ATTRACTIVENESS OF ENGLISH THYME (THYMUS VULGARIS L.) TO ARTHROPOD NATURAL ENEMIES AND ITS SUITABILLITY AS A DUAL USE RESOURCE A Thesis presented to the Faculty of California Polytechnic State University, San Luis Obispo In Partial Fulfillment of the Requirements for the Degree Master of Science in Agriculture with a specialization in Plant Protection Science by Kristina K Van Wert June 2020 © 2020 Kristina K Van Wert ALL RIGHTS RESERVED ii COMMITTEE MEMBERSHIP TITLE: Attractiveness of English Thyme (Thymus vulgaris L.) to Arthropod Natural Enemies and Its Suitability as a Dual Use Resource AUTHOR: Kristina K Van Wert DATE SUBMITTED: June 2020 COMMITTEE CHAIR: Dr. David H. Headrick, Ph.D. Professor of Horticulture and Crop Science COMMITTEE MEMBER: Dr. Benjamin Hoover, Ph.D. Associate Professor of Horticulture and Crop Science COMMITTEE MEMBER: Maria Elena Murrietta Farm Advisor Assistant at San Luis Obispo County Cooperative Extension iii ABSTRACT Attractiveness of English Thyme (Thymus vulgaris L.) to Arthropod Natural Enemies and Its Suitability as a Dual Use Resource Kristina K Van Wert Current agroecosystem management practices have a negative effect on natural enemies and their ability to control insect pests. Conservation biological control through the addition of flowering resources can manage food resources for natural enemies. These floral resources can also provide multiple ecosystem services. Study goals were to determine if perennial Thymus vulgaris L. was attractive to natural enemies and if so, could it be a dual use resource encouraging pest management and providing harvestable product. In 2018 plots in three locations were used to examine the effect of habitat throughout the growing season on the attractiveness of T. vulgaris. Large numbers of Thysanoptera and Hemiptera were collected in all locations, represented by phytophagous Aphididae and Thripidae, and predatory Anthocoridae. Location influenced other families to varying degrees. Seasonal specimen counts were influenced by vegetation density, floral phenology, and predator/prey relationships. In 2019 replicated plots of three treatments were used to examine if harvesting plant material affected the attractiveness of T. vulgaris to natural enemies. Total specimens in 2019 were not significantly different among treatments, indicating removal of blooms did not significantly affect the attractiveness of T. vulgaris. Significant numbers of Thysanoptera and Hemiptera were again collected in all treatments, represented by phytophagous Aphididae and Thripidae. Greater numbers of Diptera and Hymenoptera were also collected. Significant numbers of Thripidae, Aphididae, Mymaridae, and Platygastridae were found in the Family level analyses. Results from both years indicate T. vulgaris was attractive to natural enemy and phytophagous Families. Data from 2018 suggest natural enemy families were attracted to alternative prey and hosts utilizing the foliage rather than flowers but the use of nectar and pollen cannot be ruled out. Data from 2019 suggest the presence of flowers played an important role in the attractiveness of T. vulgaris to micro-hymenopteran parasitoids, Syrphidae, and native Apidae. In conclusion, Thymus vulgaris has the potential to be a dual use floral resource that benefits growers through supporting native enemy populations and pollination services, as well as provide income from the harvest of foliage. It could also be used as a beneficial, harvestable floral resource in urban gardens to encourage pollinator conservation and natural pest control. Keywords: Thymus vulgaris, Natural Enemy, Conservation Biological Control, Floral Resource, Alternative Prey, Dual Use, Ecosystem Service, Regulating, Provisioning. iv ACKNOWLEDGMENTS I would like to thank my graduate committee, in particular Dr. Headrick, for their inspiration, guidance, and patience, as well as the Cal Poly College of Agriculture, Food & Environmental Sciences and the Horticulture and Crop Science Department for their generous financial support. I would also like to thank my co-workers at Cal Poly Architecture Department and Landscape Services for their flexibility and support of my educational goals. Finally, I want to express my love and gratitude to my parents Lance and Charlotte for their continual support through the roller coaster years of my life, and to my partner Tyson for his encouragement, assistance, and understanding as this project took over our lives for several years. I couldn’t have done this without you. v TABLE OF CONTENTS Page LIST OF TABLES ................................................................................................. ix LIST OF FIGURES .............................................................................................. xv CHAPTER 1 INTRODUCTION ............................................................................................... 1 2 LITERATURE REVIEW ..................................................................................... 5 2.1 Biological Control ....................................................................................... 5 2.1.1 Classical Biological Control ................................................................... 6 2.1.2 Augmentative Biological Control .......................................................... 7 2.1.3 Conservation Biological Control ........................................................... 8 2.2 Floral Resources ........................................................................................ 8 2.2.1 Shelter and Overwintering ................................................................... 9 2.2.2 Alternative Prey or Hosts ................................................................... 10 2.2.3 Nectar and Pollen ............................................................................... 11 2.3 Selection of Floral Resources .................................................................. 12 2.3.1 Flower Attractiveness ......................................................................... 13 2.3.2 Flower Accessibility ............................................................................ 15 2.3.3 Nectar and Pollen Quality and Quantity ............................................ 17 2.3.4 Floral Resources Selectivity............................................................... 19 2.4 Floral Resources for the Provision of Ecosystem Services .................... 20 2.5 English Thyme, Thymus vulgaris L.......................................................... 23 3 MATERIALS AND METHODS ........................................................................ 27 3.1 Overview ................................................................................................... 27 3.2 2018 Attraction Study ............................................................................... 28 vi 3.2.1 2018 Study Locations ......................................................................... 28 3.2.2 2018 Plant Material ............................................................................ 28 3.2.3 2018 Study Design ............................................................................. 29 3.2.4 2018 Data Collection .......................................................................... 31 3.2.5 2018 Specimen Identification ............................................................. 32 3.3 2019 Dual Use Study ............................................................................... 33 3.3.1 2019 Study Location .......................................................................... 33 3.3.2 2019 Plant material ............................................................................ 35 3.3.3 2019 Study Design ............................................................................. 35 3.3.4 2019 Treatments ................................................................................ 37 3.3.5 2019 Data Collection .......................................................................... 38 3.3.6 2019 Specimen Identification ............................................................. 42 3.4 Data Analysis ........................................................................................... 43 4 RESULTS ........................................................................................................ 46 4.1 2018 Collection Location Analyses.......................................................... 46 4.2 2018 Collection Date Analyses ................................................................ 50 4.3 2018 Order Level Analyses ..................................................................... 55 4.4 2018 Family Level Analyses .................................................................... 60 4.4.1 2018 Overall Family Categorized by Specimen Sums...................... 60 4.4.2 2018 Top Agriculturally Important Families Analyses ....................... 66 4.4.3 2018 Top Agriculturally Important Families Collection Date Analyses .............................................................................................. 71 4.5 2018 Feeding Styles Analyses ................................................................ 80 4.6 2019 Treatment and Plot Analyses ......................................................... 86 4.7 2019 Order Level Analyses ..................................................................... 92 4.8 2019 Family Level Analyses .................................................................... 97 vii 4.8.1 2019 Overall Family Categorized by Specimen Sums.....................