INFORMATION TO USERS This manuscript has been reproduced from the microfihn master. UMI films the t%t directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9” black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell & Howell Information Company 300 North Zed) Road, Ann Arbor MI 48106-1346 USA 313/761-4700 800/521-0600 EFFECTS OF VEGETATIONAL DIVERSITY ON THE POTATO LEAFHOPPER DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Timothy Joseph Miklasiewicz, M. Sc. The Ohio State University 1997 Dissertation Committee: Professor Ronald B. Hammond, Adviser Approved by Professor David J. Hom Professor Benjamin L Stinner Professor Daniel L. Jeffers Adviser Department of Entomology UMI Number: 9801747 UMI Microform 9801747 Copyright 1997, by UMI Company. Ail rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 Copyright by Timothy J. Miklasiewicz 1997 It is better to travel well than to arrive. -Old Tibetan saying ABSTRACT The effects of differences in vegetational diversity upon abundance and behavior of the potato leafhopper, Empoasca fabae (Harris) (Homoptera: Cicadellidae), were examined in four agroecosystems. Each cropping system employed the same planting density and dispersion of a potato leafhopper host plant, soybean {Glycine max (L) Merr.). One of the four cropping systems was a soybean monoculture; the other 3 cropping systems were relay intercropping systems that varied in the number of wheat rows planted between soybean rows. Wheat {Triticum aestivum L. ) is known to be a non-host plant for the potato leafhopper. Together, the four cropping systems form a gradient of vegetational diversity, that is, of host/non-host concentration. Because of the nature of the relay intercropping systems, a distinction is made between the early part of the season, during which soybean and wheat are co-present in experimental plots, and the period following the wheat harvest, when all four cropping system s are soybean monocultures. Two experiments were conducted to test whether the leafhopper showed an inverse response to increasing amounts of the non-host., as predicted by the resource concentration hypothesis. In the first experiment, estimates were made of potato leafhopper absolute density on soybean using a portable suction device. Prior to the wheat harvest, potato leafhoppers were substantially and significantly more abundant in the soybean monoculture than in any of the intercropping systems. Mean densities were extremely low in all the intercropping systems. After the wheat harvest, the disparities between the soybean monoculture and intercropping systems gradually decreased, and fewer collection dates showed significant differences. However, potato leafhopper densities remained greater In the soybean monoculture than In the other systems until late In the season. Females and males showed similar population trends and differences among cropping systems. There were no significant differences In density detected among the intercropping systems. The second study measured colonization of the four cropping systems using water pan traps located within the soybean canopy and wheat canopy. The presence of wheat In the intercropping systems strongly Inhibited potato leafhopper from making contact with the soybean canopy until after the wheat harvest The great majority of sampling Intervals tested had significantly more potato leafhoppers detected within the soybean canopy In the soybean monoculture than In the Intercropping systems. Within the Intercropping systems, relatively high numbers of leafhoppers trapped within the wheat canopies showed that migrating potato leafhoppers contacted the wheat, but few were trapped within the corresponding soybean canopies of the same cropping systems. There were essentially no differences In colonization among the Intercropping systems. Following the wheat harvest, the disparity In soybean canopy colonization diminished rapidly. The results Indicate that colonization of soybean. Inhibited by the presence of wheat. Is an Important mechanism In producing the substantial differences In density observed among the cropping systems. Potato leafhopper exhibited a qualitative type of response to the presence of the non-host, rather than quantitative. This was Indicated by the lack of differences In density or colonization among the three Intercropping systems, despite large differences In the amount of wheat present, and differences In host quality. Ill DEDICATION This dissertation is dedicated to my family, especially to my wife, parents, brother and sister’s family, and to my friends, in appreciation of their love and support. IV ACKNOWLEDGEMENTS I owe a serious and sincere debt to my adviser, Ron Hammond, for his untiring and selfless efforts, ideas, support, and encouragement in seeing this dissertation through to this phase. I don't believe there's really any way I can thank him enough. Secondarily, I'd like to thank Dave Hom for his help and inspiration through the years; for bringing me to OSU, teaching and entertaining me in class, finding niches to fit me into, serving as Co-Adviser to this project (I should have consulted you much more), and for smoothing the way through many difficult interfaces. Thanks to Dan Jeffers for teaching me so much about crop ecology, agronomic procedures, and equipment; and for his great sense of humor and perspective. I'd like to thank Ben Stinner for serving on my Guidance Committee, for his advice and loaning me equipment and space to work. I express my gratitude to all of the above for their help with this document and for their forbearance of multiple last-minute submissions. I'd also like to thank the families of all of the above, for many favors, calls at unusual hours, and unorthodox requests. Thanks to members of the soybean lab for so much hard work, especially Judy Smith and Elaine Ressler for their great organizational skills, expertise, and labor. Kaitlin Lucas, Gwen Ruprecht, Jeremy Wienwille, Laura Richmond, Wendy Riggenbach, and others provided help with collecting and processing samples. Others among the technical staff at OARDC that were especially helpful were Kevin Power, Mark Belcher, Mike Dunlap, Dave McCartney, Dan Fickle, Jim Mason, Bill Styer, Roger Downer, Terry Moore, and Millie Casey. Others at miscellaneous satellites of the Entomology Department who need to be thanked are the entire Extension Entomology staff, especially Celeste Welty, Dave Shetlar, Hal Wilson, Julie Steele, Jeannette Jansen, Jean Steva, and Lynn Berry. John Flessel helped with references, advice, good stories, assistance with meetings, pig roasts, and loan of equipment Thanks to Rich Hall for his good advice and the opportunity to TA with him. Roger Williams provided equipment, literature, and many interesting and enjoyable discussions. Bob Treece facilitated my presence at Wooster by providing funds for an associateship. Dick Lindquist and Skip Nault helped with continued support, good humor, and sound answers to many many forwarded questions from among the public-at-large. Thanks to Roy Rings and George Shambaugh for many good discussions, help with reference material and for providing some historical perspective. Mabel Kirchner and Max Johnson helped me in innumerable ways with administrative requirements and with locating things and people through the years. When Mabel told me recently that there were things about the Department that she didn't know, I knew it was time to move on! Betty, Linda, and Rena in the Columbus Departmental Office always found a way to accomplish what I needed to have done. Chuck Triplehorn, Norm Johnson, and Andrey Sharkov provided access to the Museum of Biodiversity Collections and help with leafhopper systematics. Derrick Blocker was of great help in confirming and correcting identification of leafhoppers; Andy Hamilton provided taxonomic advice and references. John Huber and Serguei Triapitsyn identified mymarids and discussed parasite ecology and host relationships. Brian Sugarman and Paul McMillen in the Crop & Soil Science Department, Charlie Mabry of Entomology, and Bill Bardoll of Plant Pathology were invaluable in assisting with planting and harvesting experimental plots. The expertise