Medfly Quarantine in Southern California

Len Wilcox California Corner, Pests


A portion of San Bernardino and Los Angeles counties have been placed under quarantine for the Mediterranean fruit fly (Medfly) following the detection of two wild flies in and around the city of Upland in San Bernardino County. The U.S. Department of Agriculture (USDA), California Department of Food and Agriculture (CDFA), and the San Bernardino and Los Angeles county agricultural commissioners are working collaboratively on this.

The quarantine area measures approximately 95 square miles, bordered on the north by Mount Baldy; on the south by Pomona; on the west by La Verne; and on the east by Chaffey College. CDFA provides an interactive map of the quarantine here.

Sterile male Medflies are scheduled to be released in the area as part of an eradication effort. The release rate will be 250,000 males per square mile, per week, in a 13.28-square-mile area around the infestation. In addition, properties within 200 meters of detections are being treated with an organic formulation of spinosad in order to remove any mated female Medflies and reduce the density of the population. Finally, fruit removal will occur within 100 meters of properties with larval detections and/or multiple adult detections.

The sterile fly release program has a proven track record of success in California. Sterile male flies mate with fertile female flies in the natural environment but produce no offspring. The fly population decreases as the wild flies reach the end of their natural life span with no offspring to replace them, ultimately resulting in eradication of the pest.

Sterile male Medflies are provided by the joint CDFA/USDA sterile insect rearing facility in Los Alamitos, which prepares sterile flies for release every day over the Los Angeles basin. CDFA has successfully eradicated every detected Medfly infestation in California history, dating back more than 45 years.

The quarantine will affect any growers, wholesalers and retailers of susceptible fruit in the area – which includes some varieties of citrus – as well as local residents. Home gardeners are urged to consume homegrown produce on site and not move it from their property.

The Medfly is known to target more than 250 types of fruits and vegetables. Damage occurs when the female lays eggs inside the fruit. The eggs hatch into maggots and tunnel through the flesh of the fruit, making it unfit for consumption. Residents or industry members who believe their fruits or vegetables are infested with fruit fly larvae are encouraged to call CDFA’s toll-free pest hotline at 800-491-1899.

Source: Citrus Pest & Disease Prevention Program

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