In search of a better fly trap: chemical and visual ecology of Drosophila suzukii

Little, Catherine M. (2020) In search of a better fly trap: chemical and visual ecology of Drosophila suzukii. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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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 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.

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