The spotted wing drosophila fly, which lays its eggs in fruit and makes it unmarketable, could reach record population levels in the Pacific Northwest this year, according to Oregon State University researchers. 

"All indications estimate this season will be similar or worse than 2012, which was the worst on record," said Vaughn Walton, an entomologist with the OSU Extension Service. “Winter and spring temperatures in the Pacific Northwest have been warmer than last year, and heat equals larger populations of spotted wing drosophila.”

Originally from Asia, the spotted wing drosophila was first found stateside in California in 2008 and has since spread across the continent. The insect lays its eggs in ripe and ripening small and stone fruits, and its developing larvae eat the fruit. The cosmetic imperfections caused by the larvae make the fruit undesirable to most consumers.

The fly's favorite fruits include blueberries, cherries, blackberries, raspberries, peaches and plums. The pest has not impacted wine grapes so far, Walton added.

Walton expects spotted wing drosophila populations in the Pacific Northwest to rapidly build through July and August when most susceptible fruits ripen.

The economic stakes are high. In Oregon alone, farmers grew $198 million of berries in 2012, with blueberries accounting for $108 million of that, according to a report by the U.S. Department of Agriculture. Growers also sold $74 million of sweet cherries that year, the report said.

In the absence of detection and control measures, Oregon's small and stone fruit industry could lose $31 million per year, according to a report by the Giannini Foundation of Agricultural Economics at the University of California.

 

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Since the discovery of the pest in Oregon, OSU has been collaborating with scientists in California and Washington to better understand it and help growers deal with it. For example, researchers at OSU are seeing if a parasitic wasp that is native to the United States, known as Pachycrepoides vindemmiae, can be used to control the spotted wing drosophila. It lays its eggs in the fly's pupae, thus killing them.

OSU will also lead a trip to South Korea in August to search for and collect other similar wasps, including one known as Asobara japonica that lays its eggs in the spotted wing drosophila's larvae. Over the next few years, researchers will study these wasps in quarantine to determine if it attacks only the fly's larvae. If tests show the wasp does not harm other insects, Asobara japonica and others could be released in the U.S. in three to five years.

For now, OSU has found that insecticides are the best way to control the pest. OSU pesticide evaluator Joe DeFrancesco tested various compounds for use on strawberries, blueberries and caneberries to see which are most effective. OSU entomologist Peter Shearer has conducted similar work on cherries. The top-performing pesticides are on OSU's website at http://bit.ly/SWD_GrowerInfoOSU.