Lure design for Drosophila suzukii based on liquid culture of fruit epiphytic yeasts: Comparing the attractivity of fermentation volatiles for seasonal morphs

The spotted-wing vinegar fly (Drosophila suzukii) is currently one of the most serious, invasive pest of berry crops worldwide. Most drosophilids are known to be attracted to fermentation volatiles produced by fruit epiphytic yeasts. Therefore, vinegar and wine baits are widely used in field trapping. However, these traps are not selective for spotted-wing drosophila. We wished to exploit the previously discovered tight-knit relationship between this vinegar fly and a fruit-colonizing yeast, Hanseniaspora uvarum, and utilize this in the design of a selective lure. Field trapping experiments were carried out in a commercial cherry orchard to evaluate the attractiveness of bottle traps baited with liquid culture of four epiphytic yeast species on stone fruits and soft-skinned fruits: H. uvarum, Metschnikowia pulcherrima, Pichia terricola and Saccharomyces cerevisiae as well as the mixed culture of the first two species. We also completed experiments using apple juice inoculated with H. uvarum. We compared the attractivity of yeast culture baits for D. suzukii and other drosophilids with that of apple cider vinegar. To explore the relationship between lure volatile emission and trap efficiency, solid-phase microextraction (SPME) was used to measure the headspace of the freshly prepared and 3-day-old lures collected from the field. Headspace samples were analysed for their volatilome with gas chromatography coupled mass spectroscopy. The H. uvarum-containing lures were more specific for D. suzukii than other yeast tested, and the attractivity was significantly higher if it was inoculated in apple juice. H. uvarum-fermented apple juice lures were more specific for female D. suzukii than the traditional apple cider vinegar lures. Winter-morph females showed an altered preference for yeast volatiles in the absence of fruit substrate.