Parts of Contra Costa and Santa Clara counties are under quarantine for the oriental fruit fly after the discovery of multiple flies in each county, according to a statement from the California Department of Food and Agriculture.

In Contra Costa County, detections near Brentwood and Oakley resulted in a quarantine zone covering 99 square miles, bordering the San Joaquin River to the north, Marsh Creek State Park to the south; Black Diamond Mines Regional Preserve to the west, and Old River to the east.

An oriental fruit fly is shown in an undated image from video. Recent discovery of the fly in Contra Costa and Santa Clara counties has prompted the California Department of Food and Agriculture to declare quarantines in those areas. (CDFA/YouTube)

Detections in Santa Clara County cities of Santa Clara and Sunnyvale have resulted in a quarantine zone covering 112 square miles, bordering Coyote Creek to the north; Saratoga to the south; Mountain View to the west, and Alum Rock to the east.

The quarantine maps can be found online.

“Invasive fruit flies are serious pests for California’s orchards and backyard gardens,” said CDFA Secretary Karen Ross. “These recent detections remind us that we need to remain vigilant in protecting our food supply and natural resources.

“The stakes are enormous, and not just in California. A new report from the United Nations notes that invasive species management costs hundreds of billions of dollars each year around the world,” Ross said. “We’re all in this together as we work to reduce this impact. “

Hundreds of crops at risk

The oriental fruit fly is known to target more than 230 different fruit, vegetable, and plant commodities. California crops at risk include grapes, pome, stone fruits, citrus, dates, avocados, and many vegetables, particularly tomatoes and peppers.

Damage occurs when the female fruit fly lays eggs inside the fruit. The eggs hatch into maggots, which tunnel through the flesh of the fruit or vegetable, making it unfit for consumption.

Residents in quarantine areas are urged not to move those items from their property. However, they may be consumed or processed (I.e., juiced, frozen, or cooked on the property where they were picked) or disposed of by double bagging and placing in the regular trash, not green waste.

Agricultural officials use “male attractant” technique as the mainstay of the eradication effort for this invasive species, an approach that eliminated dozens of fruit fly infestations in California. Workers squirt a small patch of fruit fly attractant mixed with a very small dose of an organic pesticide, spinosad, approximately 8-10 feet off the ground on street trees and similar surfaces. Male fruit flies are attracted to the mixture and die after consuming it.

YouTube video
A primer on spinosad and how it is used to treat fruit fly infestations. (California Department of Food and Agriculture/YouTube)

The treatment program is being carried out over an area that extends 1.5 miles from each site where the oriental fruit flies were trapped.

The most common pathway for these pests to enter the state is by “hitchhiking” in fruits and vegetables brought back illegally by travelers as they return from infested regions of the world or from packages of homegrown produce from other countries sent to California.

The Don’t Pack A Pest website features more information about not transporting pests when traveling or mailing packages.

The oriental fruit fly is widespread throughout much of the mainland of southern Asia and neighboring islands, including Sri Lanka and Taiwan, and it has infested other areas, most notably Africa and Hawaii.

For questions about the project, call CDFA’s pest hotline at 800-491-1899. More information about the oriental fruit fly is available online.