Fruit pest survives winter
Entomologist: Warm spell may mean more spotted wing drosophila
By DAN WHEAT
WENATCHEE, Wash. -- If there's one thing Elizabeth Beers is learning about spotted wing drosophila in Central Washington it is to expect the unexpected.
The Washington State University entomologist was surprised this winter when a pair of spotted wing drosophila, male and female, showed up in a trap in a Mattawa cherry orchard in January. They landed there after the trap was checked in December.
Winter is harsh enough in Central Washington that spotted wing is suppose to be laying low.
"It's not true hibernation but it's cold enough they don't usually move," said Beers who works at the WSU Tree Fruit Research and Extension Center in Wenatchee.
In warmer California, spotted wing operate 12 months of the year and they are much more active in Western Oregon and Western Washington in winter than east of the Cascades, she said.
Mattawa and the Tri-Cities are the warmest parts of the state and a warm spell of temperatures into the 40s probably prompted the pair to be on the move, Beers reasons.
What it means, she said, along with a mild winter, is that spotted wing may have wintered over better and will increase this spring and summer in cherry orchards.
But she's not dogmatic about that because last year she believed there would be a big increase and there wasn't.
In November 2010 she was surprised when 6,539 spotted wing drosophila flies were trapped in a cherry orchard near Royal City. It was 40 times greater than the norm of all traps in Central Washington in October, which had been a heavy month.
WSU researchers trapped 60,381 spotted wing drosophila in Central Washington in 2010 and expected more in 2011. They doubled their trapping but collected just 13,807 flies, 90 percent fewer when corrected for the number of traps and frequency they were checked.
"The most logical explanation is the pre-Thanksgiving Day freeze of 2010 and the cool, wet spring of 2011 knocked it back enough that it never really took off," Beers has said.
Beers and Doug Walsh, WSU entomologist in Prosser, maintained 46 traps through this past winter, checking them once a month in the coldest months, now every other week and soon every week.
They had 690 traps in 2011 and plan to have a similar level this season.
An Asian pest first detected in the U.S. in California strawberries in 2008, spotted wing drosophila damaged cherries there and spread north into Western Oregon and Western Washington damaging berries.
It was discovered in Eastern Washington June 28, 2010 and was found in the largest numbers, on average, near the north central Washington towns of Orondo, Wenatchee, Tonasket and Quincy.
The biggest threat has been to cherry growers. Spotted wing drosophila doesn't seem to like the acidity of grapes nor the thick skin of pears and apples.