Biological Control
Early experiments tested the efficacy of Phaenopria spp. (Hymenoptera: Diapriidae) under laboratory conditions, but results were unsatisfactory (Kanzawa, 1939).<br>Studies to determine the current presence of indigenous parasitoid biological control agents and their efficacy in controlling D. suzukii were undertaken both in North America and in Europe by different research groups (Brown et al., 2011;Chabert et al., 2012;Rossi Stacconi et al., 2013). Under laboratory conditions several naturally occurring parasitoids of drosophilids in France were able to successfully parasitize D.suzukii. These included two larval parasitoids, Leptopilina heterotoma and Leptopilina boulardi, and two pupal parasitoids, Pachycrepoideus vindemiae (Hymenoptera: Pteromalidae) and Trichopria drosophilae (Hymenoptera: Diapriidae). Both Leptopilina parasitoids displayed high parasitism rates on D. suzukii, but because of the strong immune response of the host larvae, they did not give rise to an adult wasp (Chabert et al., 2012).<br>D. suzukii produces up to five times more hemocytes than D. melanogaster, making it significantly more resistant to wasp parasitism (Kacsoh and Schlenke, 2012) and making it less likely for indigenous specialized parasitoids to shift host onto it. While parasitization by L. heterotoma induced a decrease in the number of circulating haemocytes in D. melanogaster, it led to a large increase in the total haemocyte counts of D. suzukii (Poyet et al., 2013).<br>The observed difference between the immune response towards L. heterotoma in D. suzukii and D. melanogaster could suggest that European populations of L. heterotoma are not adapted to this new exotic host (Poyet et al., 2013);however, this hypothesis disagrees with the recent observations of a European-wide strain of L. heterotoma that is able to develop and emerge from D. suzukii. (Rossi Stacconi et al., 2013). It is probable that the European-wide strain of L. heterotoma has more effective venom, or that the strain of L. heterotoma used in the original study had lost its ability to develop on D. suzukii because of continued laboratory rearing on D. melanogaster.<br>Pupal parasitoids seem less susceptible to the high hemocyte levels of D. suzukii and they appear to have the highest potential for use in biocontrol of D. suzukii (Kacsoh and Schlenke, 2012). This was confirmed by the successful parasitism rate obtained with a pupal parasitoid by Chabert et al. (2012).<br>The pupal ectoparassitoid P. vindemiae has also been found in association with D. suzukii in orchards and vineyards, both in USA and in Europe (Brown et al., 2011;Rossi Stacconi et al. 2013).<br>Predators of D. suzukii include several species of the bug genus Orius, a generalist predator, which were observed feeding on D. suzukii larvae in backyard raspberries in the autumn of 2009 (Walsh et al., 2011). Preliminary laboratory studies with O. insidiosus (Walsh et al., 2011), O. laevigatus and O. maiusculus (V. Malagnini, personal comm.) indicated that they can feed on D. suzukii larvae infesting blueberries, but their effective control of the pest population have not been proved yet.<br>The activity of microorganisms, as well as the intimate association of the pest species with endosymbionts, has not yet been exploited for biocontrol purpose.<br>Recently, DNA viruses have been isolated in Drosophila species (Unkless, 2011) and were found to be related to other viruses used for pest control.<br>Strains of endosymbiotic bacterium Wolbachia associated with D. suzukii populations have been collected in both the USA and Italy (Siozios et al., 2013;Tochen et al., 2014). These findings suggest the possibility of control of D. suzukii based on pathogens.
Has Cabi datasheet ID
109283
Detection
Detailed morphological description of each stage is given by Kanzawa (1935). A more recently updated description, including references for additional morphological details, is given by Hauser (2011), and another by Vlach (2010), who published a dichotomous key for easy identification. An easy-to-use description of the combination of diagnostic characters that could be used for tentative identification of D. suzukii within its subgroup is given by both Hauser (2011) and Cini et al. (2012). Fruit infestation symptoms are described by Walton et al. (2010).
The dark spots on the male wings together with two sets of black tarsal combs make the identification of the males relatively easy, although the males of some other species do also have wing spots. The wing spots of D. subpulchrella are particularly similar in shape and position to those of D. suzukii. Males without dark wing spots can occur, as it takes two full days before the spots become obvious, although they start to appear within 10 hours of emergence at high temperatures.
The situation is complex for the eggs, larvae and pupae, as no reliable morphological diagnostic features have been identified (Okada, 1968). The eggs of D. suzukii have two respiratory appendages but this character is not species-specific. Instar stages can be estimated by the size of larvae and the colour of the mouthparts, but it is most accurately judged by pre-respiratory ducts (Kanzawa, 1935;Walsh et al., 2011).
Larvae are often undetected inside the fruit. The infested fruits can be detected only by visual inspection under optical magnification (15-20 x magnification). Detection of larvae inside the fruits can also be performed by immersion of fruit samples in sugar or salt solution. Sugar solution can be prepared using approximately 1 part sugar to 6 parts water in order to reach at least 15°Brix. Gently crush the fruits and wait for 10 minutes until the larvae in the sample float to the surface. The same procedure can also be followed using a salt solution, adding 1 part salt to 16 parts water (BCMA, 2013).
Traps baited with different baits have been proposed for detecting adults in the field. Traps can be installed around a site where fruits for shipment are stored, and for early detection in potentially newly-invaded areas, such as near fruit markets, warehouses of food retailers and sites where rotten fruits are disposed. For more information on traps and baits, see the Monitoring and Surveillance section in Prevention and Control.
