Spotted Wing Drosophila Fly Populations Mount In Pacific Northwest

This could be worst season for the pest yet.

Published on: May 22, 2013

An alarm is ringing for fruit growers in Oregon and Washington to be on the alert for signs of bigger infestations of the dread spotted wing drosophila fruit fly this season.

"The bottom line is that we have found the bugs in relatively higher numbers than last season in the field, and our lab models indicate that conditions have been right for a larger number of the flies to hatch this year," says Vaughn Walton, Oregon State University Extension entomologist.

Using a population computer model showing under which climate conditions populations of the fly may expand, Walton says this could indeed be a bad year for fruit growers in the two states.

The model reproduces environmental conditions which can trigger higher populations of the pest which debuted nationally in California in 2008, and spread quickly across other parts of the U.S.

Spotted wing drosophila flies like this one could be breeding up some challenging populations for fruit producers this year, a WSU entomologist warns.
Spotted wing drosophila flies like this one could be breeding up some challenging populations for fruit producers this year, a WSU entomologist warns.

In absence of detection and control measures, Oregon's small and stone fruit growers could lose more than $30 million a year to the pest, according to reports from the University of California's Giannini Foundation of Agricultural Economics.

What growers should do is keep a close eye on their crops once they begin to change color and ripen, advises Walton, since it is at that stage that the first fruit infestations become visible.

"Live traps in the Willamette Valley (Oregon) and Washington's Columbia Basin have been turning up more of the flies, but those traps are not always a good indication of what is happening to population levels," he notes.

However, the traps do offer growers a good idea of what fruit fly activity is taking place in their region, adds Walton.

The fly is particularly fond of some of the PNW's most prolific fruits, including blueberries, cherries, blackberries, raspberries, peaches and plums.

"We do not have an indication yet of whether the populations may grow in Idaho," says Walton.