All Clear Given in California Medfly Infestation

The California Department of Food and Agriculture (CDFA), 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 Sept. 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, CA, which prepares sterile flies for release everyday over portions of California.

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.

With this latest eradication, there are currently no fruit fly quarantines in California.

For more information, visit cdfa.ca.gov.