Non-native fruit fly adapts to cold weather in Idaho

More than three years after Moscow resident Dylan Champagne first found an infestation of the non-native spotted wing drosophila in his backyard cherry crop, extension entomologists at the University of Idaho are still discovering more unique attributes of the havoc-wreaking vinegar fly.

Entomologist Stephen Cook, also a faculty member at UI, has been trapping the red-eyed insects on a regular basis and was surprised to find mid-November’s cold weather – with temperatures dropping into the teens – didn’t leave his traps empty.

At the end of October, Cook reported he and southern Idaho cohort Jim Barbour trapped upward of 4,000 spotted wing drosophila, and while numbers dropped off, stragglers in the double digits remained past Thanksgiving.

This discovery takes experts a step closer to understanding how the insects handle changing seasons.

“We do have a lot of insects that survive well into the fall as adults,” Cook said. “Different insects handle cold temperatures differently.”

Some of these ways seem straight out of a science fiction novel.

“They typically do one of two things. They try and change all of their body fluids to water and they’ll freeze and stay frozen. As soon as it thaws, they thaw and are active. The other thing they do is the opposite of that. They fill their body with an antifreeze and so they try to remain unfrozen,” Cook said. “It’s not the cold that is hard on insects – it’s the freezing and thawing, so they try to either freeze and stay frozen or they try not to freeze at all.”

The spotted wing drosophila is still new enough to North America that little is known about it. Native to China and Japan, the pest was first found in California in 2008 when it damaged strawberry crops. It was identified in Idaho in summer 2012.

The most unusual trait researchers have found about the spotted wing drosophila so far is its ability to burrow into and destroy decomposing or fallen fruit, or fruit that is still in development.

“The oddest thing about this fruit fly from a North American perspective is we don’t have any fruit flies that posit into fresh fruit, into developing fruit that’s still on the vine or tree. This one does that. It lays its eggs inside the fruit as it’s developing, so you don’t even see the damage until the fruit starts to shrivel up and the insect emerges,” Cook said.

While its fruits of choice are typically soft ones, such as Himalayan blackberries, strawberries, peaches and plums, the insect is also capable of benefiting from any damage to a hard or tough-skinned fruit to creep inside and lay its eggs.

Cook said researchers have recently discovered the pesticide commercial orchardists use on their trees is effective against the damaging flies, but they aren’t sure whether the flies are simply relocating while the spray is in effect and returning to reinfest later.

Cook said backyard growers should keep an eye on their soft fruits for signs of damage by the flies.