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Drosophila surviving Oregon's winter

Scientist scrambling to learn about biology of non-native fly


Capital Press

CANBY, Ore. -- The spotted wing drosophila appears to be doing quite well surviving Oregon's winter -- a fact that comes as no surprise to agricultural scientists.

"We're still catching flies in the field, so the cold weather (in November and December) didn't hurt them significantly," USDA Agricultural Research Service entomologist Denny Bruck said last week.

The fly, which is new to the Northwest, is known to survive winters in Sapporo, Japan, site of the 1972 Winter Olympics, and scientists expected it would survive Northwest winters.

When it comes to other knowledge about the fly, scientists still have more questions than answers.

"Every time we think we know something, we figure out we still have a lot to learn," Bruck said while addressing growers in Canby Jan. 13 at the 56th annual North Willamette Horticulture Society meeting.

Bruck, who is based in Corvallis, is part of a team of scientists in Oregon, Washington and California studying the fly.

The spotted wing drosophila, or suzukii, first appeared in Oregon in 2009. Its numbers escalated in 2010 -- but not to levels some feared.

Some speculated the cold, wet spring of 2010 slowed fly development.

"The odd year may have helped, but it is hard to say. We don't know what normal is," Bruck said.

"Hopefully, it won't be as bad (in the future) as we were all fearing," he said.

The spotted wing drosophila damages fruit by depositing eggs in ripe and ripening fruit. Soft skinned fruit appear particularly susceptible to damage.

Research to date has focused on management options, Bruck said.

Aided by a $5.8 million federal grant, scientists over the next four to five years hope to expand research and learn more about the fly's biology and refine management options, Bruck said.

Scientists also will be monitoring crop losses and treatments to understand the fly's impact on the area's fruit production.

Findings to date indicate that Northwest growers were able to keep losses to a minimum last year, Bruck said.

"Insecticide applications did seem to suppress the insect numbers," Bruck said.

In research trials, pyrethroids, which remained effective 10 to 14 days, provided the best control, followed by organophosphates, which provided 7 to 10 days of control, and spinosyns, which provided 5 to 7 days of control.

Neonicotinoids were relatively ineffective against the fly, Bruck said, providing only 1 to 3 days of control.

Among organically labeled compounds, Entrust, which provided 5 to 7 days of control, was the most effective control agent, Bruck said. It had no residual activity, but was effective as a contact spray and should be considered for resistance management, Bruck said.

Bruck advised growers to target adult flies and to time sprays for early morning or dusk, when flies are most active.

Scientists believe the fly had four generations in Oregon in 2010, Bruck said -- well below the 12 to 13 generations reported in Japan, but consistent with the number of generations scientists expected for the suzukii in Oregon.

Cultural tools that growers should consider include harvesting as soon as possible.

"The longer (the crop) is there, the longer you're going to have to protect it," Bruck said. "If you can shorten that interval at all, you're going to reduce the chance it is going to be effected."

Also, Bruck said, if possible, growers should eliminate wild blackberries and other suzukii host plants from field borders, and clean up after harvest.

"Fruit that falls on the ground can be a resource for flies," he said.

Vinegar fly traps should be placed in shady areas, on the underside of canopies, he said.

"When the spotted wing drosophila appears in your traps, and you have fruit starting to color, that is when we recommend action," he said.

Ultimately, researchers hope to provide growers information on biological control agents. To date, however, the fly apparently has no natural enemies in the Northwest.

Oregon State University entomologist Jeff Miller recently traveled to Japan in the hopes of identifying natural enemies for the fly.


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