Medfly bugwood
Florida Division of Plant Industry , Florida Department of Agriculture and Consumer Services, 


The most recent Mediterranean Fruit Fly (Medfly) infestation in San Mateo County was declared eradicated by the California Department of Food and Agriculture (CDFA) as of October 4, 2018. The quarantine began in November of 2017 after routine insect trapping by the Agriculture Department’s pest detection staff discovered two wild-type Medflies within five miles of each other in Half Moon Bay.

With a high reproductive rate, and the ability to breed on more than 250 different fruits and vegetables, the Mediterranean fruit fly is considered the most destructive agricultural pest in the world. To limit the spread of the pest, strict limitations were placed on host material leaving the quarantine area. The quarantine also prompted the mandatory stripping of all fruit from trees near the finds, and strict safeguarding requirements for local farmers’ markets and other sellers of produce within the 56-mile quarantine area.

The prolonged response by state and county employees involved careful trap placement and monitoring for additional flies in the area, and targeted organic-approved pesticide applications near each find site. In addition, almost 200 million sterile flies were released by plane over the twelve square-mile center of the quarantine, to disrupt the mating cycle of any existing medfly populations in the area.

The eradication of the fly and end of the quarantine was a welcome relief to producers, retailers and business owners in the Half Moon Bay area. The most common pathway for exotic fruit flies and other invasive species to enter California is by “hitchhiking” in fruits and vegetables brought back by travelers returning from regions where these pests are common. To learn more about what you can do to prevent the spread of invasive species like the Medfly, please visit

If you have any questions about the Mediterranean Fruit Fly quarantine or San Mateo County’s pest exclusion and detection programs, please feel free to contact the San Mateo County Department of Agriculture/Weights and Measures at (650) 363-4700.