During the last two months, this office has had many samples of strawberry and raspberry fruit infested with fruit fly larvae submitted. What has been notable about this species of fruit fly is that it is infesting maturing fruit, rather than over-ripe and rotten fruit, as is the case with the vinegar fly that we are all accustomed with.
These new fruit flies found this fall have been found in very high numbers in strawberry and caneberry fields northeast of Watsonville.
The new species of fruit fly is Drosophila suzukii (misidentified in November 2008 as Drosophila biarmipes). Adults of this fruit fly found are almost identical to the regular vinegar fly, Drosophila melanogaster, with the exception that the males have one black spot on the back portion of each wing.
I have submitted samples to the California Department of Pesticide Regulation and found that this fruit fly is not new to California. It is categorized as a Class ‘C’ pest and is not subject to any exceptional regulatory scrutiny.
It is imperative that growers look for this fruit fly early on next year, and take steps to control it early, before it becomes a pest of the proportions it has been this year.
It is advisable not to leave strawberries and caneberries to continue to fruit without harvest over the winter, as it is suspected that the D. suzukii will continue to breed and multiply in these areas. Having large numbers of this pest overwinter will only exacerbate problems next year.
While the embedded larvae are not controlled short of destroying the fruit, the adults are relatively easy to control with pesticides. Malathion is effective for conventional growers, and Pyganic is very effective for organic growers. Since only the adults are being controlled with pesticide applications, multiple applications spaced 7 to 10 days apart will probably be best for long term control.
There are several insecticides mentioned for control of fruit flies in this article. Before using any insecticides, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.
Drosophila biarmipes on raspberry fruit.
Mating pair of Drosophila biarmipes.
Drosophila biarmipes in trap. Note how easily visible the black spot is on individual male flies.
Two Drosophila biarmipes larvae embedded in a raspberry fruit. They are the long white objects in the center of the photograph.