In search of a better fly trap: Chemical and visual ecology of Drosophila suzukii © Catherine M. Little A thesis submitted to the School of Graduate Studies in partial fulfillment of the requirements for the degree of Doctor of Philosophy Department of Biology / Faculty of Science Memorial University of Newfoundland Submitted December 2020 St. John’s, Newfoundland and Labrador Abstract Drosophila suzukii is an invasive species of concern to fruit growers throughout temperate regions worldwide. Unlike most Drosophila species, D. suzukii has an enlarged and heavily sclerotized ovipositor that allows female flies to lay eggs in fruits before they are fully ripened and, in most cases, before fruits are harvestable. Initial efforts at mitigating damage have relied on chemical pesticides to reduce D. suzukii populations in crop areas; however, on-going research efforts have focused on more environmentally sustainable integrated pest management alternatives. This thesis investigates aspects of D. suzukii behaviour and physiology that promoted its successful global invasion. Chapter one discusses the role of behavioural and physiological plasticity in giving D. suzukii an ecological edge during introduction and successful invasion. Chapter two investigates D. suzukii host selection behaviour and preference among commercial fruits and novel native fruits in a boreal environment. I investigated the fruit characters thought to play a role in host choice, including fruit sweetness (brix), fruit acidity (pH), and fruit firmness (penetration force [gfmm2]). Based on D. suzukii behaviour observed in field settings, the investigation was expanded to include the role of fruit and foliage colour in host selection. Additionally, we beta-tested a citizen science initiative to identify native fruit species at risk and to confirm the range limits of D. suzukii in Atlantic Canada. Chapter three further explores colour preference and use of colour by D. suzukii as attraction cues, first as cues to differentiate among fruits of different ripeness stages, and second as visual targets for potential use in monitoring traps. Chapter four investigates D. suzukii physiological sensitivity and behavioural activity to odorants associated with fruits and foliage, and odorants known to be important to ii other Drosophila species. An iterative process of laboratory and field trials was used to test individual odorant compounds and odorant blends in combination with results of colour preference testing to improve trapping efficacy. Given the behavioural and physiological plasticity of D. suzukii, trials were conducted among different fruit crops and growing environments. Chapter five synthesizes lessons learned about D. suzukii behaviour and preferences to make recommendations for effective monitoring traps for blueberry and raspberry crop systems. iii Acknowledgements I respectfully acknowledge that this research was conducted on the ancestral homelands of the Mi’kmaq and Beothuk peoples. I would like to thank my supervisory committee: Kirk Hillier, Tom Chapman, Deb Moreau, Peggy Dixon, and Brian Stavely for their ongoing guidance and support. I would like to thank my lab mates at Acadia University and Memorial University, including Lara Thomas, Rebecca Rizzato, Logan Gray, Heather Crozier, Simon Pawlowski, Emma Rand, Rylee Isett, Megan MacIsaac, Lise Charbonneau, Colin MacKay, Michael Light, Joel Goodwin, Jesse Saroli, Adam Discher, Ersa Gjelaj, Kate Carson, Chris Hammill, Todd Power, Andrew Chaulk, and Holly Caravan. I would also like to thank Brent Robichaud, Marlene Snyder, Dawn Miner, Tanya Morse-Outhouse, Michael Robertson, Justin Renkema, David Kristie, Melanie Prieztniz, Meghan Swanburg, Ian Fleming, Carolyn Parsons, Madonna Bishop, Shelley Vaughan, Nathan Patstone, Katrin Sommerfeld, and Susan Carbyn. This research would not have been possible without the generous support of Nova Agri Inc. (Blueberry Acres and Vital Berry Farm), MacBerry Farm, Lester’s Farm, Rodrigues Winery, Wright's Family Farm, Campbellton Family Farm, and Mark’s Market. A special thanks goes to my family and friends for their love and support. iv Table of Contents Abstract………………………………………………………………………………… ii Acknowledgements…………………………………………………………………..... iv List of tables…………………………………………………………………………… ix List of figures………………………………………………………………………….. xiii Chapter 1 General introduction…………………………………………………….. 1 1.1 Introduction……………………………………………………………………. 1 1.2 Thesis outline…………………………………………………………………... 2 1.3 References……………………………………………………………………… 4 1.4 Co-authorship statement……………………………………………………….. 7 1.5 Plasticity is key to success of Drosophila suzukii (Diptera: Drosophilidae) invasion…………………………………………………………………………. 9 1.5.1 Abstract………………………………………………………………… 9 1.5.2 Introduction…………………………………………………………….. 