(Wines&Vines) - The tiny insect pest spotted wing drosophila has cast a large shadow over wine grape growers since 2008, when it was first identified in North America in a patch of strawberries at Watsonville, Calif.

Known scientifically as Drosophila suzukii, the fruit fly was identified among Pinot Noir vines in Oregon’s upper Willamette Valley in 2009, as well as in a non-commercial vineyard south of Abbotsford, B.C.

The fly is frightening because of a jagged ovipositor that allows it to saw into ripe fruit and deposit eggs rather than simply taking advantage of damaged fruit like the better-known species D. melanogaster. Under the right conditions, it is also able to reproduce rapidly—up to 13 generations per season in Japan—though the cooler climate of the Pacific Northwest appears to be limiting its fecundity to as little as four generations per season here.

But a round of research at vineyards across North America are giving growers some hope that the new-found pest—for all its natural equipment—may be as opportunistic as its cousin D. melanogaster with respect to wine grapes.

The relatively thick skins of wine grapes mean most varieties resist penetration by the flies’ ovipositors, reducing the potential for infestations.

While commercial wineries in Virginia found D. suzukii larvae in pressed juice last season, research by Virginia Tech entomologist Doug Pfeiffer notes that damage wasn’t uniform across vineyards and suggests that much may depend on adjacent crops and vineyard-management techniques.

For example, strawberries are a host crop, and flies may head over to ripening wine grapes once berries no longer provide what they need.

Dangers of cross-contamination

Meanwhile, one grower in Virginia lost a third of his crop to sour rot following an infestation—something research by Vaughn Walton, an associate professor at Oregon State University and entomologist attached to the Oregon Wine Research Institute, suggests may be the real risk from D. suzukii infestations.

Research at locations in Oregon and Italy suggest that adult flies carry bacteria that can promote spoilage of fruit damaged by cracking, hail injury and wildlife.

“They’re sitting on those cracked berries and they have bacteria on their mouthparts, on their ovipositors, on their feet, and those body parts get in contact with the exposed pulp on those cracked berries, and that’s what’s causing the issue,” Walton told Wines & Vines. “It’s not the larvae that are causing the issue, it’s these adults that are moving the bacteria around and increasing those spoilage bacteria.”

This isn’t to say ripe grapes aren’t appealing to the flies.