Pest of Concern
Infestations of the Spotted Wing Drosophila fly (Diptera: Drosophilidae; SWD), an exotic pest, were found in Oregon fruits. There are 3000 species of Drosophila, commonly known as vinegar flies, but only two have been found to be harmful to crops, of which SWD is one. The SWD can infest and cause a great deal of damage to ripening fruit, as opposed to overripe and fallen fruit that are infested by most of the other Drosophila species. We have just confirmed findings of SWD in blueberries in Philomath, Benton County in Oregon, and have found suspect maggots (larvae) in wild blackberries, red raspberries and some leftover late hanging Marion blackberries east of Corvallis. In addition, maggot samples from the North Willamette Research and Extension Center (Aurora, OR) are also being reared to confirm fly identity. Continued searches for SWD are currently being conducted outside Corvallis over the next weeks. It is crucial to find infestations of this pest as early as possible when they can still be treated effectively. This document makes use of information gathered from both Florida and University of California and USDA Scientists. Several links are provided at the end of this document to aid dissemination of information. This document is based on that information and is being distributed to the Oregon small fruits and grape industries in order to rapidly inform growers, pest management consultants, and extension agents.
Description of Pest
Adult Drosophila flies resemble small fruit or vinegar flies that you may notice buzzing around your kitchen fruit or found around fallen fruit in the outdoors. Typically the well known vinegar flies lay eggs in damaged or decaying fruit, however SWD damage intact ripening fruit. They have a body length of 2-3 mm, with red eyes and a yellowish-brown colored body. The maggots are small (~3 mm) and white-to-cream colored (Figure 3). After maggots mature they may pupate. The pupae are cylinder-shaped, reddish-brown, 2-3 mm in length with 2 small projections on the end. Remember, there are many species of ‘vinegar flies’, so be careful not to mistake it for the common vinegar fly, Drosophila melanogaster, or the western fruit fly, Rhagoletis indifferens, a larger maggot in a different fly family.
Host Range and Potential Impact
These flies are native to SE Asia. Presently, they have been found in California, Florida, Oregon, Washington, and have been established in Hawaii since 1986. This fly attacks a variety of fruits including but not limited to blueberries, blackberries, strawberries, raspberries, cherries, apple, peach, plum, persimmon and Rubus. There is still no proof that the fly attacks grapes, however it has been observed in a lab no-choice food test to oviposit on table grapes and was reported to cause damage to grapes in Japan in the 30’s The SWD lays its eggs within ripening fruit, which makes it an important economic pest to a range of important crops in Oregon.
Infestation of fruit reveals small scars and indented soft spots on the fruit surface left by the female’s ovipositor (“stinger”). The egg(s) hatch in a short time, about 1-3 days, maggots soon begin feeding inside the fruit. Fruit damage is caused by the feeding from maggot development. Within as little as 2 days, the fruit begins to collapse around the feeding site. Thereafter, fungal and bacterial infections and secondary pests may contribute to further damage. These damage symptoms may result in severe crop losses. The implications for exporting producers may also be severe, depending on quarantine regulations.
The SWD is a potential serious pest in Oregon fresh fruit production systems. If you suspect you have SWD in your fruit, it is essential that samples of fruit or adult flies be sent directly to: Jim LaBonte, ODA Plant Division, 635 Capital St. NE , 97391-2532, Salem OR, in order to positively identify adults. This will aid OSU, ODA, and USDA researchers to direct their research efforts during the coming crop season. Your help in this regard is greatly appreciated.