Drosophila suzukii, commonly called the spotted-wing drosophila, is a vinegar fly—closely related to Drosophila melanogaster (the common vinegar fly). Native to southeast Asia, D. suzukii was first described in 1931 by Matsumura. Observed in Japan as early as 1916 by T. Kanzawa, D. suzukii was widely observed throughout parts of Japan, Korea, and China by the early 1930s. By the 1980s, the “fruit fly” with the spotted wings was seen in Hawaii. It first appeared in North America in central California in August 2008 and is now widespread throughout California's coastal counties, western Oregon, western Washington, and parts of British Columbia and Florida. During the summer of 2010 the fly was discovered for the first time in South Carolina, North Carolina, Louisiana, and Utah. In Fall 2010 the fly was also discovered in Michigan and Wisconsin. The pest has also been found in Europe, including the countries of Italy, France, and Spain.



D. suzukii is a fruit crop pest and is a serious economic threat to soft summer fruit; i.e., cherries, blueberries, raspberries, blackberries, peaches, nectarines, apricots, grapes, and others. Research investigating the specific threat D. suzukii poses to these fruit is ongoing.

Description

Like other members of the vinegar fly family, D. suzukii is small, approximately 2 to 3.5 mm in length and 5 to 6.5 mm in wingspan and looks like its fruit and vinegar fly relatives. Its body is yellow to brown with darker bands on the abdomen and it has red eyes. The male has a distinct dark spot near the tip of each wing; females do not have the spotted wing. The foreleg of the male sports dark bands on the first and second tarsi. The female has a long, sharp, serrated ovipositor. The larvae are small, white, and cylindrical reaching 3.5 mm in length.

When first observed in a new region, D. suzukii has often been confused with the western cherry fruit fly (Rhagoletis indifferens) and was given the short-lasting name cherry vinegar fly. The cherry fruit fly is significantly larger than D. suzukii (up to 5 mm) and have a pattern of dark bands on their wings instead of the telltale spot of D. suzukii. The talltale spot on the wings of male D. suzukii have earned it the common name "spotted wing drosophila" (SWD).

Unlike its vinegar fly relatives which are primarily attracted to rotting or fermented fruit, D. suzukii attacks fresh, ripe fruit by laying eggs under the soft skin. The larvae hatch and grow in the fruit, destroying the fruit's commercial value.

Lifecycle

The lifespan of D. suzukii varies greatly between generations; from a few weeks to ten months. Generations hatched early in the year have shorter lifespans than generations hatched after September. Research shows that many of the males and most of the females of the late-hatching generations overwinter in captivity—some living as long as 300 days. Only adults overwinter successfully in the research conducted thus far. In Washington state, D. suzukii has been observed in association with two exotic and well-established species of blackberry, Rubus armeniacus (syn Rubus discolor) and Rubus laciniatus (the Himalayan and Evergreen Blackberries, respectively.).

Adults emerge from overwintering when temperatures reach approximately 10 °C (268 degree days). The fertilized female searches for ripe fruit, lands on the fruit, inserts its serrated ovipositor to pierce the skin and deposits a clutch of 1 to 3 eggs per insertion. Females will oviposit on many fruits and in regions of scarce fruit, many females will oviposit on the same fruit. In captivity in Japan, research shows up to 13 generations of D. suzukii may hatch per season. A female may lay as many as 300 eggs during its lifespan. With as many as 13 generations per season, and the ability for the female to lay up to 300 eggs each, the potential population size of D. suzukii is huge. It is also important to note that males of D. suzukii become sterile at 30 °C and population size may be limited in regions that reach that temperature.

The larvae grow inside the fruit. The oviposition site is visible in cherries by a small pore scar in the skin of the fruit often called a "sting". After 1 or 2 days, the area around the "sting" softens and depresses creating an increasingly visible blemish. The depressions may also exude fluid which may attract infection by secondary bacterial and fungal pathogens. Pupae may leave the fruit, or remain inside it, to pupate.

Economic Impact

The economic impact of D. suzukii on west coast fruit crops is negative and significantly affects a wide variety of summer fruit in the United States including cherries, apples, blueberries, grapes, nectarines, pears, plums, pluots, peaches, raspberries, and strawberries over a very large geographical area (the coastal regions of western states). Yield loss estimates vary widely, with negligible loss in some areas to 80% loss in others depending on location and crop. Since so little research has been conducted in the affected regions, accurate estimates of damage done by D. suzukii are impossible to ensure. The $500 million actual loss due to pest damage in 2008—the first year D. suzukii was observed in California—is an indication of the potential damage the pest can cause upon introduction to a new location. Future losses may decrease as growers learn how better to control the pest, or may increase as the fly continues to spread.

External links

• http://www.agrotypos.gr/index.asp?mod=articles&id=59309 www.agrotypos.gr regarding D. suzukii
• http://www.agrotypos.gr/images/stories/file/Drosophila.pdf "Georgia-Ktenotrofia" Greek Agriculture Magazine
• http://cemariposa.ucdavis.edu/files/67726.pdf Lifecycle photographs
• http://oregon.gov/ODA/PLANT/IPPM/ General information and control efforts in Oregon
• http://ucanr.org/blogs/blogcore/postdetail.cfm?postnum=1483 Ongoing blog site regarding D. suzukii
• http://swd.hort.oregonstate.edu/ Oregon State University horticulture site
• http://mtvernon.wsu.edu/ENTOMOLOGY/pests/SWD.html Control efforts in western Washington
• http://www.ipm.msu.edu/swd.htm Michigan State University Spotted Wing Drosophila site
• spotted wing drosophila on the UF
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