Flies in a bottle

WENATCHEE, Wash. – In the course of a single year, a tiny insect has been damaging tree fruit around the globe. Spotted wing drosophila, or SWD, a type of vinegar or fruit fly, has been known in Japan, its home turf, for decades.

The fly was first detected in the United States in California in 2008 and quickly spread northwards into the Pacific Northwest.
“Most drosophilids don’t attack undamaged fruit — indeed the vast majority cannot — but this one can,” said Elizabeth Beers, an entomologist and Extension specialist based at WSU’s Tree Fruit Research and Extension Center in Wenatchee.
“The female has a saw-like ovipositor and lays her eggs in the flesh of the fruit. Larvae hatch, feed and tunnel, turning fruit into a gooey mess,” Beers said. “The fly can be devastating, but we rapidly developed controls. We now have a basic pest management strategy that is being fine tuned.”
“This is a temperate-climate pest,” Beers explained, “but it seems to be adapting to our dry eastern Washington climate. So we have to discover its ecology in these arid and semi-arid regions. As predicted, it likes the maritime climate west of the Cascades.”
Beers looks for SWD

The management strategy for SWD consists of a couple main components, Beers said. The first step is vigilance. Members of the Washington SWD detection team are driving about 1,200 miles per week to hang and retrieve traps baited with apple cider vinegar. “When we catch one fly in a region, we warn people with susceptible crops and recommend they use continuous pest protection until harvest,” Beers said.

The other component is to understand the fly’s phenology — that is, how and when it develops in eastern Washington’s climatic conditions and, from there, when it begins attacking fruit. “I don’t think we’ve ever gathered this much data so quickly on a pest in eastern Washington,” Beers said of the effort so far. The control efforts in Washington are part of a larger, West Coast-wide study to understand and control the pest. Scientists in California, Oregon and British Columbia are also on the management task force.
The goal is to minimize the need to spray pesticides, Beers said. “For now, we must err on the side of caution until we nail that down.” The regional team is also looking for a biocontrol, a good bug that will prey on the fruit fly. “A couple parasitoids have been found that attack the pest,” Beers said.
Apple cider vinegar used as bait

Another possible management technique under investigation is sanitation. As Beers pointed out, “Any Drosophilid can attack damaged fruit. SWD just has a couple weeks head start. Keeping fruit off the floor may lower pressure, but so far that is just a theory.”

“We’ve got over 300 traps per week coming in here,” Beers said, “with more going to WSU entomologist Doug Walsh’s lab in Prosser.” Only a few of the traps have contained SWD, but if they do, that information will be updated in real time on the management task force’s website.