(Case study: The Mediterranean Fruit Fly in Alameda County, Sept. 2024)

Mediterranean fruit fly is considered to be the most destructive agricultural pest in the world. (Photo by 5193024-Medfly, Florida Division of Plant Industry, Florida Department of Agriculture and Consumer Services, Bugwood.org)

 Invasive Species are either here or on their way.

Invasive species threaten California's home gardens and more importantly California's agriculture, ecology and environments.  Invasive species are non-native (or exotic) species whose introduction is likely to cause economic or environmental harm, or harm to human health. There are infestations that require an immediate and rapid response to eradicate the pest before it can become established. The discovery of the one wild mated female Mediterranean fruit fly in Alameda County prompted such a response, showing the high priority of eradicating what is considered to be the world's most destructive agricultural pest before it can establish itself in California.

Some other invasives are already established in California, and some we are on the watch for, knowing there is a high likelihood of them being detected in California. Some are present in Southern California and we are on alert for them making their way to our counties here in Northern California.

This blog series focuses on a few invasives, mostly plants and insects, but there are also invasive fish, mammals and birds. The invasive exotic (non-native) fruit flies – Caribbean, Guava, Mediterranean, Melon, Mexican, Olive, Oriental, Peach and others – are all serious threats to home gardeners and the agricultural economy.  Asian Citrus Psyllid and Huanglongbing Disease, Invasive Shothole Borers, Tree-of Heaven, Brown Marmorated Stinkbug, European Grapevine Moth, and Spotted Lanternfly are just some of the invasives that California is monitoring for their appearance or spread in California.

Invasive Plants and Pests: Major Threats to California's Agriculture, Home Gardens and Environments

Olive fruit fly poses a severe economic threat for the state’s commercial olive growers. (Photo by 5430505 olive fruit fly, Lorraine Graney, Bartlett Tree Experts, Bugwood.org)

In some cases, non-native plants and pests become serious pests, while others blend in and do not cause noticeable problems. California is on the lookout for non-native invasive species that result in economic costs in order to:

• control invasives
• reduce rate of spread
• inspect agricultural products to prevent accidentally moving invasives to new areas.

In addition, financial costs to farmers to control pests, often with pesticides, results in higher food prices for the consumer. The economic threat can be to agriculture generally or to growers of specific crops such as grapes or citrus. 

There are also additional risks to the environment:

• Upset to the ecosystem, crowding out native plants and animals
• Greater chance of wildfires, with greater intensity
• Depletion of the water table
• Invasive plants can be preferred hosts for invasive pests (These non-native plants provide food and shelter particularly suitable for invasive pests, promoting uncontrolled population growth. The California environment lacks the predators from their native habitat that would normally keep the pest population manageable.)
• There are costs to ornamental trees dying because of pests and then needing to be removed

In California, at least $3 billion is spent annually on eradicating invasive pests, according to the University of California at Riverside.

How Invasives Arrive and Become Established

Invasive species are spread by human activity, often unintentionally. Now, with the ease of travel nationally and internationally, there is greater potential for exotic or non-native species to arrive unnoticed. Rapid transportation makes it likely that accidental hitchhikers survive long distance travel. Ornamental plants, along with hitchhiking insects, can become invasive after escaping into the wild. Insects can be unintentionally transported and spread to new areas when they or their eggs are on things, such as plants, plant material, vehicles, wood, that are moved. The diversity of climates and habitats in California can result in the right combination for exotic organisms to become established.

Invasive Plants Originating from the Nursery Industry

Tree-of-heaven, an invasive, was once a popular ornamental tree commonly found in nurseries. (Photo by 5541618 tree-of-heaven, Richard Gardner, Bugwood.org)

The California Invasive Plant Council (Cal_IPC) has a list of non-native invasive plants that either have already impacted natural areas or are at high risk of becoming invasive, damaging wildlife habitat, degrading food and water supply and more.  Many of these plants were intentionally introduced by the nursery industry as ornamental landscape species. According to the UC IPM Pest Note on Invasive Plants, about 60% of the species listed were intentionally introduced, and most of that 60% came through the nursery industry as ornamental landscape species.

Management of Invasives

The Mediterranean fruit fly (the medfly) is an example of how invasives can be managed. In September 2024, one mated female was found in Alameda County. This fly is known to target over 250 fruits and vegetables. The fly causes damage when females lay eggs in the produce.  The eggs hatch into maggots that burrow through the produce making it unfit for sale or consumption. The Medfly is considered to be highly invasive but is not yet established in California. It has the potential to have a devastating effect on agriculture and home gardens,so there will be a concerted, coordinated plan to eliminate the Medfly.

