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Interactions Between a Leaf-Galling Wasp and Its Invasive Hawkweed Hosts

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Interactions Between a Leaf-Galling Wasp and Its Invasive Hawkweed Hosts INTERACTIONS BETWEEN A LEAF-GALLING WASP AND ITS INVASIVE HAWKWEED HOSTS GREGORY HOLMES Bachelor of Science, University of Lethbridge, 2013 A Thesis Submitted to the School of Graduate Studies of the University of Lethbridge in Partial Fulfillment of the Requirements for the Degree MASTER OF SCIENCE Department of Biological Sciences University of Lethbridge LETHBRIDGE, ALBERTA, CANADA © Gregory Holmes, 2016 INTERACTIONS BETWEEN A LEAF-GALLING WASP AND ITS INVASIVE HAWKWEED HOST GREGORY HOLMES Date of Defence: June 20, 2016 Rosemarie De Clerck-Floate Research Scientist Ph.D. Co-supervisor Robert Laird Associate Professor Ph.D. Co-supervisor Syama Chatterton Research Scientist Ph.D. Committee Member Cameron Goater Professor Ph.D. Committee Member Theresa Burg Associate Professor Ph.D. Chair, Thesis Examination Committee I would like to dedicate this thesis to my wonderful wife, Jessica, and to my parents. Their unfailing support has allowed me to pursue my dreams in all of life's endeavors. iii Abstract This thesis aims to explore the interactions between a potential biocontrol agent, the gall-wasp Aulacidea pilosellae, and its invasive Pilosella hawkweed hosts. I discovered that increased nitrogen availability improves P. officinarum vegetative growth, while also interacting with A. pilosellae to reduce vegetative growth, as the plants cannot compensate for this herbivory. I did not detect any nitrogen effects on wasp performance. I also explored how the host species utilized for galling affects wasp performance through two generations by measuring maternal effects. These only influenced offspring performance when the mother had utilized P. caespitosa, but not P. glomerata. I discovered that P. caespitosa is also the better offspring host, producing significantly larger galls and heavier larvae compared to P. glomerata. These results may help identify, 1) if underlying site fertility may be associated with increases in agent performance and/or impact on the target weed, and 2) to indicate the appropriate Pilosella species to target in a biocontrol programme. iv Acknowledgements This project would not have been possible without the support of many people, in- and out-side of the lab. I would like to thank my two supervisors, Rose De Clerck-Floate and Robert Laird, who read my numerous revisions and guided my along my path. They have given me support, encouragement, and enthusiasm for my project and various ideas which may or may not have come to fruition. I would like to thank my committee members, Syama Chatterton and Cam Goater, who have also helped keep me on track when I wanted to bite off more than I could chew. Thank you to Eva Pavlik, for your passion for insects, and for teaching me how to care for insects and stay organized when things don't go as expected. I continue to learn from you and your ways, and hope to maintain my enthusiasm as you have. Thank you to the several students who have helped me with all of my data collection, data entry, regular maintenance of wasp colonies and for helping keep our lab a clean and safe environment (Candace Griffith, Leah Brummelhuis, Jayden Dyck, Curtis Farrus). Your aid has allowed me to stay sane and energetic during long hours and unforeseeable setbacks. Thanks go to the many other graduate students whom I have shared my journey with. I always enjoy learning about other projects, and speaking to those who are as passionate about their research as I am about mine. Having the option to bounce ideas back and forth with you has allowed many insights into my own project, and I hope our discussions have helped you as much as they have helped me. v This research was supported by the B.C. Ministry of Forests, Lands and Natural Resource Operations, Agriculture and Agri-Food Canada, and the Alberta Conservation Association. vi Table of Contents Abstract ............................................................................................................................................ iv Acknowledgements........................................................................................................................... v Table of Contents ............................................................................................................................ vii List of Tables .................................................................................................................................... ix List of Figures .................................................................................................................................... x Chapter 1: Introduction ....................................................................................................................1 Thesis Goals ...............................................................................................................................1 Nitrogen effects on biodiversity and invasive weed species .....................................................2 Nitrogen effects on herbivore preference, performance, and impact ......................................5 Environmental heterogeneity and maternal effects .............................................................. 12 Gall-forming insects ............................................................................................................... 15 Biological control of Pilosella hawkweed species .................................................................. 19 Experimental objectives ......................................................................................................... 23 Chapter 2: Interactive effects of a leaf-galling wasp and nitrogen on an invasive hawkweed species ............................................................................................................................................ 26 Introduction ............................................................................................................................... 26 Materials and Methods .............................................................................................................. 32 Plants ..................................................................................................................................... 32 Insects .................................................................................................................................... 33 Experimental design ............................................................................................................... 34 Non-destructive plant performance measurements .............................................................. 35 Destructive plant performance measurements ..................................................................... 35 Wasp performance measurements ........................................................................................ 36 Nitrogen analysis ................................................................................................................... 36 Statistical analysis .................................................................................................................. 37 Results ........................................................................................................................................ 37 Dry weights and leaf senescence ........................................................................................... 37 Vegetative and reproductive growth ..................................................................................... 38 Leaf nitrogen content ............................................................................................................. 39 Aulacidea pilosellae performance .......................................................................................... 40 vii Discussion .................................................................................................................................. 47 Chapter 3: Maternal and offspring host effects on the performance of a leaf-galling wasp ........ 55 Introduction ............................................................................................................................... 55 Materials and Methods .............................................................................................................. 58 Plants ..................................................................................................................................... 58 Measurements ....................................................................................................................... 62 Statistical analysis .................................................................................................................. 63 Results ........................................................................................................................................ 64 Maternal Trial......................................................................................................................... 64 Offspring Trial ........................................................................................................................ 64 Discussion .................................................................................................................................. 71 Chapter 4: Discussion ..................................................................................................................... 77 Nitrogen effects on P. officinarum performance ..................................................................
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