Scientist Expects Medfly Outbreak in a Few Years

No new Medflies have been found in nearly a year since the largest infestation in Southern California’s history, but a UC Davis entomologist says it is only a matter of time before the crop-destroying pests return in full force.

James R. Carey, writing in today’s issue of Science magazine, said an analysis of Mediterranean fruit fly trappings since 1975 indicates that the insect has established itself in parts of Southern California and is spreading through the region.

“The Medfly invasion is much like a cancer,” Carey said. “Its development is latent, insidious, chronic and persistent, which explains why the pest became widespread despite aggressive trapping and seven separate eradication programs.”

Carey, who was a member of the state’s Medfly Science Advisory Panel during the 1989-90 infestation, said Thursday he expected a major outbreak to occur in Southern California in the next few years and predicted a gradual spread of the pest northward along the coast.

“They’re still here,” he said. “If there’s a silver lining, it’s that their spread is a very slow process and we at least have time to prepare.”

Carey’s predictions come during one of the quietest Medfly seasons since the pest was detected in California in 1975.

Not a single Medfly has been found anywhere in the state since the last one was trapped 10 months ago in San Bernardino County.

Along with the lack of observed Medflies, a total of only 16 other fruit flies have been found in the state this year, according to the California Department of Food and Agriculture. None of the discoveries have required aerial malathion spraying.

Gera Curry, a spokeswoman for the department, said the lack of Medfly discoveries supports the state’s claim that the Medfly has been eradicated and is not established in Southern California.

“I’m not surprised at all with the lack of finds,” Curry said. “This just shows (Carey’s) theory is unsubstantiated.”

Even Carey expressed surprise at the lack of finds, although he added: “We’re talking about a long-term pattern. You’d expect some years for them to disappear after extended freezes or an eradication program and then show up again.”

Nevertheless, Carey’s analysis in Science showed that over a period of 15 years the Medfly has often infested the same neighborhoods, suggesting that the insect has never been eradicated. Carey said malathion spraying can reduce the number of Medflies, but a small population survives and continues to breed.

He pointed to the repeated infestations in areas such as Baldwin Park (1981 and 1989), West Covina (1981, 1989 and 1990) and East Los Angeles (1987, 1989 and 1990) as a sign of established populations.

He noted that contrary to the claims of state officials, who believe that Medfly infestations are caused by the illegal entry of infested fruit, airport inspections over a five- to six-year period have turned up only five Medflies, compared to 4,000 interceptions of other fruit flies.

Curry said more recent first-class mail inspections have found Medflies in five packages out of 550 that contained prohibited material.

Fruit Fly Finds

Here is a look at all fruit fly finds in California in 1991. Only 16 fruit flies have been found, none of which were Medflies. None of the discoveries have required aerial spraying. TOTAL FINDS

Mediterranean fruit fly: 0

Oriental fruit fly: 8

Mexican fruit fly: 7

Queensland fruit fly: 1

DATE TYPE CITY COUNTY Aug. 28 Oriental fruit fly Santa Clara Santa Clara Aug. 26 Queensland fruit fly Laguna Beach Orange Aug. 21 Oriental fruit fly San Diego San Diego Aug. 19 Oriental fruit fly Fremont Alameda Aug. 16 Mexican fruit fly Hacienda Heights Los Angeles Aug. 1 Oriental fruit fly Carson Los Angeles July 25 Oriental fruit fly Carson Los Angeles July 23 Oriental fruit fly Upland San Bernardino July 22 Oriental fruit fly Lakeside San Diego July 16 Mexican fruit fly San Diego San Diego July 1 Mexican fruit fly Los Angeles Los Angeles June 26 Mexican fruit fly San Diego San Diego June 7 Oriental fruit fly Alhambra Los Angeles May 2 Mexican fruit fly City Terrace Los Angeles April 18 Mexican fruit fly San Diego San Diego April 11 Mexican fruit fly Chula Vista San Diego

SOURCE: California Department of Food and Agriculture