Celebrating Three Decades of CDFA’s Medfly Preventive Release Program
This year marks the 30th anniversary of California’s Mediterranean fruit fly (Medfly) Preventive Release Program (PRP), a landmark pest prevention effort that helps protect agriculture, natural resources and urban food production in the Los Angeles Basin and across the state from devastating environmental and economic losses.
Established in 1996, the Medfly PRP was created in response to the increasing threat of Medfly introductions into the Los Angeles Basin, driven by growing international trade and travel. Prior to the program’s creation, California relied largely on reactive eradication efforts to address repeated introductions of the destructive pest that threatens more than 250 types of fruits and vegetables. The PRP represented a shift toward a proactive, science-based prevention strategy, proving more cost-effective while reducing pesticide use.
The PRP utilizes sterile insect technique (SIT), an environmentally friendly pest management approach that functions as a form of biological ‘birth control.’ Sterile male Medflies are released year-round at a weekly rate of 62,500 to 125,000 flies per square mile throughout portions of Los Angeles, Orange, Riverside and San Bernardino counties, covering approximately 1,750 square miles. The sterile males mate with wild females, resulting in no viable offspring and preventing populations from becoming established, while an extensive trapping network monitors for wild Medfly introductions. Entomologists identify any trapped insects, and program specialists continuously analyze data to assess effectiveness and guide operations.
Results to date have been significant. Before the PRP was established, California averaged approximately 7.5 Medfly infestations annually. Since preventive releases began, infestations have declined by more than 90%, averaging fewer than one infestation per year.
Additionally, the strategic location and infrastructure of the Medfly PRP facility in Los Alamitos can be mobilized quickly to respond to Medfly detections anywhere in the state. Most recently, the facility coordinated releases to address a Medfly infestation in Santa Clara County, which was successfully eradicated, resulting in the lifting of a 241-square-mile quarantine around San Jose.
The program protects California’s $18.5 billion agricultural economy while helping preserve residents’ ability to grow fresh fruits and vegetables at home, and with Southern California being a critical hub for agricultural trade and distribution, program impacts extend even beyond county and state lines.
Earlier this year, the California Department of Pesticide Regulation (DPR) honored the Medfly PRP with its 2025 Integrated Pest Management Achievement Award, recognizing the program’s long-term effectiveness and environmentally responsible approach to pest prevention. The award is presented as part of DPR’s annual recognition of outstanding programs and organizations across the state that focus on using safe, effective and sustainable pest management practices.
This 30-year milestone also coincides with the 50th anniversary of USDA Animal and Plant Health Inspection Service’s Medfly Program. Established in 1975 through a partnership with Mexico and Guatemala, the program was designed to prevent the northward spread of a pest capable of infesting more than 250 varieties of fruits and vegetables — and has become an international model for protecting agriculture through science, innovation and cooperation. Today, the program rears approximately 1.2 billion sterile Medflies each week at the El Pino facility in Guatemala, providing a critical line of defense for agricultural production and trade throughout North America.