D. suzukii adults are 2-3 mm long with red eyes, a pale brown or yellowish brown thorax and black transverse stripes on the abdomen. The antennae are short and stubby with branched arista. Sexual dimorphism is evident: males display a dark spot on the leading top edge of each wing and females are larger than males and possess a large serrated ovipositor.
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.
Related invasive species
- Drosophila suzukii
Related Farm Practice
- Host plants
- Hosts
- Change
- Penetration
- Damage
- Feeding
The fruit fly D. suzukii is a fruit crop pest and is a serious economic threat to soft summer fruit. A polyphagous pest, it infests a wide range of fruit crops, included grape, as well as an increasing number of wild fruits. D. suzukii is an economically damaging pest because the females are able to infest thin-skinned fruits before harvest and the larvae destroy the fruit pulp by feeding. The species is endemic in Asia. It was first recorded as invasive in Hawaii in 1980 and then simultaneously in California and in Europe in 2008. Since 2008 it has spread rapidly throughout the temperate regions of North America and Europe, due to global trade and the initial lack of regulation over the spread of any Drosophila. This species has a high reproductive rate and short generation time;D. suzukii can theoretically have up to 13 generations per year, which may contribute towards rapid spread, given available suitable hosts. D. suzukii is listed on the EPPO alert list.
D. suzukii larvae cause damage by feeding on the pulp inside fruit and berries. The infested fruit begins to collapse around the feeding site causing a depression or visible blemish on the fruit. The oviposition scar exposes the fruit to secondary attack by pathogens and other insects, which may cause rotting (Hauser et al., 2009;Walton et al., 2010).
D. suzukii is predisposed towards infesting and developing in undamaged, ripening fruit. Fruits become susceptible to D. suzukii as they start to change colour, which coincides with softening skins and higher sugar levels (Burrack et al., 2013). There are differences in fruit susceptibility within species and among varieties within the same fruit species (Lee et al., 2011). Fruit penetration force is one potential measure of host susceptibility, but host attractiveness will likely depend upon additional factors, such as soluble sugar content (Burrack et al., 2013). If there is no suitable fruit available, then D. suzukii will attack damaged or deteriorating fruit (Kanzawa, 1935;Lee et al., 2011). Non-commercially marketed fallen fruit or damaged fruit of the following plant hosts may also be attacked: Prunus persica, Malus pumila var. domestica, Prunus triflora, Prunus armeniaca, Pyrus pyrifolia, Pyrus sinensis, Eriobotrya japonica, Lycopersicum esculentum (Kanzawa, 1939) and Rubus microphyllus (Mitsui et al., 2010), as well as over-ripped figs still on the tree (Ficus carica) (Yu et al., 2013).
D. suzukii has been reared from rotting strawberry guava fruits (Psidium cattleianum) collected from trees and on the ground (Kido et al., 1996). It has been observed feeding upon injured or culled fruit including apple and oranges (Walsh et al., 2001).
A recently extensive study on seasonal life cycles and food resources of D. suzukii from low to high altitudes in central Japan (Mitsui et al., 2010) confirmed that D. suzukii emerges almost only from fruits. Some D. suzukii individuals emerged from the fruits of Rubus crataegifolius, Alangium platanifolium, Cornus kousa, Torreya nucifera and Viburnum dilatatum. Grassi et al. (2011) reared D. suzukii also on Prunus laurocerasus and Mann and Stelinski (2011) reported Ribes spp. as host plant of D. suzukii, but this latest observation has not been confirmed in Europe. D. suzukii adults also emerged from the flowers of Styrax japonicus (Mitsui et al., 2010), and in early spring in southern Japan it was also observed to breed on the flowers of Camellia japonica (Nishiharu, 1980).
This field of work is not well described, and so the list of Host Plants and Other Plants Affected contains probable as well as reported hosts.