Local Management and Landscape Effects on the Predator Guild in Vegetable Crops, with a Focus on Long-legged Flies (Diptera: Dolichopodidae) THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Andrea Renee Kautz, B.S. Graduate Program in Entomology The Ohio State University 2015 Master's Examination Committee: Mary M. Gardiner, Advisor Norman F. Johnson Celeste Welty Copyright by Andrea R. Kautz 2015 Abstract Biological control is a vital ecosystem service provided by a diverse guild of predators in agroecosystems. Biodiversity is thought to be linked to ecosystem functioning through more efficient resource capture via niche partitioning. Understanding the factors that impact the diversity of predators in agroecosystems is therefore important to our understanding of how to enhance biological control services. Long-legged flies (Diptera: Dolichopodidae) are a particularly ubiquitous yet understudied group of insect predators that are common in all habitats in Ohio, including agricultural systems. Previous studies have shown that these flies are sensitive to environmental changes, at least in natural systems like grasslands and reed marshes. The goal of this study was to determine how local management and landscape-scale factors such as composition and heterogeneity influence the community assemblage of Dolichopodidae, and the predator community as a whole, found in agroecosystems. During the summer of 2013 and 2014, pan trapping was used to sample the long-legged fly community present in produce farms across northeast Ohio that represented a gradient of landscape complexity and management intensity. Communities found within sweet corn, summer squash, and unmanaged old fields were surveyed. Over 3,000 flies representing eleven dolichopodid genera and 33 species were found across both years. Dolichopodid abundance was actually higher in crop habitats than unmanaged habitats, but habitat preference varied by ii genus. Landscape factors influencing the abundance of Dolichopodidae varied from year to year. Identifying which factors are driving the diversity of this family of flies will help us understand how to maximize the biological control services being provided. During the same time, above-ground and ground dwelling predators were also sampled in sweet corn and summer squash using yellow sticky cards and pitfall traps in order to quantify the predator guild as a whole. Over 26,000 predatory arthropods were counted over the two summers. Predator abundance was generally higher in squash, but community composition varied between crops. Therefore, crop diversity in a farmscape may be important for supporting a diverse predator guild. In general, more agricultural habitat in the surrounding landscape had a negative effect on the predator guild, so diversification at the landscape scale may also be an important way to promote diverse predator guilds and biological control services. iii Dedication This document is dedicated to my parents. iv Acknowledgments I would like to acknowledge my advisor Mary for her mentorship and encouragement throughout my graduate program, as well as the other members of my advisory committee, Norm and Celeste, for their guidance and wisdom. I would also like to thank Dr. Dan Bickel, Dr. Scott Brooks, and Dr. Marc Pollet for their guidance and expertise regarding Dolichopodidae, which is a very fun yet challenging group. This work would not have been possible without the help of two great lab technicians, Chelsea Gordon and Nicole Hoekstra, and all of the help provided by several undergraduate assistants and fellow members of the Gardiner Lab. v Vita June 2008 .......................................................Diploma, Perkins High School June 2012 .......................................................B.S. Zoology, The Ohio State University August 2012 to present .................................Graduate Fellow and Graduate Teaching/Research Associate, Department of Entomology, The Ohio State University Fields of Study Major Field: Entomology vi Table of Contents Abstract ............................................................................................................................... ii Dedication .......................................................................................................................... iv Acknowledgments............................................................................................................... v Vita ..................................................................................................................................... vi List of Tables ................................................................................................................... viii List of Figures .................................................................................................................... ix Chapter 1: Characterizing the Dolichopodid Community in Agroecosystems and Determining the Effect of Management and Landscape on Their Diversity and Abundance .......................................................................................................................... 1 Tables and Figures ................................................................................... 16 Chapter 2: Local Management and Landscape Effects on the Predator Guild in Vegetable Crops ................................................................................................................................. 29 Tables and Figures ...................................................................................... 43 References ......................................................................................................................... 60 vii List of Tables Chapter 1 Table 1. Sampling Schedule ............................................................................................. 18 Table 2. Dolichopodid Species Summary ......................................................................... 19 Table 3. Landscape Analysis Summary ............................................................................ 28 Chapter 2 Table 4. Sampling Schedule ............................................................................................. 45 Table 5. Predator Summary .............................................................................................. 46 Table 6. Landscape Analysis Summary 2013 ................................................................... 58 Table 7. Landscape Analysis Summary 2014 ................................................................... 59 viii List of Figures Chapter 1 Figure 1. Field Sites .......................................................................................................... 16 Figure 2. Sampling Schematic .......................................................................................... 17 Figure 3. 2013 Dolichopodidae Abundance ..................................................................... 22 Figure 4. 2014 Dolichopodidae Abundance ..................................................................... 24 Figure 5. Dolichopodidae Community Composition ........................................................ 26 Chapter 2 Figure 6. Field Sites .......................................................................................................... 43 Figure 7. Sampling Shematic ............................................................................................ 44 Figure 8. 2013 Predator Totals and Diversity ................................................................... 47 Figure 9. 2013 Pitfall Predator Abundance....................................................................... 48 Figure 10. 2013 Sticky Card Predator Abundance ........................................................... 50 Figure 11. 2014 Predator Totals and Diversity ................................................................. 52 Figure 12. 2014 Pitfall Predator Abundance..................................................................... 53 Figure 13. 2014 Sticky Card Predator Abundance ........................................................... 55 ix Chapter 1: Characterizing the dolichopodid community in agroecosystems and determining the effect of management and landscape on their diversity and abundance INTRODUCTION Sustainable agricultural practices aim to conserve biodiversity of beneficial arthropods to enhance the ecosystem services they support such as pollination and biological control (Losey and Vaughan 2006, Isaacs et al. 2012, Garibaldi et al. 2014). The biodiversity ecosystem function (BEF) hypothesis states that increasing diversity has a positive influence on ecosystem function (Cardinale et al. 2006, Duffy et al. 2007). This has been demonstrated at many trophic levels in various systems (Tilman et al. 1996, van der Heijden et al. 1998, Downing and Leibold 2002, Balvanera et al. 2006, Lundholm 2015), and generally has been attributed to greater niche partitioning leading to more efficient resource capture (Finke and Snyder 2008). If the diversity of arthropod predators supported within an agroecosystem can influence the level of biological control services provided, then a better understanding of the predator guild contributing to biological control within the system is needed. A critical first step in reaching that level of understanding is recognizing all potentially-relevant members of the predator guild present in the system, and