A new exotic pest, the European grapevine moth, is damaging grape clusters in the Napa Valley, raising concern among farmers and sparking a hunt to learn the extent of the infestation.

The moth larvae found in an Oakville-area vineyard is the first known infestation in the United States, officials announced Monday. As a result, agricultural inspectors are setting out traps in both Napa and Sonoma counties.

?If it did get here, it could be pretty damaging,? said Nick Frey, president of the Sonoma County Winegrape Commission. ?So it certainly is a concern to growers.?

The moth, Lobesia botrana, can feed on the flower or the fruit of the grapevine. If the pest attacks mature grape clusters, the berries can become further damaged through infection of botrytis, also known as bunch rot.

On Monday inspectors were checking special traps spread over a 9-square-mile area of Napa County to ?very quickly figure out how widespread this thing might be,? Napa County Agricultural Commissioner Dave Whitmer said.

The moth?s presence was confirmed by a state laboratory last week, Whitmer said. Scientists took the insect at the pupa stage and allowed it to turn into an adult moth.

?We may well be talking about some type of quarantine,? Whitmer said, but it was too early to know how the California Department of Food and Agriculture and the U.S. Department of Agriculture would address the infestation.

Spokespersons for those two agencies were unavailable for comment Monday.

The moth, Whitmer said, has shown ?it can create a problem? in areas with climates similar to Northern California.

The moth has damaged berries and berry-like fruit in Europe, the Mediterranean, southern Russia, Japan, the Middle East, Near East and northern and western Africa, officials said. Besides grapes, the pest can feed on such plants as olives, blackberries, cherries, nectarines, persimmons and pomegranates.

Sonoma County Agricultural Commissioner Cathy Neville said her office is assisting in the hunt for the moth.

?We?re working with CDFA and USDA to put traps out to see if we have it here,? Neville said.

The European grapevine moth is part of the same ?Tortricidae? family as the light brown apple moth, Whitmer said. That pest, which is native to Australia, was first confirmed in California in 2007 and has prompted a $75 million eradication program.

For the apple moth, the trapping of two adult male moths within three miles of one another is enough to prompt a quarantine. Such quarantines remain in effect in at least 16 California counties, including Sonoma and Napa.

Under the quarantines, farmers still may move grapes or other produce to market, but they must demonstrate that doing so won?t spread the infestation.

A 2003 report on the European grapevine moth concluded that California?s wine-producing counties of Napa, Sonoma, Amador, Monterey and San Louis Obispo may be suitable habitat for the pest. Roughly three-tenths of the U.S. potentially could become home to the moth, including a large swath of the East from Louisiana to Maine.

The report rated the potential economic impact from an infestation as ?high.? The pest?s larvae ?can seriously affect the mature grape berry harvest,? according to the report by scientists from the University of Minnesota.

Since 1984 federal inspectors have discovered only 20 such moths, largely associated with international airline passengers, researchers wrote.