Proactive Management - Quarantines, Inspection, Bans on Imports or Sales

Management of invasive species may be proactive, focusing on the exclusion of the pest. Exclusion management uses quarantine laws, the inspection of imports for hitch-hikers, and the banning of import or sale of certain plant and animal species.  If detected at a very early stage of invasion, the goal will be to eradicate the pest, as it is currently being done with the fruit flies, including the Mediterranean fruit fly pictured below.

Mediterranean fruit fly causes quarantine in Alameda County, September, 2024 (Photo by 1317084 Mediterranean fruit fly, USDA ARS Photo Unit, USDA Agricultural Research Service, Bugwood.org)

The Mediterranean fruit fly  - Proactive Management in Action

The September 2024 discovery of a single mated female Mediterranean fruit fly in Fremont resulted in a quarantine of 71 square miles in southern Alameda County, now expanded to 83 square miles. The California Department of Food Agriculture (CDFA) announced the quarantine, the first in Alameda County since 1981. View the quarantine map. The quarantine affects growers, wholesalers and retailers of susceptible fruit, as well as local residents.

An invasive fruit fly quarantine , what does it mean for home gardeners?

• Check to see whether you are in the quarantine area
• Home gardeners are encouraged to consume their own fruits and vegetables, and not move produce from their properties.
• Do not compost your fruits and vegetables.
• When disposing of produce, double-bag the waste and put it into the trash instead of the green waste bin.
• Don't let ripe produce fall to the ground.
• Inspect your garden for signs of invasive fruit flies or maggots.
• If you think your fruits and vegetables may be infected with fruit fly larvae, call CDFA's Pest Hotline (800) 491-1899 or reportapest@cdfa.ca.gov

How else can Californians help with the Medfly?

• The majority of fruit flies and other invasives are found in urban and suburban communities.  The most common pathway for these invasive species to enter our state is by “hitchhiking” in fruits and vegetables brought back illegally by travelers as they return from infested regions of the world.
• To help protect California's agriculture and natural resources, CDFA urges travelers to follow the Don't Pack a Pest program guidelines (https://www.dontpackapest.com/)
• Buy fruit trees and vegetable plants from licensed California nurseries.

What else is being done to eradicate the Medfly?

In the case of the Mediterranean fruit fly, the plan to eliminate the pest uses the standard Medfly program by the CDFA and is the safest, most effective, and most efficient response program available. Sterile male fruit flies will be released in a 39-square-mile area around the infestation at a rate of 250,000 male fruit flies per square mile per week. The sterile males mate with the female fruit flies but do not produce offspring. The goal is to leave no new fruit flies to replace the wild ones as they reach the end of their short lives.

In addition, an organic form of Spinosad is being used to treat properties within 200 meters of the detection site to reduce the population of fruit flies. Fruit removal will take place on properties within 100 meters of those with mated females, larval detections and multiple adult detections.

Reactive Management - Do Nothing, Cultural, Chemical, Biological Controls; or Integrated Pest Management (IPM)

Another approach is reactive management where exclusion and eradication is impossible. This is used when an invasive species has successfully invaded and high populations are now spread over large areas.

Options include:

• do nothing, where there is no management plan in effect, as is often done with invasive weeds in national, state or county parks
• use cultural controls, such as crop rotation, use of plants resistant to specific plant disease, or mulching to promote growth of beneficial organisms
• use chemical controls (pesticides), which are often expensive, need repeated applications, and they may leave pesticide residues leading to human safety concerns
• use biological controls, which involve the use of natural enemies (predators, parasitoids and pathogens) of the invasive species
• use integrated pest management which combines a variety of control strategies to control an invasive pest.

    
The Big Three Protecting California's Food Supply with Information, Detection, and more …

Mexican fruit fly infests many fruits and vegetables, particularly citrus and mango (Photo by 2089 Mexican fruit fly laying eggs, Jack Dykinga, USDA AGricultural Research Service, Bugwood.org)

The US Department of Agriculture, the California Department of Food and Agriculture and the Agricultural Commissioners of each California county work together. They have services that gather and provide information on invasives, provide detection services and coordinate management of invasives.

1)  U.S. Department of Agriculture

National Invasive Species Information Center (NISIC) was established in 2005 at the U.S. Department of Agriculture (USDA's) National Agricultural Library (NAL) to meet the information needs of users, including the  National Invasive Species Council (Council or NISC).

The NISC provides "the high-level vision and leadership necessary to sustain and expand Federal efforts to safeguard interests of the United States by preventing, eradicating, and controlling invasive species, as well as restoring ecosystems and other assets impacted by invasive species."

invasivespeciesInfo.gov  is managed by NISIC at NAL. This site serves as a gateway to invasive species information, including federal, state, local and international sources.  It provides selected U.S. and International resources from agencies and organizations with an interest in the prevention, control, or eradication of invasive species, organized by geography.

