Medfly Scientist Adds Fuel to Debate : Infestation: State adviser says the pest was never eradicated from Northern California as previously believed.

James R. Carey, the entomologist who contends that the Mediterranean fruit fly has been entrenched in Southern California since the mid-1970s, says his research also indicates the pest has resided in Northern California for nearly as long.

Carey, one of five scientists advising the state in its campaign to eradicate the Medfly from Southern California, said in an interview that the pest very likely was never eradicated from Northern California in the early 1980s, despite a massive pesticide program.

His thesis is that the state’s system of trapping has failed to accurately chart the Medfly population, luring officials into the belief that they have successfully rooted out sporadic infestations.

Other scientists and agricultural officials, although conceding the system of Medfly trapping is porous, nonetheless challenge Carey’s conclusion--and, most important, its logical extension that aerial pesticide spraying has been a failure.

Carey bases his new claim on the reappearance of the Medfly last year in Mountain View, a community south of San Francisco. The fly was trapped within a few miles and, in some cases, just blocks from where it was found during the 1,300-square-mile Northern California infestation in 1980-82.

The proximity of the discoveries, Carey believes, indicates these are not random infestations caused by travelers or immigrants bringing in infested fruit but rather the re-emergence of simmering fly populations.

Although the pattern of repeated infestations is more apparent in Southern California, he said the Northern California infestation provides one more provocative piece of evidence that the state has never completely eradicated the pest and may find them again in previously infested areas.

“Is it just coincidence in Mountain View? I just can’t buy it,” said Carey. “Exactly at the same time and exactly the same place.”

Carey’s comments on the Medfly in Northern California are the latest volley in one of the more controversial aspects of the Medfly debate: Is the pest a permanent resident or just an occasional interloper that can be whisked into oblivion with enough malathion and sterile flies?

The distinction may seem minor to urban residents tired of being sprayed with pesticide or farmers worried that the Medfly will charge over the Tehachapi Mountains and infest their crops. But his thesis, if proven correct, could bring big changes for city dweller and growers alike.

A deeply established Medfly population, as Carey believes exists, would force the state to consider either more intensive spraying to destroy the last vestiges of the pest or simply accept life with the Medfly.

More ominously, acknowledging that the pest is established in the state would almost certainly give other states and countries reason to quarantine California crops--a prospect that farmers and officials say would change the face of the state’s agriculture industry.

“Living with the Medfly is unacceptable,” said Isi Siddiqui, assistant director of the state Department of Food and Agriculture.

Carey, in many ways, is an unlikely candidate to spark such a polarized debate over the Medfly. A 42-year-old associate professor of entomology at UC Davis, he has spent most of his career in the somewhat esoteric field of insect demographics, studying the age structures, birth rates and population dynamics of various bugs.

Detractors and supporters alike call Carey a careful academician. A usually soft-spoken man, he tends to pour out streams of thoughts when the topic shifts to Medflies.

“Jim just fits the image of the quiet, not-controversial college professor,” said one colleague. “He’s a good, basic researcher. Quiet, not overpowering, but when he gets an idea, he’s firmly committed to it.”

Carey, who first presented his views on the Medfly at a special state Assembly hearing two weeks ago, describes himself as more of a laboratory scientist than the type of entomologist who tromps through fields, looking for insects and testing new traps. But he said his study of the Medfly infestations actually requires little laboratory or field experience to understand.

All he did was plot on a map the location of every Medfly ever trapped in Southern California and a part of Northern California.

Carey found several areas that have been repeatedly infested. For example, he said, Medflies were found in Culver City in 1975, 1982, 1984, 1986, 1987 and 1988. There also were new finds in Northridge in 1980, 1988 and 1989, Baldwin Park in 1981, 1989 and 1990, and now Mountain View in 1980, 1981 and 1989.

Agriculture officials maintain that each outbreak was wiped out with pesticide spraying and then started anew by travelers or immigrants bringing infested fruit into the country. But Carey says the chances are nil that travelers or immigrants have continually infested the same places.

Instead, he believes aerial spraying has only reduced the number of Medflies to undetectable levels, making them appear as if they were cleansed from the state.

On this point, Gerald Nakayama, a peach farmer near Fresno, agrees, even though he hates the thought of Carey being right.

Nakayama has sprayed his peach trees for years with pesticides many times stronger than malathion. He said that even with hundreds of gallons of pesticide per acre, killing everything is extremely difficult, if not impossible.

Although there are differences between orchard spraying and the aerial spraying of malathion mixed with bait used to kill the Medfly, he said his experience with his own crops tells him that killing every last bug is a dream.

“Total eradication of anything is almost impossible,” he said. “Even if you wanted to kill every person in the world, you could drop tons of atomic bombs, but some people would still live.”

Roger Vargas, a U.S. Department of Agriculture researcher who is in charge of the Medfly eradication program on the Hawaiian island of Kauai, said it is conceivable for small populations of Medflies to survive malathion spraying--but not for long.

Vargas has spent 10 years killing fruit flies, and if there is one thing he’s learned it’s that they are prolific breeders.

Until coffee was planted on Kauai three years ago, he rarely found a Medfly in some parts of the island. Suddenly, the population boomed. “Now you find them all over the fields,” he said.

Based on that experience, Vargas said small pockets of Medflies could not escape detection for many generations--and certainly not nine years, as is the case in Mountain View.

Carey himself is perplexed by the delay between infestations and has no solid explanation. But Daniel Simberloff, a Florida State University biology professor whose specialty is the study of invading species, said it is possible there could be a long delay between infestations.

Small populations of insects function in radically different ways than large populations, he said. For example, it is much more difficult for them to find mates. In addition, they are more vulnerable to the large drops in population caused by outside threats, such as cold weather, predators and a lack of food.

“I won’t say the passage of time doesn’t worry me,” he said, “but it’s not inconceivable. There is nothing improbable about the Medfly staying at low levels for years.”

Proving or disproving Carey’s thesis hinges on the traps used to detect the Medfly. Even agriculture officials admit they are not very good. “It’s primitive at best,” Vargas said.

Ken Kaneshiro, professor of biology at the University of Hawaii whose research focuses on the Medfly’s mating habits, said a big part of the problem is the bait used in the traps, called Trimedlure.

The substance attracts male and virgin female Medflies, but is relatively weak. In some experiments, traps get about 2% of all adult male flies within 600 feet.

Kaneshiro said he has seen flies land on traps and not go in. He once monitored 140 marked Medflies for three days that were released within 10 meters of a trap. “We didn’t get a single one,” he said.

There is another problem with the traps--there just aren’t that many out there. There are about 160,000 traps placed throughout the state, which seems like an outrageously high number considering only about 780 Medflies have ever been caught in California.

But Carey said there are far too few to detect small Medfly populations. In Los Angeles County, five traps are placed in every square mile, which he said is akin to putting a piece of flypaper down in the middle of Yankee Stadium. “It just seems like a remote possibility that a fly is going to stumble in,” Carey said.

His colleagues on the Medfly Science Advisory Panel, most of whom disagree with him, have moved quickly to resolve the issue and recommended Wednesday a massive trapping program to test his thesis.

If the panel’s recommendation is accepted by the Department of Food and Agriculture, the number of traps in 10 one-square-mile test areas would be increased to 10,000 per square mile.

The University of California also announced the formation of a task force Monday to review Carey’s theory. The panel will be made up of experts from around the country and will take about two months to complete its review.

By the time the panel finishes, agriculture officials say Southern California’s Medfly infestation could well be over. They announced this week that if no new flies are found, most aerial spraying will end in May, leaving only Pomona and Irwindale to finish up in June.