateful thanks to Dr Parwinder Grewal, for always taking the time to give suggestions, generously opening his lab facilities to me and reintroducing me to the “tiny creatures” I had left behind years ago. There are really no words to express my gratitude to Mike Dunlap for his logistical support over the years and his friendship. Mike worked tirelessly, to ensure that I had all I needed to execute this project. My appreciation to Dr Mustapha Jallow for his willingness to help with the many field sampling expeditions, Dr Krishna Prasad for assisting with GIS software and Ms Nuris Acosta for taxonomic support. Thanks to the multitude of summer workers that provided youthful exuberance during challenging sampling times, namely: Niccoli Fioritto, Timothy Taush, Joe Dunlap, Benjamin Dunlap, Kyle Kauffman, Kate Williams, Charles Gilbert, Jeshua Cressap, Katie Gerber, and v Jeremy Jewel. Thanks also to Rick Callendar and the field staff of the OARDC Muck Crops Branch for their assistance, in particular during trying times of flooded field plots. Special thanks to: Catherine Herms for constantly being available to help me to understand the workings of the GPS, Bonnie Slovboda for the last minute poster demands and the library staff for their assistance. My deep appreciation to Mabel Kirchner and Shirley Holmes for their encouragement and support. To the many friends who boosted my spirits and helped me to feel at home in Ohio, I am grateful. I would like to thank the Department of Entomology for supporting my graduate education here at The Ohio State University. Appreciation also to the Ohio Vegetable and Small Fruit Research, Ohio Department of Agriculture and United States Department of Agriculture Specialty Crop Block Grant and Development Program for consistently funding our research proposals to execute this work. Finally, I am truly indebted to my mom, Enid and sister, Phillipa who have been my sources of inspiration, encouragement and strength at all times. vi VITA December 11th, 1965……………………………. Born in Kingston, Jamaica 1985 – 1989 ...…………………………….......... B.S. University of the West Indies. ………………………………………………… Kingston Jamaica 1990 - 1991 …………………………………… Research Associate, Caribbean …………………. Agricultural Research and Development …………………………………………………..Institute (CARDI). Kingston Jamaica 1991 - 1994 ……………………………………. M.S. University of Florida. Gainesville, …………………………………………………..Florida 1994 - 2000 …………………………………… Scientist. Caribbean Agricultural ………………………………………………….Research and Development Institute ………………………………………………….(CARDI). Kingston Jamaica 2000 - 2004…………………………………… Graduate Teaching Assistant and …………………………………………………Research Assistant. The Ohio State …………………………………………………University FIELDS OF STUDY Major Field: Entomology Integrated Pest Management vii TABLE OF CONTENTS Page Abstract ……………………………………………………………………………… ii Dedication …………………………………………………………………………… iv Acknowledgments …………………………………………………………………… v Vita …………………………………………………………………………………... vii List of Tables ………………………………………………………………………... x List of Figures ……………………………………………………………………….. xi Glossary ……………………………………………………………………………... xv Chapters: 1. Conservation of insect natural enemies in heterogeneous vegetable landscapes 1 Introduction …………………………………………………………………. 1 Literature review ……………………………………………………………. 4 Thesis ………………………………………………………………………... 34 2 Distribution and persistence of endemic entomopathogenic nematodes In heterogeneous vegetable landscapes in Huron County, Ohio ……….………… 39 Introduction ……………………………………..…………………….….….. 39 Methodology ………………………………………………………………… 40 Results ….…………….………………….….……………………………….. 47 Discussion………………….………………….……………………………… 58 3. Life-history characteristics of endemic entomopathogenic nematode strains isolated from the vegetable production area in Huron County, Ohio ........................... 66 Introduction ......……………………………………………………….….….. 66 Methodology ………………………………………………………………… 67 Results ......…………….………………….………………………………….. 71 Discussion ..……………….………………….……………………………… 76 viii 4. Influence of host availability on the regulation of the entomopathogenic nematode, Heterorhabditis bacteriophora ............................................................... 82 Introduction…………………………………………………………….….….. 82 Methodology ………………………………………………………………… 83 Results .....….………….………………….………………………………….. 88 Discussion....……………….………………….……………………………… 91 5. Bottom-up effects of plant communities on the persistence of two strains of The entomopathogenic nematode, Heterorhabditis bacteriophora ........................ 101 Introduction ......……………………………………………………….….….. 101 Methodology ………………………………………………………………… 102 Results ......…………….………………….………………………………….. 106 Discussion ......…………….………………….……………………………… 113 6. Bottom-up factors regulating the persistence of Diadegma insulare Cresson (Hymenoptera: Ichneumonidae) in heterogeneous vegetable cropping systems ……............................................................................ 118 Introduction…………………………………………………………….….….. 118 Methodology ………………………………………………………………… 120 Results………………….………………….………………………………….. 122 Discussion………………….………………….……………………………… 123 7. Conservation biological control in vegetable systems: synthesis, possible strategies and future direction…………………………………………..…………. 135 Bibliography ………………………………………………………………………… 145 ix LIST OF TABLES Table Page 2.1 Characteristics of crop and soil sections surveyed in the vegetable production area, Celeryville (Huron County, Ohio) in 2000. …………........... 42 2.2 Soil type and disturbance regime of habitats within the vegetable landscape, Celeryville (Huron County, Ohio) in 2002 .…………... 44 2.3 Composition and abundance of arthropod populations along grassy banks adjacent to cultivated areas in Celeryville (Huron County, Ohio) in July 2001……………………………………………………………...................... 49 2.4 Multiple regression analysis of infective juvenile densities and abiotic (i.e., temperature,