DISSERTATION SPIDERS AS POTENTIAL APHID PREDATORS IN EASTERN COLORADO AGROECOSYSTEMS Submitted by Lauren M. Kerzicnik Department of Bioagricultural Sciences and Pest Management In partial fulfillment of the requirements For the Degree of Doctor of Philosophy Colorado State University Fort Collins, Colorado Spring 2011 Doctoral Committee: Advisor: Frank Peairs Co-advisor: Paula E. Cushing Ruth Hufbauer Gary Peterson ABSTRACT SPIDERS AS POTENTIAL APHID PREDATORS IN EASTERN COLORADO AGROECOSYSTEMS Spiders are indigenous, ubiquitous natural enemies that have been associated with reduced pest densities and may be particularly useful in reducing aphid densities. Therefore, it is critical to determine the spider fauna within these agroecosystems, spiders that may be key biological control agents for conservation, and determine if alternative cropping systems can enhance or maintain these particular spider species. The inclusion of sustainable agricultural systems is an important component of integrated pest management. The faunal composition of spiders in eastern Colorado agroecosystems was described and analyzed to determine whether a crop-intensified system resulted in greater spider density and biodiversity than a conventional system. Three sites in eastern Colorado-Akron, Briggsdale, and Lamar-were studied. From 2002- 2007, 11,207 spiders from 17 families and 119 species were collected from pitfall, vacuum, and lookdown sampling techniques. Crop intensification had little effect on spider density or biodiversity. Spider mean densities/activity densities and biodiversity were low for all years and sites, with the exception of 2005 and 2006. At all sites, the fauna was dominated by hunting spiders in the Lycosidae and Gnaphosidae families ii (72%), which differs from the dominance of web-building spiders in western European agroecosystems. Before establishing whether predators can contribute to the biological control of a pest, it is important to determine the availability of the pest for prey. Diuraphis noxia is an important economic pest in wheat agroecosystems in Colorado. Thus, the falling rate of D. noxia from wheat infested at 1x and 10x aphid infestation levels and resistant and susceptible varieties was measured. Falling rates ranged from 0.7% to 69.5% in Fort Collins, CO, and from 1.4% to 59.5% in Akron, CO. The falling rate of D. noxia was more influenced by plant growth stage than aphid densities, with the highest falling rate occurring prior to wheat senescence. Resistant wheat plants did not have increased aphid falling rates. The falling rate of D. noxia was highest at lower aphid densities, thus epigeal predator consumption of D. noxia can occur at lower aphid densities. Nevertheless, the falling rate of D. noxia clearly indicates that these prey can represent an important food source for ground predators. It is the conservation of key species and not necessarily the conservation of predators per se that is important for effective biological control. Therefore, it is critical to identify which predators are consuming pests in the field. Species-specific primers and the polymerase chain reaction were used to determine if two dominant spiders, Tetragnatha laboriosa and Pardosa sternalis , were consuming D. noxia DNA in the field. A partial 1146 bp sequence from the mitochondrial cytochrome oxidase I (COI) gene was used and aligned with other non-target sequences to create two primer pairs that amplified a 227 bp fragment of D. noxia DNA. A total of 64 and 71 T. laboriosa and P. sternalis , iii respectively, were collected from within three D. noxia infestation levels-0x, 1x, and 10x- in Fort Collins, CO, from May-July at the following wheat stages: boot, inflorescence, anthesis, milk, and dough. Of the spiders collected in the field, 32% and 48% of T. laboriosa and P. sternalis tested positive for D. noxia DNA. Additionally, 92% of T. laboriosa were collected at the 1x or 10x D. noxia infestation levels combined, which indicated that T. laboriosa responded to increased D. noxia densities. Pardosa sternalis , however, was more evenly distributed within aphid infestation levels. iv ACKNOWLEDGEMENTS I have many people to thank for this project, and I would not have accomplished this without them. First, I would especially like to thank my two advisors, Dr. Paula E. Cushing and Dr. Frank Peairs. I am grateful for their continuous guidance and support and always having my best interests at heart. I was very lucky to have financial support throughout my time as a student through Frank and internship funding through Paula and the museum. I would also like to thank my other two committee members, Dr. Ruth Hufbauer and Dr. Gary Peterson, who were always available for questions and advice and added great comments