An efficient lure and trap for the control of Drosophila suzukii

The fruit fly Drosophila suzukii, native to Asia, invaded Europe and North America almost simultaneously around 2008. This small fly species, of which the males have conspicuous black spots on the wings, rapidly spread across these continents and became a key pest of soft-skinned fruits like berries, cherries and grapes. In contrast to almost all Drosophila species, D. suzukii females have a serrated ovipositor that allows them to pierce the skin of healthy, maturing fruits and lay their eggs in the fruit flesh. This species thus is evolutionary adapted to use healthy ripening fruits for its oviposition and shows a corresponding strong preference it, hence reducing competition with other Drosophila species that are only able to use overripe, damaged or rotten fruits for egg laying. Due to its wide range of crop and non-crop hosts and its short reproductive cycle, D. suzukii is hard to manage and a thus a serious economic pest. D. suzukii’s eggs hatch in the fruit and the larval development inside the fruit renders it unmarketable. As there is a zero-tolerance for D. suzukii damage in the marketing of fruits, in many cases growers are forced to return to calendar-based sprays of the few effective (broad spectrum) insecticides. The past decade, worldwide research efforts have aimed to develop alternative control measures. This work focused on the use of traps for the management of D. suzukii, traps can be used either for monitoring or for direct control by reducing the pest population (i.e. mass trapping). For mass trapping, ideally traps require no servicing after deployment. This means that traps should be furnished with both a non-saturating and persistent killing mechanism and an olfactory attractant that has a controlled release as long as control is needed. By comparing traps with and without tunnel entries and/or killing agents we have shown the high importance of fly retention in D. suzukii traps. Tunnel entries and a pyrethroid insecticide on the inside of the transparent lid of the trap could strongly increase trap catches. Worldwide monitoring studies reported a unexpectedly low trap captures with the standard fermentation baits like apple cider vinegar (ACV) during summer, in this work it was shown that this is the result of low attractivity and not population dynamics. We have demonstrated that during summer D. suzukii flies are more attracted to fruit odours and that their preference between fermentation (ACV) and fruits odours is affected by their physiology. Protein deprived females, males and virgin females had a clear olfactory preference for ACV (food cue), while mated females provided with a complete diet preferred fruit odours (oviposition cue). When investigating the potential of mass trapping, we considered this context-dependency of olfactory attractivity and tested both under spring as summer conditions. The first estimates of trap attraction radii and consequently the required trap densities for mass trapping D. suzukii were acquired with a method based on the quantification of interference between traps in a grid. After the first year in this study, it was concluded that the tested synthetic lure needed to be further optimised. Once the lure was significantly improved, the exact experiment was repeated with addition of that improved lure. Synthetic lures were found to perform equally or better than the reference fermentation bait (ACV) from June onwards and workable estimated trap densities were achieved for the highly applicable dry traps containing controlled-release lure dispensers and a killing agent. In this thesis a method to safely and effectively mark D. suzukii flies with fluorescent pigment powders was developed. A simple application method was found to provide a persistent and easy detectable mark, without indications of affecting the survival and behaviour of the flies. This method can be used to further investigate the olfactory preferences, trap attractivity, dispersal and population dynamics of D. suzukii. Our findings can serve as a base for the further development of mass trapping strategies of D. suzukii.