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Researchers try to swat red-eyed vinegar fly

A team of Washington State University researchers is swatting back at a species of Asian fruit fly that threatens the state's lucrative fruit-growing industry.

Researchers in Prosser, Mount Vernon and Wenatchee are using a $1.2 million U.S. Department of Agriculture grant to trap, study and test pesticides to combat the spread of spotted wing drosophila, a type of red-eyed vinegar fly.

Vinegar flies are common in the state, but this particular bug is dangerous to crops because females have a larger-than-average egg injector, said Doug Walsh, an entomology professor at the WSU Irrigated Agriculture Research and Extension Center in Prosser.

Most vinegar flies have smaller egg injectors, called ovipositors, and only can lay eggs in fruit that's soft and rotting -- the kind no human wants to eat.

But the larger ovipositor on spotted wing drosophila means they can lay eggs in ripening fruit and spoil cherries or berries before they go to market.

"Most people aren't too thrilled about maggots in their produce," Walsh said.

The flies came from Asia -- Japan, Korea and China -- and were introduced into California in 2008, likely through produce imported from Hawaii, he said. They since have migrated up the Pacific Coast to Oregon and Western Washington.

The pest is known to attack cherries, raspberries, blackberries, blueberries, strawberries, plums, pluots and nectarines.

According to data from the state Department of Agriculture, cherries are one of the state's top 10 commodities and brought in $297 million in 2008, the last year for which data was available.

On the west side, researcher Lynell Tanigoshi, an entomologist at the WSU Northwestern Washington Research and Extension Center in Mount Vernon, is testing pesticides that can kill spotted wing drosophila without threatening pollinating honey bees.

Tanigoshi also is working with extension educators to inform fruit growers about monitoring and control programs.

Walsh is working with entomologists and educators to monitor for the fly in Eastern Washington. So far none of the pests has been caught in traps here, and Walsh hopes that never will happen.

He said the flies like a more temperate climate such as that found along the coast. They like temperatures between 50 and 85 degrees, especially weather that's mild and wet.

"This is a fair-weather bug," Walsh said. "When we look at developing models, the Skagit Valley is kind of its ideal climate range."

The dry climate in Eastern Washington, coupled with its cold winters and hot summers, could stem the spread of spotted wing drosophila on this side of the mountains.

Fruit growers have their fingers crossed the flies don't cross the mountains.

B.J. Thurlby, president of the Washington State Fruit Commission, said he's following the WSU research and hoping the pest can be managed if it turns up in Eastern Washington.

"It has the potential to pose problems if we have a breakout," he said. "What we're trying to do today as an industry is build a network of people in the know that would allow us if this bug does show up to know right away and have a comprehensive industry plan for it."

-- Michelle Dupler: 582-1543; mdupler@tricityherald.com

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