to my dissertation. I also want to thank Dr. James Harwood (University of Kentucky). He was like an additional advisor to me and always offered his help at any time, and I will always be grateful for his help and encouragement. For the faunistic study, I have many people to thank. I would first like to thank Stan Cass and Chris Rundell, the farmers who cooperated with CSU and allowed us to conduct research projects on their fields. They are amazing individuals, and their participation in cropping systems research has been a key factor for graduate studies. For identifications, I thank Dr. Boris Kondratieff for identifying several insects and Linda Mahaffey for IDing thrips to species. For spider species IDs, I graciously thank Dr. Mike Draney from the University of Wisconsin for IDing all of my linyphiids, Dr. Fran X. Haas for v identifying all of my salticids, Joey Slowik for a variety of spider IDs, Maren Francis and Julie Whitman-Zai for agelenid IDs, Dr. Charles Dondale for the verification of Thomisid and Philodromid IDs, Dr. Robb Bennett for verifying dictynid IDs, and Dr. Herbert Levi for the verification of theridiid spiders. Additionally, I would like to thank Paula Cushing for various questions and help verifying IDs. I could not have completed my research and writing without the help and support of several amazing graduate students and staff. Terri Randolph is my hero for all of her endless support and knowledge. She reviewed drafts of all chapters of this dissertation and taught me a lot about how to present my statistics. She was an amazing help and source of guidance for me with every aspect of my research (and life!). Hayley Butler provided spiders from her Master’s research on carabid beetles at the same sites for 2002 and 2003 and helped me several times in the field. Aubrey Weiland was a great help with field and lab work for several years and in some of the worst conditions! Scott Merrill ran R on several of my diversity and density data and edited many parts of this dissertation! Other graduate students that I could not have lived without include Linda Stevens and Sherri Pucherelli. Thanks to all of you for being such amazing friends and helping me with my research! I could not have done it without you and could not imagine my life without any of you! I have worked with many fabulous undergraduates and am grateful for their help. Sam Thomason (Gray) was such an amazingly loyal worker and an asset to all of my data collection. She worked with me for several years. I will always cherish her friendship and am amazed at what a great heart she has. Betsy Bosley also worked with me for vi several summers and was also an amazing and detailed worker. Other lab assistants that I thank include Jesse Stubbs, Dan Natan, Tyler Keck, Kellin Bershinsky, Lukas Rael, Emili Talmich, Anthony Longo-Peairs, Will Pessetto, Marie Stiles, Jake Walker, Alicia Bosley, Ben Horne, and Erin Quinn. We had a lot of fun in the field, and it was great getting to know all of you. I could not have completed any of my molecular work without the graciousness of Dr. Jan Leach and Dr. James Harwood who allowed me to work in their labs. Eric Chapman and Jan Stephens also helped me immensely. In addition, several people helped me along the way, including Kayce Bell, Paula Cushing, Myron Bruce, Jacob Snelling, Marcello Zerillo, Leon Van Eck, and Tori Valdez. It was great to have so many people to talk to in the molecular world. I was a lost puppy for a while, and I appreciated all of your advice and guidance. I am so lucky to have worked with some of Frank’s amazing staff in Akron, Briggsdale, and Lamar, including Dave Poss, Thia Walker, Mike Koch, and Justin Herman. I had to coordinate with all of them to complete the faunistic study, and they were always so accommodating. They are fabulous people, and I thank them for everything they did for me. Other people I’d like to thank include Andrew Norton, who provided advice for analyzing diversity statistics for the faunisitic chapter, Dr. Robb Cramer, Dr. Matt Greenstone, Dr. Whitney Cranshaw, Matt Camper, and Jeff Rudolph. I also wanted to thank the Lloyd Cannon and Carlye Cannon Wattis Foundation and the Colorado State University Agricultural Experiment Station for funding. vii Last but not least, I am so thankful to my family, friends, and my dog, Stella, for all of their amazing support. They were always there for me throughout the process. I am forever appreciative of my husband, David, for his support and encouragement during this process. He was always by my side, and I could not have done it without him. viii TABLE OF CONTENTS ABSTRACT II ACKNOWLEDGEMENTS V LIST OF TABLES XI LIST OF FIGURES XIV CHAPTER 1- INTRODUCTION 1 LITERATURE CITED 20 CHAPTER 2-EFFECTS OF CROP INTENSIFICATION