California – For nearly a year, an invisible battle unfolded across backyards, orchards and neighborhoods in and around San Jose. The opponent was tiny, but the possible damage was enormous.
Now, after millions of sterile flies were released and hundreds of properties were inspected or treated, California agricultural officials say the Mediterranean fruit fly has been eradicated from Santa Clara County. A 241-square-mile quarantine established on August 19, 2025, has officially been lifted.
The successful eradication effort was carried out by the California Department of Food and Agriculture, the U.S. Department of Agriculture, the Santa Clara County Agricultural Commissioner’s Office and the Alameda County Agricultural Commissioner’s Office. The infestation was centered in and around the City of San Jose, but the quarantine covered a much wider area to prevent the invasive pest from spreading.
At the center of the response was an unusual but proven strategy: fighting flies with more flies.
CDFA released sterile male Mediterranean fruit flies at a minimum rate of 250,000 flies per square mile each week. Once released, the sterile males mated with fertile females in the environment, but no offspring were produced. Over time, that cycle reduced the wild population and helped bring the infestation to an end.
The flies were supplied through a joint CDFA and USDA sterile insect rearing facility in Los Alamitos. The facility prepares sterile fruit flies every day for release in areas of California where they are needed.
Officials also used targeted treatments close to locations where Medflies had been detected. Properties within 200 meters of detection sites received spot treatments containing an organic formulation of Spinosad. The substance originates from bacteria that occur naturally in soil and was used to eliminate mated females and lower the number of flies in the affected areas.
More intensive action was taken around confirmed breeding populations. At properties within 100 meters of locations where maggots or mated females were found, crews removed host fruits and vegetables that could contain eggs or larvae. That step was designed to interrupt the pest’s life cycle before another generation could emerge.
Those measures required close cooperation from residents. Agricultural officials thanked people in the affected communities for not moving backyard produce and for allowing crews onto their properties to place traps, inspect plants, remove fruit and complete other eradication work.
The Medfly presents a serious threat because it can attack more than 250 varieties of fruits and vegetables. Female flies lay eggs inside produce, where larvae develop and damage the fruit, leaving it unsuitable for consumption. A widespread infestation could affect backyard gardens while also creating severe consequences for California agriculture and the state’s produce exports.
Although the Santa Clara County quarantine is over, officials warned that California remains vulnerable to new introductions of invasive insects. Non-native fruit flies can enter the state through produce carried by travelers, mailed packages or shipments of homegrown food.
Residents are being asked to continue supporting agricultural crews by allowing access for trapping and plant inspections. Travelers entering California from another state or country should avoid carrying fruits, vegetables and other agricultural products. More information about preventing pests from entering the country is available through the Don’t Pack a Pest program.
Officials also advise against mailing or receiving homegrown fruits, vegetables or meat products because invasive species can travel unnoticed inside them. Home gardens should be checked regularly for unusual fruit damage, adult flies or maggots.
Suspected invasive fruit flies can be reported to CDFA at 1-800-491-1899. Additional information about fruit flies and ways to protect California produce is available through the CDFA fruit fly program.
The end of the quarantine marks a major victory, but the campaign is not finished. This infestation was eliminated through sustained scientific work and public cooperation. Preventing the next one will depend on the same partnership.