An Unwelcome Visitor

09/01/2009 02:00:00 AM
Vicky Boyd

A fruit fly, which prefers maturing fruit over decaying fruit, has growers in at last three states on edge as it came on the scene in May and began causing significant damage to central California cherries and berries.

The spotted wing drosophila entered the spotlight this summer when growers along the California coast noticed bruise-like damage to strawberries and caneberries and puncture holes in cherries.

It has been found in nearly two dozen California counties as well as two counties in Washington state and on two residential properties 3 miles apart in Hillsborough County, Fla.

Identifying features

At 2 to 3 millimeters, the spotted wing is about half the size of the Western cherry fruit fly, which is a quarantine pest in Washington but has not been found in California.

Photo by Ed Snow
The spotted wing drosophila fruit fly has been confirmed in California, Washington and Florida.

Nearly all of the 3,000 species within the drosophila fruit fly group prefer decaying fruit on which to lay their eggs. But the spotted wing likes fruit that’s just beginning to mature.

Initially, the pest was called the cherry vinegar fly. But that has been changed to spotted wing drosophila—scientifically known as Drosophila suzukii—to avoid confusion with other vinegar fruit flies.

Damage is caused when the female pierces the skin’s fruit with a serrated ovipositor to lay eggs. In cherries, the ovipositing hole may be visible, but in strawberries it’s not, according to Mark Bolda, a University of California Cooperative Extension farm adviser specializing in berries in San Benito, Santa Cruz, Santa Clara and Monterey counties.

As the larvae feed internally on strawberries, bruises and soft spots develop that pickers should recognize as defects to cull.

The openings also can provide entryways for secondary disease organisms.

The pest is C rated in California, meaning the state will not quarantine an area or impose control measures should one be found, says Norm Smith, an entomologist with California’s Fresno County Agriculture Commissioner’s office. The only restriction is plant material must be apparently free of the fruit fly before transport.

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