Exploitation of interspecific signals to deter oviposition by spotted-wing drosophila

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The worldwide invasive fruit pest, Drosophila suzukii, commonly known as spotted wing drosophila (SWD), has spread from Southeast Asia in recent years, causing damage to fruit crops in many countries. The fly was first detected in the UK in Southern England (2012) and its population has subsequently increased and spread north, causing loss of fruit estimated at £20-£30 million pa. All four berry crops are affected (raspberry, strawberry, blueberry and blackberry), in addition to stone fruit (especially cherries). The threat caused by SWD means that many growers are forced to apply increased numbers of applications of insecticides. This strategy is not sustainable for the long term: there are already restrictions aimed at minimizing insecticide residues in fresh produce and preventing the emergence of resistance. Spraying insecticides also compromises the management programmes that growers follow to control other pests, which often include using beneficial natural enemies to reduce pest populations to acceptable levels. In this three-year research project, we will exploit the strong natural interspecific interactions between SWD and its sister species within the Drosophila melanogaster species group to develop a novel approach to control of the pest. The project will identify new chemical oviposition deterrents that can be applied within the cropping area to deter fruit damage by SWD as a new component of IPM strategies.The existence of these interspecific oviposition deterrents and their effects on SWD have been demonstrated in our recent experiments. Egg-laying (oviposition behaviour) by SWD was very strongly inhibited following previous exposure of the substrate (fruit or artificial media) to egg-laying by D. melanogaster. Even low numbers of D. melanogaster (five mated females) had strong and persistent inhibitory effects on SWD, with 87% fewer SWD eggs deposited on the substrate that was previously exposed to D. melanogaster, compared with unexposed substrates. This suggests that SWD detect a chemical signal released by D. melanogaster and that this chemical communication between the species results in very strong inhibition of egg laying by the pest.In this research programme, we will investigate which stage of D. melanogaster (adults or eggs) releases the chemical signals that are responsible for reducing egg-laying by SWD. We will extract the active chemicals from D. melanogaster (and other Drosophila species if these prove to be more effective) and apply the signals (without D. melanogaster individuals present) to egg-laying substrates to demonstrate that the chemical alone is responsible for deterring SWD. We will investigate how SWD detect the active chemical and show whether this is via smell (of relatively volatile chemicals) or taste (non-volatile), by investigating responses of flies that have sense organs missing (removed surgically) or not working (due to genetic modification). This will identify the sense organs responsible for the detection of the chemical deterrent (e.g. the antennae or the mouthparts). We will also record electrical responses of these sense organs to components of extracts that have been separated out (e.g. using chromatography techniques). Combined with other analytical chemistry techniques, we will identify the chemical structure of the active chemical signal for synthesis in the laboratory. Behavioural and electrophysiological effects on SWD will be tested to confirm egg laying deterrent activity, initially, in small-scale lab studies and then in the field on raspberry and strawberry crops. In consultation with growers and representatives from industry, we will design new approaches to pest management that include deploying oviposition deterrents. This research programme will therefore lead to the discovery of new scientifically valuable information on insect signalling and the implementation of new approaches to crop protection.