The impact of plant identity and induced effects on within- and trans-generational disease resistance in the cabbage looper Trichoplusia ni by Kevin Colmenares-Di Maria B.Sc. Agricultural and Environmental Sciences, McGill University, 2017 Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Pest Management in the Department of Biological Sciences Faculty of Science © Kevin Colmenares-Di Maria 2021 SIMON FRASER UNIVERSITY Summer 2021 Copyright in this work is held by the author. Please ensure that any reproduction or re-use is done in accordance with the relevant national copyright legislation. Declaration of Committee Name: Kevin Colmenares-Di Maria Degree: Master of Pest Management Title: The impact of plant identity and induced effects on within- and trans- generational disease resistance in the cabbage looper Trichoplusia ni Committee: Chair: Dr. Julian Christians Professor, Biological Sciences Dr. Jenny Cory Supervisor Professor, Biological Sciences Dr. Gerhard Gries Committee Member Professor, Biological Sciences Dr. Juli Carrillo Committee Member Assistant Professor, University of British Columbia Dr. Michelle Franklin External Examiner Research Scientist, Agassiz Research and Development Center ii Abstract Secondary plant metabolites can have a significant impact on the susceptibility of Lepidoptera to baculovirus infection, both directly and indirectly, and thus can play a major role in determining insect fitness. Here I first examine the effects of diet complexity on the resistance of the cabbage looper (Trichoplusia ni) to a nucleopolyhedrovirus (TnSNPV). I then tested whether induction of plant secondary chemicals as a result of insect feeding impacts transgenerational disease resistance. I found that larvae fed on a mixed plant diet had similar resistance to virus as larvae fed on single species diets. However, larvae fed on tomato prior to virus challenge had higher resistance to virus, compared to those fed on cabbage and broccoli. Plant induction did not affect transgenerational virus resistance, although offspring mortality was lower for insects whose parents fed on broccoli compared to cabbage. This suggests that plant defensive chemistry has longer-term, indirect effects on disease resistance which could impact host dynamics. Keywords: mixed diet; nucleopolyhedrovirus; disease resistance; transgenerational effects; immunity; plant induction iii Dedication To mom, dad, Patrick and Erika iv Acknowledgement I’d like to firstly thank my senior supervisor Dr. Jenny Cory for all her guidance and wisdom on all things insect and ecology related. Thank you for the feedback on the many, many drafts and thank you for not giving up on me. My gratitude also goes to my committee members, Dr. Gerhard Gries and Dr. Juli Carrillo, for their invaluable insight and perspective on the many stages and experiments of my thesis. I’d also like to thank my Cory lab mates past and present for their friendship and support; to Paul, Joyce, Heather, Stacey, Kari, Sean and Dennis. I want to single out and give a special thanks to Pauline Deschodt for mentoring me, and without whom much of my experiments would not have been possible. Also, a big thank you to all my fellow grad student friends I’ve made over the years who are too numerous to name. A big thank you to Regine Gries for her patience and humour when an exasperated grad student asked her for guidance on the many problems involving chemistry. Thank you to my legion of volunteers that have helped me over the years; Sarah, James, Faatimah, Sophie, Brandon, Juan and more. Lastly, this research would not have been possible without funding from SFU, and the donors that contribute funds to the following scholarships; Thelma Finlayson Graduate Entrance Scholarship, Dr. John Yorston Memorial Graduate Scholarship in Pest Management and the H.R. MacCarthy Graduate Bursary. v Table of Contents Declaration of Committee .................................................................................................... ii Abstract ............................................................................................................................... iii Dedication ........................................................................................................................... iv Acknowledgement................................................................................................................v Table of Contents ................................................................................................................ vi List of Tables ..................................................................................................................... viii List of Figures...................................................................................................................... ix List of Acronyms ................................................................................................................. xi Chapter 1. General Introduction ................................................................................ 1 1.1. Study system ............................................................................................................ 5 1.1.1. Cabbage looper, Trichoplusia ni ................................................................. 5 1.1.2. Host Plants .................................................................................................. 5 1.1.3. Baculoviruses .............................................................................................. 6 1.1.4. Research questions .................................................................................... 7 1.A. References ................................................................................................................. 8 Chapter 2. The effect of mixed plant diets on Trichoplusia ni growth and resistance to a nucleopolyhedrovirus (TnSNPV).............................................. 19 Abstract ............................................................................................................................. 19 2.1. Introduction ............................................................................................................. 19 2.1.1. Cost of chemicals on the immune system and pathogen infection.......... 22 2.1.2. System and Experiment ............................................................................ 23 2.2. Materials and Methods ........................................................................................... 23 Insects and Virus .................................................................................................... 23 2.2.1. Host Plants ................................................................................................ 24 2.2.2. Diet Experiment ........................................................................................ 24 2.2.3. Virus Bioassay .......................................................................................... 25 2.2.4. Statistical Analysis .................................................................................... 25 2.3. Results .................................................................................................................... 27 2.3.1. Diet complexity and larval performance ................................................... 27 2.3.2. Viral Bioassay ........................................................................................... 34 2.4. Discussion ............................................................................................................... 35 2.4.1. The effect of plant identity and increasing diet complexity on insect fitness-related traits................................................................................... 36 2.4.2. The effect of plant identity and increasing diet complexity on disease resistance .................................................................................................. 39 2.A. References ............................................................................................................... 43 Chapter 3. The transgenerational effects of host plant and plant induction on Trichoplusia ni fitness and virus resistance ..................................................... 56 Abstract ............................................................................................................................. 56 vi 3.1. Introduction ............................................................................................................. 56 3.2. Materials and Methods ........................................................................................... 60 3.2.1. Insects ....................................................................................................... 60 3.2.2. Plants ........................................................................................................ 61 3.2.3. Experimental Design ................................................................................. 61 Parental Generation ................................................................................................ 61 Mating and egg collection ....................................................................................... 62 Virus bioassay ......................................................................................................... 62 Statistical analysis................................................................................................... 63 3.3. Results