WSU Whatcom County Extension

Integrated Pest Management for Blueberries

Spotted Wind Drosophila

(Drosophila suzukii)

Insects & Invertebrates

 

Spotted Wing Drosophila - Photography by Bev Gerdeman

 

Symptoms

Spotted Wing Drosophila (SWD) is a “vinegar fly” but unlike other vinegar flies, which attack rotting fruit, this fly damages ripening and decaying fruit. Infestation of fruit reveals small scars and indented soft spots and bruises on the fruit surface. Eggs hatch and larvae develop and feed inside the fruit, causing the flesh to collapse around the feeding site within as few as two days. Fungal and bacterial infections and secondary pest may contribute to further fruit deterioration.

 

Spotted Wing Drosophila - Photography by Bev Gerdeman

 

Identification

Adults are small flies (1/16 – 1/8 inch) with red eyes and a pale brown thorax and abdomen with black stripes on the abdomen. The most distinguishable trait of the adult is that the males have a black spot towards the tip of each wing. The females have a large, saw-like ovipositor for inserting eggs into fruit. Larvae are small (1/8 inch), cylindrical and white to cream colored. More than one larva may be found feeding within a single fruit. After maturing, the larvae partially or completely exit the fruit to pupate. The pupae are cylinder-shaped, reddish-brown, and 1/16 – 1/8 inch in length, with two small projections on one end. There are many species of vinegar flies, so one should be careful not to mistake SWD for the common vinegar fly or the Western fruit fly.

 

Spotted Wing Drosophila - Photography by Bev Gerdeman

 

Life History

The life cycle of SWD in the Pacific Northwest is relatively unknown. There are 13 generations per year in Japan and there are predicted to be anywhere from three to ten generations for most of California’s production areas. Like other vinegar flies, this fly does appear to have a short life cycle of one to several weeks. However, this depends greatly on temperature.

Adult flies that emerge in late summer or fall can overwinter (ability to overwinter in the Pacific Northwest is still unknown) and lay eggs during the following summer on early ripening fruit. Females typically will insert their ovipositor into ripe or ripening fruit; lay one to three eggs per fruit, 7–16 eggs per day, and more than 300 eggs in their lifetime. Pupation can take place both inside and outside of fruit. SWD adults are active from April to November and they thrive at cooler temperatures (68˚F); activity, egg laying, and longevity decrease at higher temperatures (above 86˚F). In midseason the adult life span is 3–9 weeks.

 

Spotted Wing Drosophila - Photography by Bev Gerdeman

 

Monitoring

As soon as fruit begins to set, place traps in fields using a 16oz plastic cup containing about ½” apple cider vinegar to determine pest pressure in your area. Monitor traps once or twice per week and record number of adults found. On ripe and ripening fruit, monitor for small puncture (oviposition scar) wounds. Train harvest workers to look for ovipositing symptoms on harvested fruit.

Monitoring techniques are still being developed for this pest.

 

 

Thresholds and Management

This is a new pest to the Pacific Northwest; therefore, thresholds and management strategies are still being developed. Current threshold is detection for this pest. Chemical applications to control adult SWD should be applied when fruit are ripening or ripe.

Consider including sanitation or clean-up practices in your management program when practical. Destroy leftover fruit on the plant to reduce breeding sites and food supplies. Properly dispose of and/or destroy infested fruit that falls on the ground. Work is currently being done to test the efficacy of various sanitation methods including crushing, solarizing, composting, bagging and burying infested fruit.

 

Spotted Wing Drosophila - Photography by Bev Gerdeman

 

References

WSU Whatcom County Extension, Spotted Wing Drosophila
http://whatcom.wsu.edu/ipm/swd/

WSU Mount Vernon NW Research Center, Spotted Wing Drosophila Updates
http://www.mountvernon.wsu.edu/ENTOMOLOGY/pests/SWD.html

Washington State University, Spotted Wing Drosophila Could Pose Threat for Washington Fruit Growers
http://swd.hort.oregonstate.edu/files/files/SWDRelease11-6-09FINAL.pdf

Oregon State University: Extension Service, A New Pest Attacking Healthy Ripening Fruit in Oregon
http://ir.library.oregonstate.edu/jspui/bitstream/1957/13090/1/em8991.pdf

Oregon State University, Current Spotted Wing Drosophila Information for Blueberries
http://swd.hort.oregonstate.edu/current_spotted_wing_drosophila_information_blueberries

 

 

Photography by Bev Gerdeman


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WSU Whatcom County Extension • 1000 N. Forest St., Bellingham, WA 98225 • (360) 778-5800 • whatcom@wsu.edu