2)  California Department of Food and Agriculture

CDFA Plant Health and Pest Prevention - Border protection, Pests Detection and Exclusion, Quarantine Information and more

The California Department of Food and Agriculture (CDFA) has Plant Health and Pest Prevention Services to protect California's food supply from exotic pests. https://www.cdfa.ca.gov/plant/ 

CDFA early detection and eradication projects

It also has pest detection/emergency projects for the early detection and prompt eradication of serious agricultural pests from California.  https://www.cdfa.ca.gov/plant/PDEP/

CDFA list of invasives

There is a list of insect pests and plant diseases targeted by the CDFA detection and emergency projects. The list includes Asian Citrus Psyllid and plant disease Huanglongbing (HLB), invasive fruit flies,  Spotted Lanternfly 

https://www.cdfa.ca.gov/plant/PDEP/target_pests.html

3)  The Alameda County Department of Agriculture/Weights and Measures  (Agricultural Commissioner of Alameda County)

Agricultural Commissioner of each county is charged with the protection of California agriculture, the protection of the environment as well as protection of the public's health and safety. Nearly all of California's counties have combined the offices of the Agricultural Commissioner with the County Sealer of Weights and Measures. In Alameda County, that office is the Alameda County Department of Agriculture/ Weights and Measures.

The Alameda County Department of Agriculture / Weights and Measures is an essential part of the defense for California agriculture and the environment against the invasion of exotic pests. Its programs include pest exclusion and pest detection.

What Can Californians and the Home Gardener Do?

Innocent sharing or movement of infected plants or other materials can have long-term effects costly to all Californians.  Here are some suggestions from UC Riverside Center for Invasive Species Research for how you can help.

• Select garden plants that are not likely to be invasive. Check with local garden center or online with https://plantright.org/about-invasive-plants/better-plants/  Buy locally from a reputable source.
• Do NOT move soil and firewood from one area to another.  Often soil and firewood contain hitchhiking species of insects, bacteria, fungi or worms.
• Do not release pets, aquatic animals or plants into the wild.
• Wash and clean outdoor gear, boats, and vehicles before returning home to reduce the likelihood of unwanted hitchhikers moving into new areas.
• Be supportive of the inspections, quarantines, bans on sales or imports and other actions of the CDFA.
• Be supportive of the pest detection efforts of the Alameda County Department of Agriculture (Agriculture Commissioner's office) by allowing insect survey traps on your property.
• Keep a Lookout. Learn more about the invasive pests and diseases and be on the watch for pests that have a high likelihood of moving into California or spreading into new areas within California.
  • https://ipm.ucanr.edu/invasive-and-exotic-pests/
  • https://www.iscc.ca.gov/publications/ISCC_trifold_LR.pdf
• Report Sightings. Be a “citizen scientist”.  Call California's Pest Hotline (800) 491-1899 or contact your local Agricultural commissioner. (510) 670-5232

Resources:

Alameda County Department of Agriculture / Weights and Measures
(Agricultural Commissioner of Alameda County)
Pest Exclusion https://www.acgov.org/cda/awm/agprograms/pestexclusion/index.htm
Pest Detection https://www.acgov.org/cda/awm/agprograms/pestdetection/index.htm

California Department of Food and Agriculture https://www.cdfa.ca.gov/invasives/

California Invasive Plants Council (Cal IPC) invasive plant species that impact natural areas https://www.cal-ipc.org/plants/      These plants damage wildlife habitat, agricultural production and water resources.

2024 California Invasive Species Action Week Lunchtime Talks https://ucanr.edu/sites/invasivelunch/2024/

National Invasive Species Information Center US Department of Agriculture https://www.invasivespeciesinfo.gov/

Invasive Plants Pestnote https://ipm.ucanr.edu/PMG/PESTNOTES/pn74139.html

UC Riverside Center for Invasive Species Research  https://cisr.ucr.edu/invasive-species
https://cisr.ucr.edu/resources/invasive-species-faqs#how-can-invasive-species-be-ma

What are Exotic and Invasive Pests
https://ipm.ucanr.edu/invasive-and-exotic-pests/What-are-exotic-and-invasive-pests/

Have a gardening question? We'll help. You can reach us by:

• Emailing acmg@ucanr.edu. Please include a photo of the problem, if you can, plus your name, phone number, city and a description of the problem.
• Using our online form.
• By phone, during our office hours, 10 am to noon Wednesday and 11 am to 1 pm Thursday: 510-670-5645. At other times, please leave a message and we'll return your call during our office hours.
• In person at our Hayward office, during our office hours, only by appointment.