Natural compounds for controlling Drosophila suzukii. A review.
The drosophilid fly Drosophila suzukii is an invasive pest that has recently started threatening fruit production in Europe. In contrast to many other fruit flies, D. suzukii is able to lay eggs in ripening and mature fruits where larvae develop, rendering fruits unmarketable. This preference for ripening fruit requires pest control shortly before harvest, implying a high risk of residues on the fruit if synthetic insecticides are used. As the current management practices largely rely on chemical control, the need for alternative solutions has emerged. Here, we review the studies published up to now on the efficacy of natural compounds against D. suzukii. Several natural compounds were identified that act as repellents, contact or ingestion toxicants, fumigants, ovicides or oviposition deterrents. The most promising compounds of each group were (i) essential oils (EOs) such as the EO of thyme or its major ingredient thymol which repelled flies from fresh fruits for at least 24 h; (ii) Leptospermum ericoides and L. scoparium EOs, which expressed contact toxicity at a LD50 <1.2 µg/fly; (iii) the combination of erythritol and sucrose, which was a potent ingestion toxicant against adults and (iv) a chitinase from Euphorbia characias against larvae (both of the latter two resulted in 100% mortality); (v) the EO ingredients perilla aldehyde, geranial and neral showed the highest insecticidal activities as fumigants (LC50 <1.52 mg/l air for males and 2.6 mg/l air for females) and (vi) powdered sulphur was reported to be the most efficient oviposition deterrent, reducing the number of eggs deposited into the fruits by 76%. To enable a wider use of the natural compounds in sustainable agriculture, more information on (i) potential effects on non-target organisms, (ii) field performance and (iii) life cycle analyses results is currently needed.