Medfly Infestation in Dixon 'One of Many Isolated Pockets of Medfly Infestations in California,' UC Davis Entomologist Says

Sept. 19, 2007 (More photos)
(Update, as of Oct. 30, 2007: Thirteen medflies--3 unmated females and 10 wild males--were trapped, live, between Sept 10 and Sept 17 in downtown Dixon.  Larvae found: 33 at one downtown Dixon site on Sept. 13, and 29 at another downtown Dixon site on Sept. 19 for a total of 62 larvae. Source: Solano County Agricultural Commissioner Jerry Howard)

"The medfly has been captured in 160 cities in the state. There are 478 cites in California, so medflies have at one time (or are now) present in one of every three cities in the state." --James Carey

How and when did the medfly arrive in California? See James Carey's theory

The Mediterranean fruit fly (Ceratitis capitata). Click for high resolution. (Photo by Jack Kelly Clark, UC Division of Agriculture and Natural Resources) DAVIS— The Mediterranean fruit fly infestation detected in the northern Solano County city of Dixon in mid-September may be just one of many isolated pockets of medfly infestations in California, says noted University of California, Davis medfly expert James Carey. “This is really serious because the invasion process is so insidious,” said Carey, a UC Davis professor of entomology who has published widely on what is considered the world’s worst agricultural insect pest. Carey suspects that the medfly has been multiplying and spreading undetected--like cancer--for years.  “It’s may be a symptom of a much larger problem. But any way you look at it, this is the first really big outbreak in the Central Valley.” “We’ve never really caught them in the Central Valley before and here they are,” Carey said.  “They didn’t just fall out of the heavens. We should look at this as a chronic, cancer-like process rather than a flu-like event.” The initial find of four medflies on Monday, Sept. 10 in a single trap at the intersection of C and Washington streets marked the first-ever discovery in Solano County and the second in the 400-mile Central Valley. James Carey Frank Zalom Within a five-day period, from Sept. 10-14, ag officials detected 12 adults at five sites, and 33 larvae infesting a single peach tree in a backyard, all within the Dixon city limits. “It’s definitely breeding, but it’s all within the city so far,” said Kevin Hoffman, primary state entomologist with the California Department of Food and Agriculture (CDFA). A 114-mile radius quarantine took effect on Tuesday, Sept. 17 and is expected to last nine months to a year. The only medfly captured in the Central Valley, Carey said, occurred at the peak of the Bay Area medfly outbreak in 1982 in the city of Stockton, San Joaquin County. With Dixon, that makes 160 cities in California with medfly captures, Carey said.  “It’s like a puzzle,” Carey said. “You find one here and over there and you need to consider the possibility that they’re all connected and not isolated outbreaks. For example, the olive fruit fly was first discovered in 1998 in California but within a few years was found up and down the state. How did it get statewide status within a few years? It’s because it’s been here for a long time.”  “I wouldn’t be totally shocked, if at some point, the medfly is found in multiple regions of California,” Carey said. ”Just as most of cancerous growth occurs at subdetection levels, we may be dealing with  scores of medfly pockets scattered around the state, all of which are at subdetection levels.” DNA testing on the first five medflies revealed they are of the BBBB strain, commonly found in Hawaii and Venezuela, said state plant health director Helene Wright of the Animal and Plant Health Inspection Service (APHIS), USDA. Wright said this is the third occurrence of BBBB strain detected in California: a single medfly in Santa Ana in 1993; and medflies in La Jolla in 1998. Hawaii and Venezuela have only the BBBB strain, but it is also commonly found in Africa, South America, Madeira and the Azores, she said. “We are trying to track the potential pathways.” Carey said the key pathway is apparently not by air travelers. His research published in 1991 in Science magazine indicated that USAD/APHIS in Honolulu found only “two to three medflies in five years or so despite 100 percent screening of bags and carry-ons.” (See publications below) Carey said it “is way too early in this outbreak and too few points yet to start connecting too many dots. However, to me there is something going on statewide with the medfly as well as several other species. Note that both apple maggot fly and olive fly are established in state and 10 years ago neither were even detected (or only in isolated spots in low numbers). Nowhere in the United States or in the world are there medfly outbreaks like in California. Not Texas, not Florida, not any of the southern coastal states or the Southwest. They all are suitable for medfly establishment and collectively have huge urban populations with many immigrants, travelers and so forth. So something different is going on in our state.”  “I wouldn’t be totally shocked, if at some point, the medfly is found in multiple regions of  California. Just as most of cancerous growth occurs at subdetection levels, we may be dealing with  scores of medfly pockets scattered around the state, all of which are at subdetection levels.” —James Carey “Although I certainly wouldn’t connect the dot at Dixon with the dot in San Diego right now, it is conceivable to me that there are medfly metastases in many different places that are hanging on by a thread that were introduced many decades ago. Let’s see how this outbreak plays itself out. Probably cool weather will cut this outbreak short. However, over the next several years trapping in region of Sacramento Valley will provide information on whether this outbreak is restricted to Dixon area or whether more far reaching. The 114-mile radius quarantine will wreak economic havoc on growers, shippers and processors of fruits, vegetables and nuts, and in turn, will adversely affect consumers. Dixon is in the throes of tomato and walnut harvesting. The owner of a 65-acre organic produce farm that ships to 800 clients said he may lose $10,000 a week in potential sales. The pest, smaller than a house fly, is considered one of the world’s worst agricultural insect pests due to its wide distribution, wide range of hosts (its larvae infest more than 260 fruits and vegetables) and its ability to tolerate cool climates. Solano County Agricultural Commissioner Jerry Howard described the medfly: as “the single biggest threat to agriculture there is, and we are taking this very seriously.” Since the initial find on Monday, Sept. 10, the CDFA Medfly Action Plan kicked into high gear, Hoffman said. Since then, ag officials have: Stripped all fruit from trees within a 100-meter radius of all medfly finds Ground-sprayed the organic compound Naturalyte (the active ingredient is Spinosad, a naturally occurring product of a soil bacteria) within a 200-meter radius of all medfly finds Set 1,700 fruit fly traps within an 81-square mile grid  in all of Dixon and the surrounding area from near the Yolo County border to Midway Road Began aerially releasing 1.5 million sterile male medflies (dyed pink for easy detection) over a 12-square mile area on Sept. 14, with weekly releases of 3 million medflies scheduled for at least nine months Set up a command center, with four portable buildings and a task force of 25 on the Dixon May Fair grounds for what is expected to be a one-year stay Established a 114-square mile quarantine zone of fruits, vegetables and nuts in the area CDFA agricultural pest control specialist Ian Walters answers questions at the Sept. 14 press conference at the Nut Tree Airport. He is holding a container of sterile male medflies, dyed pink for easy detection. (Photo by Kathy Keatley Garvey) The CDFA protocol is “like a cookbook,” Hoffman said.  “We know what to do and what’s going to happen.” “CDFA is doing exactly the right thing,” Carey said. “You’ve got to react immediately, of course. But once things are under control, they need to thoughtfully consider the nature of invasion so they make sure they are treating the disease and not just the  symptoms. With an invasion, some people view it as a flu; I view it as a cancer.” CDFA’s quick emergency response follows standard procedures that have served “them well in the past,” said UC Davis entomologist Frank Zalom, a member of Pete Wilson’s Exotic Pest Eradication Task Force in 1995, triggered by the extensive medfly outbreak in the Los Angeles area. “One of the things we really worry about is that it has so many crop hosts and the  impact of potential quarantines on different crops,” said Zalom, who studied the overwintering capabilities of medflies in Barcelona, Spain while on a Fulbright fellowship in 1992-93. Earlier medfly infestations in California—the seven-county Bay Area infestation in 1980 and the 1989-90 and 1993-94 infestations in southern California —involved the aerial spraying of the controversial pesticide malathion.  “The spraying of the spinosad bait is a safe approach,” Zalom said.  “It has been used successfully by our growers to treat olive fruit flies, and it has been used successfully in Hawaii to suppress there.” Zalom, an integrated pest management specialist, said he wouldn’t be at all surprised if his olive fruit fly traps used for his research on the UC Davis campus, about 6 miles from Dixon, yield “pink” medflies. The right wind could waft the medflies to outlying areas, he said.  The pest, first detected in California in 1975, prefers such thin-skinned hosts as peach, nectarine, apricot, avocado, grapefruit, orange, and cherry. The pest’s permanent presence in California could result in estimated annual losses of $1.3 to $1.8 billion, according to CDFA Secretary A.G. Kawamura. Carey, a former member of the CDFA’s scientific advisory panel, said the aerial release of sterile male medflies—3 million a week until June 2008—“could make it difficult to monitor for wild flies in the release zone because of trap overload of sterile flies.” The medflies are reared  in the CDFA/USDA facility at Los Alamitos as part of the Preventive Release Program, an ongoing program which prepares hundreds of millions of sterile flies weekly for release over the Los Angeles basin and other high risk areas. Launched in 1996, the release has dramatically reduced the number of infestations, said Steve Lyle, director of the CDFA’s Office of Public Affairs.  Between 1987 and 1994, the state recorded an average of 7.5 medfly infestations each year in California. Since the inception of the Preventive Release Program, the tally is just five infestations statewide, Lyle said. The sterile male flies “have a proven track record in southern California of breeding with wild females to help achieve eradication,” Lyle said. “The females breed once and if they breed with a sterile male that ends their reproductive activities.” The female medfly may lay one to 10 eggs per fruit or as many as 22 eggs per day. She may lay up to 800 eggs during her lifetime, but usually about 300.  “We have found medflies in the residential areas of Dixon, and we want to keep them from infesting the commercial crops,” Solano County Ag Commissioner Howard said. Agricultural crops being harvested are tomatoes, apples, peaches and walnuts, he said. Pending are persimmons, pomegranates and wine grapes. The adult medfly, averaging 3.5-5.0 mm in length, has a predominantly dark body with two white bands on the yellowish abdomen. The wings have brown, yellow, black, and white markings. The larvae, creamy white, may reach 0.4 inches in length within the host fruit. For more information about the Mediterranean fruit fly or to report discoveries of suspected infested fruit, call the CDFA toll free pest hotline: (800) 491-1899 or access the CDFA Web site. Map of the Central Valley, courtesy of Wikipedia Central Valley, California The Central Valley, a 400-mile agricultural region stretching from the San Joaquin Valley to the Sacramento Valley, or from Kern County to Shasta County, is drained by the Sacramento and San Joaquin rivers and bordered by the Cascade Range to the north, the Sierra Nevada to the east, the Tehachapi Mountains to the south, and the Coast Ranges and San Francisco Bay to the West. Its population is approximately 6.5 million. Counties in the Central Valley are: North Sacramento Valley (Shasta, Tehama, Glenn, Butte, Colusa) Sacramento Metro (Sacramento, El Dorado, Sutter, Yuba, Yolo, Placer) North San Joaquin (San Joaquin, Stanislaus, Merced) South San Joaquin (Madera, Fresno, Kings, Tulare, Kern) (Source: Wikipedia) Publications: Carey JR (1991). Establishment of the Mediterranean fruit fly in California. Science. 253, 1369-1373. Link to PDF. Carey JR (1996). The future of the Mediterranean fruit fly population in California: a predictive framework. Biological Conservation. 78, 35-50. Link to PDF. More Carey medfly publications Molecular research by separate investigators on medfly infestations in California Excel chart of California cities and medfly captures (James Carey) California Agricultural Commissioners (CDFA) Back to News -Kathy Keatley Garvey Communications Department of Entomology (530) 754-6894