The cherry fruit fly, a pest that could threaten a variety of commodities, has turned up in parts of Northern California.

“It’s quite possibly going to be a headache for fruit growers,” said Don Mayeda, deputy agricultural commissioner for Merced County.

The cherry fruit fly is a drosophila, a genus of very small flies, most of which are harmless, he said.

A grower and a pest-control advisor brought the fly to the attention of Bill Coates, a University of California Cooperative Extension farm adviser for San Benito, Santa Cruz, Santa Clara and Monterey counties on May 14.

“I set out traps and, within 24 hours, specimens were shipped to the California Department of Food and Agriculture for identification,” he said.

Tiny holes — or stings — on the skin of the cherries and maggots in the flesh of the fruit tipped off the grower, Coates said.

The difference between the cherry fruit fly and others of the genus is that the cherry fruit fly is able to pierce the skin of soft fruit to lay its eggs, he said.

The discovery of the pest comes just as the harvest of bing cherries, California’s dominant cherry variety, is ramping up.

So far, the pest is in only a handful of counties and infestation has been limited to cherry orchards, but it could threaten other commodities.

“Once the cherries are gone, they’re going to move into other soft fruit,” said Tim Pelican, deputy agricultural commissioner for Stanislaus County.

Coates said he has learned the fruit fly began to appear in some coastal strawberry fields last summer.

“With the number of counties that this is in, I think it has been around for a while and was only a minor pest until it developed population levels to blow up,” Coates said.

The Department of Food and Agriculture and county agricultural commissioner staffs are trying to determine the best traps to use to track the bug, he said.

“These flies are so small that it’s difficult to tell a nonpest drosophila from a pest drosophila, and the traps will catch both,” Coates said.

Adding to the dilemma: The number of nonpest drosophilas found in a trap can exceed the number of cherry fruit flies as much as 100 to one, he said, and a black spot on the wings of male cherry fruit flies is the only difference between the pest and other benign species.

Nonpest species, known commonly as vinegar or nuisance flies, are often found on and around rotting fruit and even in kitchens when a banana becomes too ripe, he said.

“This is a brand new insect for us,” Mayeda said. “We don’t know how widespread it is.”

The Department of Agriculture has alerted all county agricultural commissioners’ offices to be on alert for the fruit fly to help determine the extent of the infestation and to help decide what steps must be taken to eradicate the pest.

Several registered pesticides can wipe out the fly, Mayeda said.