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Spotted wing drosophila detected in SW Idaho

An exotic fruit fly that was first detected in Idaho in 2012 appears to have gained a tentative foothold in the state and researchers are trying to determine how widespread it is.
Sean Ellis

Capital Press

Published on June 23, 2015 1:12PM

CALDWELL, Idaho — University of Idaho researchers have alerted fruit growers in Southwestern Idaho that they are finding small numbers of spotted wind drosophila, an exotic fruit fly that attacks a wide range of fruit.

Low numbers of the pest have been found in traps in Payette, Canyon and Owyhee county orchards, said Jim Barbour, an entomologist at UI’s Parma research station.

But the flies reproduce quickly, so growers should monitor susceptible crops frequently, he said.

“We are finding them, but not in significant numbers,” Barbour said. However he added, “they can really reproduce quickly and their numbers can get quite high pretty quickly.”

Unlike the common cherry fruit fly, which attacks ripe or already damaged fruit, the spotted wing drosophila can lay eggs in much firmer and thicker-skinned fruit still attached to the plant.

It also has a broader range of hosts than other fruit flies, from berries, cherries and grapes to plums and peaches.

Large commercial orchardists said they are concerned about the pest because of its potential to cause widespread damage, but they haven’t yet seen any damage from the flies.

“So far, it hasn’t been an issue, but it’s definitely something we’re keeping an eye on,” said Chad Henggeler, field manager for Henggeler Packing Co., one of Idaho’s largest orchards.

The fly was first detected in small numbers in Idaho in 2012 and hundreds of them were detected in traps in 2013. Few of the insects were detected in 2014.

Researchers initially hoped that they were brought here accidentally and wouldn’t survive Idaho’s harsh winters, Barbour said.

Southwestern Idaho, where the majority of the state’s fruit is grown, is marginal habitat for the drosophila, which doesn’t like the cold and dry conditions prevalent in this region.

Researchers now believe the insects are over-wintering in the area but their winter survival rate is low, Barbour said.

“They’re here and they’re probably not going to go away,” he said. “But at the numbers they are occurring at now, they’re probably not hurting anyone.”

UI researchers received a grant that will enable them to do some systematic testing to determine how widespread the flies are and how much of a problem they are causing, Barbour said.

Between Southwestern Idaho’s harsh winters and desert conditions, “they shouldn’t do that well here most years,” he said. “But it will take a few years of monitoring for us to sort that out.”


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