Searching for a biological control agent in Asia
Parasitoid laying eggs in Drosophila larvae
Partners in DROPSA are investigating parasitism of Drosophila suzukii in the region of origin of the fly. Several parasitoids have been collected in China and Japan, and significant parasitism rates have been observed. Parasitoids are now reared in quarantine and if some of them appear specific to D. suzukii, they may well represent the most promising solution for a long-term control of D. suzukii in Europe.
Classical Biological Control
Drosophila suzukii is particularly difficult to control because of its short generation time and its very broad host range, including many wild and ornamental plants. The occurrence of D. suzukii during most of the year in a wide variety of habitats requires the development of an area wide management approach. Insecticides, mass trapping and sanitation measures are locally efficient but cannot be used on a large scale in non-crop habitats. Classical biological control through the introduction of specific parasitoids from the region of origin of the fly may represent the only long term solution for a sustainable area wide control of the fly.
Surveys in Asia
Biological control specialists at CABI and INRA, with the collaboration of the Yunnan Agricultural University in China and the University of Hokkaido in Japan, are presently investigating the natural enemy complex of D. suzukii in East Asia. In 2015, fruits were collected in various regions to rear out parasitoids. Parasitism was highly variable between regions but, in Yunnan (Southern China), where D. suzukii populations are lower than in Europe and Northern China, parasitism rates higher than 50% were observed, suggesting that parasitism probably plays an important role in the natural control of D. suzukii in its region of origin. Further surveys in Asia are planned for 2016.
Study of the parasitoids
Several hymenopteran parasitoid species of the families Figitidae, Braconidae and Pteromalidae were collected in Asia. They are presently being studied in Europe and Asia by DROPSA partners to assess their suitability for biological control. In particular, they are being tested against a range of European and Asian Drosophila spp. to evaluate their specificity for D. suzukii, and assess potential non-target effects. Their preference for specific micro-habitats (fresh fruits, rotten material, etc.) is also assessed. First results are promising and show that some parasitoid species may be specific to D. suzukii feeding in fresh fruits. It must be noted that DROPSA will provide recommendations for classical biological control to the EU and Member States, but no release of exotic parasitoids in Europe will be carried out in the framework of the project.
CABI (Switzerland/United Kingdom)