9 1.5.3 Phenotypic plasticity…………………………………………………… 11 Morphological plasticity………………………………………………….. 11 1.5.4 Developmental plasticity………………………………………………. 13 Temperature and desiccation tolerance…………………………………… 13 1.5.5 Behavioural plasticity………………………………………………….. 17 Plasticity in circadian activity…………………………………………….. 17 Olfactory plasticity………………………………………………………... 18 Dietary plasticity………………………………………………………….. 19 Plasticity in community interactions……………………………………… 22 1.5.6 Discussion……………………………………………………………… 24 1.5.7 Acknowledgements…………………………………………………….. 25 1.5.8 References……………………………………………………………… 25 1.5.9 Supplementary information……………………………………………. 44 Supplementary references………………………………………………… 63 Chapter 2 Host preference and suitability………………………………………….. 71 2.1 Susceptibility of selected boreal fruits and berries to the invasive pest Drosophila suzukii……………………………………………………………… 71 2.1.1 Abstract………………………………………………………………… 71 2.1.2 Introduction…………………………………………………………….. 72 2.1.3 Materials and Methods…………………………………………………. 73 Source materials…………………………………………………………... 73 Host selection – 2-choice assays………………………………………….. 74 Fruit characters……………………………………………………………. 75 Oviposition and larval success – No-choice assays………………………. 75 Statistical analysis………………………………………………………… 76 2.1.4 Results………………………………………………………………….. 76 Host selection……………………………………………………………... 76 Fruit characters……………………………………………………………. 79 Oviposition and larval success……………………………………………. 81 2.1.5 Discussion……………………………………………………………… 84 Novel host information…………………………………………………… 84 v Host preference…………………………………………………………… 86 Larval development……………………………………………………….. 87 Applications for fruit growers…………………………………………….. 87 2.1.6 Acknowledgements…………………………………………………….. 88 2.1.7 References……………………………………………………………… 89 2.1.8 Supplementary information……………………………………………. 95 2.2 Role of fruit characters and colour on host selection of boreal fruits and berries by Drosophila suzukii………………………………………………….. 97 2.2.1 Abstract………………………………………………………………… 97 2.2.2 Introduction…………………………………………………………….. 97 Key message……………………………………………………………… 101 2.2.3 Materials and methods…………………………………………………. 102 Fruit and insect sources…………………………………………………… 102 Fruit characters……………………………………………………………. 103 Fruit preference…………………………………………………………… 104 Fruit suitability……………………………………………………………. 104 Statistical analysis………………………………………………………… 105 2.2.4 Results………………………………………………………………….. 105 Fruit characters……………………………………………………………. 105 Fruit preference…………………………………………………………… 108 Fruit suitability……………………………………………………………. 108 2.2.5 Discussion……………………………………………………………… 114 2.2.6 Acknowledgements…………………………………………………….. 118 2.2.7 References……………………………………………………………… 118 2.2.8 Supplementary information……………………………………………. 129 2.3 FlySpotter: using citizen science to identify range expansion and fruit at risk from Drosophila suzukii in Nova Scotia and Newfoundland and Labrador………………………………………………………………………... 130 2.3.1 Abstract………………………………………………………………… 130 2.3.2 Introduction…………………………………………………………….. 130 2.3.3 Materials and methods…………………………………………………. 136 2.3.4 Results………………………………………………………………….. 138 2.3.5 Discussion……………………………………………………………… 148 2.3.6 Acknowledgements…………………………………………………….. 152 2.3.7 References……………………………………………………………… 152 Chapter 3 Role of colour and visual cues…………………………………………… 165 3.1 Effect of colour and contrast of highbush blueberries to host-finding behavior by Drosophila suzukii………………………………………………... 165 3.1.1 Abstract………………………………………………………………… 165 3.1.2 Introduction…………………………………………………………….. 166 3.1.3 Materials and methods…………………………………………………. 168 Fruit assays – odor not isolated…………………………………………… 170 No odor assays……………………………………………………………. 171 Statistical analysis………………………………………………………… 173 3.1.4 Results………………………………………………………………….. 174 Fruit assays – odor not isolated…………………………………………… 174 vi No odor assays……………………………………………………………. 182 3.1.5 Discussion……………………………………………………………… 188 3.1.6 Acknowledgements…………………………………………………….. 193 3.1.7 References……………………………………………………………… 193 3.1.8 Supplementary information……………………………………………. 200 3.2 Colour preference of spotted wing Drosophila, Drosophila suzukii……….. 203 3.2.1 Abstract………………………………………………………………… 203 3.2.2 Introduction…………………………………………………………….. 203 3.2.3 Materials and methods…………………………………………………. 206 D. suzukii colony………………………………………………………….. 206 Sensitivity to colour (Electroretinography)……..………………………… 206 Preference among LED light colours…………………………..…………. 208 Preference among solid colours…………………………………………... 209 Preference among contrast disks………………………………………….. 210 Statistical analysis………………………………………………………… 212 3.2.4 Results………………………………………………………………….. 212 Sensitivity to colour (Electroretinography)……………………..………… 213 Preference among LED light