Mid-Columbia fruit growers and entomologist Doug Walsh aren't sure what to expect this year from a potential new pest -- the spotted wing drosophila.
The fly does not survive hard winters or extreme summer heat, Walsh said.
"We need 105 degrees for a week," he said.
The area did not have a hard freeze this winter, which killed most of the problematic flies in previous years, said Walsh, of Prosser's Washington State University's Irrigated Agriculture Research & Extension Center.
So spotted wing drosophila -- also called the Drosophila suzukii -- were found in April this year, about six weeks earlier than previous years, Walsh said.
At temperatures about 90 degrees, the male D. suzukii goes sterile, Walsh said. That's why one hot week could take care of the pest this year.
The population still is low, but Walsh said he advised some blueberry growers to apply a cover spray for the fly this year for the first time.
At Great Columbia Berry Farm in Burbank, Brandon Lott said they haven't found any spotted wing drosophila, and he won't spray until he does. The farm includes 225 acres of organic blueberries.
If the flies do become an issue, it would be the first major pest problem for local blueberries, Lott said.
So far, the pest has not presented a major problem for any Tri-City fruit growers.
The D. suzukii population remains low during the hot months of July and August. It typically begins to rise in September and October, after most fruit has been harvested, Walsh said.
Last year, most of the drosophila suzukii were found in September, with 1,770 trapped in Benton County. In October, 1,613 were found in traps. Numbers fell to 426 in November, said Luz Barrantes-Barrantes, research associate at WSU Prosser.
However, last month, 47 flies were found in traps, compared with just six in June 2011, she said.
And last July, Barrantes-Barrantes said their traps found a total of 12. This year, 84 flies were caught during the first week of July.
Barrantes-Barrantes said she isn't sure what will happen this year with the pest.
Some cherries showed signs of D. suzukii damage at the packing houses, Walsh said.
When the fly lays its eggs in the fruit, it introduces yeast, which disfigures the fruit, Walsh said. Larvae feed on the yeast, not the fruit.
Walsh isn't sure what the fly will mean for grapes, which have escaped drosophila suzukii damage. He said researchers have tried introducing the flies to Washington wine grapes, but the fly would not lay their eggs in the fruit.
They were able to artificially infest California table grapes, Walsh said. The only difference they could determine was the pH level of 4.5 in the California grapes, while the pH of Washington wine grapes was rarely above 3.0 during the two years of the study, he said.
Washington, Oregon and California received a $4.7 million federal Specialty Crop Research Grant to research D. suzukii. Washington's portion of the 41/2-year grant is about $1 million, Walsh said.
There are 11 species of drosophila found in the Mid-Columbia, but only the D. suzukii damage fruit, Walsh said. They are difficult to identify from the other 10 species.
Males tend to have a spot on each wing, and females have a large ovipositor -- the body part it uses to lay eggs inside fruit, Barrantes-Barrantes said.
The D. suzukii was first identified in Monterey Bay, Calif., in 2009, Walsh said. The fly likely made its way to the United States from southern China or Taiwan -- areas with mild winters.
The next spring later, D. suzukii were first detected in Washington. However, there was a hard freeze in November 2010, during which temperatures reached minus 9 degrees, Walsh said.
"We did not find another fly until the next June," he said.