Invasive fruit flies pose a serious threat to California’s farms and backyard gardens, damaging fruits and vegetables in both commercial orchards and home gardens.
In 2023, California experienced one of the worst invasive fruit fly outbreaks that led to quarantines, which prevented residents from sharing homegrown produce for months at a time.
At an August 8 briefing hosted by American Community Media, representatives from the California Department of Food and Agriculture (CDFA) discussed the risks invasive fruit flies and other non-native pests pose to California’s natural vegetation, whether in commercial orchards or home gardens. They also explained why the risk is especially high this year and how collective action can help prevent the spread of invasive pests and protect California’s agriculture by detecting and eradicating pests,
While this year’s fruit fly infestations aren’t as severe, experts say they continue to impact large areas, including a 100-sq mile region in San Diego County.
“They continue to come to California, but between the CDFA, the USDA, and the counties, we continue to eradicate those fruit flies,” said Victoria Hornbaker, Director at the Plant Health and Pest Prevention Services Division, CDFA. The CDFA is collaborating with the U.S. Department of Agriculture (USDA) to control threat levels and has successfully eradicated three quarantined infestations this year.
“So we’re winning,” added Hornbaker.
The Threat
The three most common invasive fruit flies in California are the Mediterranean, Mexican, and Oriental fruit flies. Because these flies are not native to California, said Hornbaker, they have no natural predators to keep their populations under control. As a result, they can spread quickly and cause serious, potentially irreversible damage to farms and home gardens.
“These flies lay their eggs inside the fruits and vegetables where the growing larvae or maggots feed, and they ruin the produce from the inside out,“ she explained. “While the produce may still look good on the outside, these maggots feed and destroy the flesh of the fruit.”
Invasive fruit flies can pose a threat to over 400 types of specialty crops grown in California, said Hornbaker, costing the United States approximately $40 billion each year in damages.
They can also damage over 250 types of fruits and vegetables, but their impact goes beyond losing crops. They could lead to higher food prices, less access to fresh produce, and financial losses for farmers and ranchers, which affect the health and well-being of Californians.
Entry and Early Detection
According to CDFA, fruit fly invasions have been detected in urban and suburban areas, where invasive pests enter California through several high-risk pathways; state authorities are taking steps to prevent the pests from spreading.
One of the most probable ways that pests enter is when travelers bring fruits and vegetables from other states and abroad
At airports, Customs and Border Protection (CBP) teams control the entry of fruit flies or infested produce via air, using trained beagles and canines to sniff out fruits, vegetables, and plant materials at entry checkpoints. CBP also checks passengers traveling by land at international border stations with Mexico. Despite the effectiveness of these checks, some items that harbor pests still slip through, especially souvenirs made from natural materials, “such as wooden handicrafts.” Hornbaker urged travelers not to bring back produce or plant-based items into California.
Pests could evade safety checks and risk-mitigation protocols when consumers purchase produce through online marketplaces or unverified sources, said Huong Dang, an Orange County resident and an Administrative Support Specialist at the Orange County Agricultural Commissioner’s Office.
For example, “A high interest in exotic fruit trees and vegetables, especially from Vietnamese garden groups in the U.S.,” leads fellow Vietnamese residents to Facebook marketplaces or Etsy when they cannot source these fruits locally.
Sometimes these online offers scammed purchasers by sending different products or nothing at all, explained Huong. He assisted agricultural inspectors in identifying non-native plants, many of which are unsuitable for growing conditions in Orange County,
Huong recommends that gardening enthusiasts buy only from verified sources or local nurseries who know “which plants are conducive to local climatic and soil conditions,” and which plants are disease-free.
A third pathway to entry is shipments of fruits and vegetables that unintentionally harbor invasive pests, sent by out-of-state friends and family, and even people hitchhiking with agricultural products. ”It’s the vitality of the state’s crops…that is at risk,” said Hornbaker. Produce that enters California through commercial trade with other states or internationally undergoes measures to prevent infestations and the spread of invasive pests, she added. Buying from local, certified markets could significantly prevent invasive fruit flies from destroying California’s rich and diverse crops.
Detection, Exclusion, Eradication
Currently, 16 border protection stations established by CDFA in Oregon, Nevada, and Arizona, which share borders with California, implement pest exclusion practices using canine teams and county and state inspectors to examine shipments of plants, fruits, and vegetables.
CDFA has set up more than 100,000 traps across the state to monitor invasive pests through trapping and visual inspections. The agency’s response depends on how widely the pests have spread, explained Abraham Lopez-Zuniga, Emergency Response Team Lead at CDFA.
For example, when a single fruit fly is detected and it is not a mated female, CDFA responds by setting additional traps and conducting visual surveys to monitor whether more pests are present.
If pest inspectors detect an infestation (multiple flies) they decide whether to trigger eradication efforts; the next response, depending on weather conditions, is a quarantine that could last through many life cycles of a fruit fly,
As part of the response, trained inspectors go door to door in affected areas to look for signs that flies are laying eggs. They examine fruit for puncture marks or rotting, which can indicate that a fly has laid eggs and larvae are present. The presence of larvae confirms that the flies are reproducing and leads to further action.
Treatment may include spraying the base of plants and trees with insecticidal dust to slow reproduction and eventually eliminate the flies. Another measure requires removing all fruit from the area where female flies were found to prevent the spread and break the flies’ life cycle.
In LA an early warning system helps CDFA detect invasive pests before they reproduce and spread.. “We have 75 inspectors who work year-round placing and checking traps that are designed specifically to attract invasive fruit flies and other agricultural pests,” said Jordan Petersen, Deputy Agricultural Commissioner/Sealer, Los Angeles.
Screening procedures include using trained canines to detect packages of agricultural produce at International ports and entry points.
Agricultural inspectors also check facilities like FedEx, UPS, and U.S. Post Offices to determine the source of packages, the likelihood of infestation, and clearance of legal entry into California.
The CDFA had devised a comprehensive and relatively successful response to address a major challenge – the volume of packages, estimated at over 8 million a day entering California, explained Petersen.
Six detector dog teams screen large volumes of packages quickly, while licensed agricultural inspectors determine whether such items are suitable for entry into California.
However, the control and elimination of invasive pests needed the cooperation of residents, home gardeners,, and communities, said the experts..
It Takes Collective Action
CDFA consistently works on spreading awareness and educating California residents with the following advisories for responsible. travel
Travel Tips: Don’t Pack a Pest
- Don’t bring fresh fruits or vegetables, plants, or other natural materials into California from other states or countries. Declare agricultural items when entering California.
- Clean outdoor gear, boots,, and vehicles before travel and when returning to California.
- Learn more at StopInvasivePests.com and DontPackaPest.com
Shipping and Receiving Tips:
- Don’t buy homegrown produce online.
- Don’t ship homegrown produce or other natural materials into California from other states or countries.
- Buy produce from local, licensed retailers and nurseries. Here is a list of CDFA-approved nurseries.
- Learn more at StopInvasivePests.com.
CDFA also recommends the following :
- Regularly inspect home gardens and report any signs of invasive fruit flies or maggots to CDFA’s Pest Hotline at 1-800-491-1899.
- Support agricultural officials working in your neighborhood.
- Follow quarantine guidelines if you’re in an impacted area.
- Visit CAFruitFly.com for a list of active invasive fruit fly quarantines in California.
- Dispose of fruits and vegetables in quarantined areas in double plastic bags in the regular trash. Don’t put them with green waste.
