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SACRAMENTO, March 10, 2026 – A portion of San Diego County has been placed under quarantine for the Mexican fruit fly following the detection of five flies including a mated female within the City of La Mesa. The United States Department of Agriculture (USDA), the San Diego County Agricultural Commissioner, and the California Department of Food and Agriculture (CDFA) are working collaboratively on this project.
The quarantine area in San Diego County measures 77 square miles, bordered on the north by the San Diego River; on the south by Sweetwater Reservoir; on the west by Interstate 15; and on the east by El Cajon. A link to the quarantine map may be found here: www.cdfa.ca.gov/plant/mexfly/regulation.html.
Sterile male Mexican fruit flies will be released in the area as part of the eradication effort. The release rate will be approximately 250,000 males per square mile per week in an area up to 50 square miles around the infestation. Sterile male flies mate with fertile female flies in the natural environment but produce no offspring. The Mexican fruit fly population decreases as the wild flies reach the end of their natural life span with no offspring to replace them, ultimately resulting in the eradication of the pest. Properties within 200 meters of detections are being treated with an organic formulation of Spinosad, which originates from naturally-occurring bacteria, in order to remove any mated female fruit flies and reduce the density of the population. Finally, fruit removal will occur within 100 meters of properties with larval detections and/or mated female detections.
The quarantine will affect growers, wholesalers, and retailers of susceptible fruit in the area as well as nurseries that grow and sell Mexican fruit fly host plants. The quarantine will also affect local residents – home gardeners are urged to consume homegrown produce on site and not move it from their property. These actions protect against the spread of the infestation to nearby regions where it could affect California’s food supply and our backyard gardens and landscapes.
The Mexican fruit fly can lay its eggs in and infest more than 50 types of fruits and vegetables, severely impacting California agricultural exports and backyard gardens alike. For more information on the pest, please see the pest profile at: www.cdfa.ca.gov/plant/go/MexFly. Residents who believe their fruits and vegetables may be infested with fruit fly larvae are encouraged to call the state’s toll-free Pest Hotline at 1-800-491-1899.
The eradication approach used in the La Mesa area of San Diego County is the standard program used by CDFA and it is the safest and most effective and efficient response program available.
While fruit flies and other invasive species that threaten California’s crops and natural environment are sometimes detected in agricultural areas, the vast majority are found in urban and suburban communities. The most common pathway for these invasive species to enter our state is by “hitchhiking” in fruits and vegetables brought back illegally by travelers as they return from infested regions of the world. To help protect California’s agriculture and natural resources, CDFA urges travelers to follow the Don’t Pack a Pest program guidelines (www.dontpackapest.com).
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