Authorities issued a quarantine on Aug. 21, 2025 for a section of Santa Clara County after Mediterranean fruit flies, or Medflies, were found in the city of San José, according to the California Department of Food and Agriculture.
The CDFA announced the quarantine after two wild female Medflies were detected in the area. As an invasive species, Medflies are a significant threat to California agriculture.
Medflies can infest over 250 varieties of fruit and vegetables. If left unchecked, the invasive pest could quickly spread and damage home gardens and major agriculture producers alike.
The quarantine is still in effect and covers about 109 square miles, mostly around the city of San José, but also affects parts of Santa Clara, Campbell, and Los Gatos. Residents in the quarantined area are being asked not to move homegrown fruits and vegetables off of their property, which could spread the fly to other areas.
Medflies harm agricultural produce by laying its eggs inside fruit. When the larvae hatch, they dig tunnels through fruit, rendering it inedible. Though humans are in no danger from the fly or consuming infested fruit, their damage to agricultural output can be devastating.
California is the country’s leading agricultural producer, creating a considerable portion of the fruits and vegetables eaten in the United States.
“Medflies damaging foods and crops makes buying produce more expensive with the use of pesticides, which also raises questions and concerns of environmental and health impact,” said Edison Lew ’26.
To eradicate the infestation, CDFA has launched a joint operation with the United States Department of Agriculture and the Santa Clara County Division of Agriculture. Authorities have begun releasing sterile male Medflies into the area, a strategy that has been in use in California since 1996.
Because male Medflies only mate once in their lifetime, no offspring are produced when sterile males mate with wild females, thus decreasing the population.
In addition, properties within 200 meters from where the flies were detected are being treated with an organic pesticide derived from a naturally occurring soil bacteria, called Spinosad. Some produce and host plants within 100 meters of detection sites may also be taken down to eliminate any eggs and larvae.
Local residents may also see the impact of the quarantine in their daily life. Home gardeners are encouraged to eat produce on their property, responsibly dispose of fruit that isn’t eaten, and allow agricultural crews to check plant material and set traps.
While it might not be a statewide concern right now, Medfly infestations are a consistent occurrence in California, and there have been a few situations where the true potential of Medflies was seen.
In 1989, a planned attack by “biological terrorists” left the Department of Agriculture spending $60–$120 million to eradicate 12 infestations around the Los Angeles area.
Highlighting the potential devastation from these little insects, biology teacher Colleen O’Rourke warned, “The Mediterranean fruitfly (Medfly) represents a severe risk to the economics of California and the U.S. in general.”
“The fly larvae attack fruit crops, destroying the fruit itself and ruining it for sale. Since California’s economy is still heavily dependent on agriculture, this could be devastating.”
San Francisco residents might not be completely unaffected, with a potential for some food sources being compromised by the Medfly.
“The government should take protective measures to limit invasive species,” suggested San Francisco Sunset resident Timothy Yuen ’26. “They should protect farmers. They could try releasing more native predators to control the Medfly population.”
