A Mediterranean fruit fly (Medfly) infestation centered in and around the city of Fremont, California, has been eradicated. The eradication ends a 213-square-mile quarantine that began Sept. 6, 2024.
The California Department of Food and Agriculture (CDFA), the U.S. Department of Agriculture (USDA) and the Alameda County agricultural commissioner’s office accomplished the eradication.
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. Additionally, properties within 200 meters of the detection sites were treated with an organic formulation of spinosad to eliminate any mated females and reduce the density of the population. Spinosad originates from naturally occurring bacteria in soil.
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 Medfly is known to target more than 250 types of fruits and vegetables, potentially causing severe impacts on California agricultural exports and backyard gardens. Damage occurs when the female lays eggs inside the produce. The eggs hatch into maggots and tunnel through the flesh of the produce, making it unfit for consumption.
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. Growers and others have been asked to report any suspected invasive fruit fly sightings to the CDFA, the USDA or their local county agricultural commissioner.
Learn more about invasive species and how to protect California’s fruits and vegetables here.
Source: Citrus Pest & Disease Prevention Program
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