SACRAMENTO, August 4, 2025 – The California Department of Food and Agriculture (CDFA), the United States Department of Agriculture (USDA) and the Alameda County Agricultural Commissioner’s office have eradicated a Mediterranean fruit fly (Medfly) infestation centered in and around the City of Fremont, ending a 213-square-mile quarantine that began September 6, 2024.
CDFA used the release of sterile male Medflies at a minimum rate of 250,000 flies per square mile per week as the primary eradication measure for this pest. Additionally, properties within 200 meters of the detection sites were treated with an organic formulation of Spinosad, which originates from naturally-occurring bacteria in soil, to eliminate any mated females and reduce the density of the population.
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 the eradication of the pest. The sterile male Medflies are brought to California by the joint CDFA/USDA sterile insect rearing facility in Los Alamitos, California, which prepares sterile flies for release everyday over portions of California.
USDA, CDFA, and the Alameda County Agricultural Commissioner acknowledge and thank local area residents for their cooperation in preventing the movement of backyard fruit and allowing property access to perform critical eradication activities. Working together, we rid California of this invasive species.
“Fruit flies are very destructive pests for crops as well as backyard gardens,” said CDFA Secretary Karen Ross. “I would like to thank the farmers and residents of Alameda County who helped us eradicate this infestation by cooperating with the quarantine.”
Alameda County Agricultural Commissioner Cathy Roache: “We’re pleased to report the Medfly quarantine has ended; however, the on-going threat remains. Help us protect our commercial and backyard gardens from future fruit fly infestations. Please, ‘Don’t Pack a Pest’ when traveling, or when mailing or receiving packages.”
The Medfly is known to target more than 250 types of fruits and vegetables, potentially causing severe impacts on California agricultural exports and backyard gardens alike. 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.
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 the state is by “hitchhiking” in fruits and vegetables brought back illegally by travelers as they return from infested regions of the world. Help protect California’s backyard gardens, agricultural, and natural resources; please Don’t Pack a Pest (www.dontpackapest.com) when traveling, or when mailing or receiving packages.
While Alameda County’s Medfly quarantine has ended and there are currently no fruit fly quarantines in California, the ongoing threat of new infestations by non-native species remains. Invasive fruit flies and other invasive species can endanger the state’s agriculture and natural resources, as well as homegrown fruits and vegetables. Agricultural officials are asking residents to help prevent future introductions of invasive species by following these guidelines:
Assist agriculture crews working to protect your garden by allowing them access to your yard to place traps and inspect plants.
When entering California from another state or country, avoid bringing agricultural products – including fruits and vegetables. Help us protect our agriculture, natural resources, and California’s unique biodiversity from invasive fruit flies – please Don’t Pack a Pest (www.dontpackapest.com).
Please do not send or receive any homegrown fruit, vegetables, or meat products, as they may contain invasive species that can “hitchhike” in these products.
Inspect your garden regularly for signs of invasive fruit flies or maggots and report any findings to CDFA at 1-800-491-1899.To learn more about invasive species and how to protect California’s fruits and vegetables, please visit www.cdfa.ca.gov/plant/fruitfly/.
