Spotted wing drosophila

Drosophila suzukii

Adults and maggots closely resemble the common vinegar fly, D. melanogaster, and other Drosophila species that attack primarily rotting or fermenting fruit. Spotted wing drosophila, however, readily attacks undamaged fruit. See IdentifyingDrosophila suzukii in References for help with distinguishing this pest from other flies. The online version of this publication also includes a link to an SWD identification card.
Adults are small flies about 1/16 to 1/8 inch long with red eyes and a pale brown thorax and abdomen with black stripes on the abdomen. The most distinguishable trait of SWD males is a black spot towards the tip of each wing. The females do not have spots on wings but have a very prominent, sawlike ovipositor for laying eggs in fruit.
Larvae are tiny, white cylindrical maggots a little longer than 1/8 inch when full grown. One to several larvae can be found feeding within a single fruit. After maturing, the larvae partially or completely exit the fruit to pupate.
Spotted wing drosophila may be mistaken for other adult flies and maggots. Look closely by comparing anatomical features of the maggots and wing patterns of adult flies. For instance, adult Western cherry fruit flies, Rhagoletis indifferens, in another family of flies called Tephritids, are much longer at 3/16 inch than SWD adults and have a dark banding pattern on their wings. This fruit fly, which is a quarantine pest, occurs in Washington, Oregon, and other states but has not established in California. If you suspect you have a Western cherry fruit fly, take specimens to your local agricultural commissioners’ office.
Research studies to define the biology and life cycle of SWD in California are still underway; however, like other vinegar flies, it appears to have a short life cycle of one to several weeks depending on temperature and can have as many as 10 generations per year. This rapid developmental rate allows it to quickly develop large populations and inflict severe damage to a crop.
In its native Japan and in coastal California the adult flies can be captured throughout much of the year. In California’s inland valleys the adult flies are most active during spring and fall when highs are between 60 and 80 F, especially when conditions are humid and food is available. In laboratory studies at constant temperatures, they are most active at 68 F; activity becomes reduced at temperatures above 86 F.

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