State Gambles That Sterile Flies Can Do the Job : Medfly: Agriculture officials are about to attempt a tactical shift in the battle, replacing the aerial spraying of malathion.


Nori Tanaka, a scruffy, gray-haired entomologist, trudges through a converted tuna-packing shed, flicking flies off his face. It is just before the dawn of another humid day. In one corner of the ramshackle building, workers grind out sticky, brown fly food in a cement mixer. In another, fly pupae are sifted through a makeshift device of cardboard, old broom heads and wire mesh.

Tanaka reeks mightily of sugar, yeast and other odors that come with the job of mating insects. A cloud of flies surrounds his face. He gazes about the shed, proudly surveying the noisy scene. A few flies float in his coffee cup. He drinks it anyway.

"It takes a certain man," Tanaka says, "to be a rearing man. You have to dream this stuff."

Tanaka is the country's foremost fly "rearing man." His domain is the California-Hawaii Agriculture Medfly Project--a facility that throughout this summer will be the most important outpost in the state's war against the Medfly in Southern California.

Agriculture officials are about to attempt a tactical shift in their effort to eradicate the Medfly, replacing aerial malathion spraying with the release of millions of sterile flies. If all goes well, and if no fertile flies are found by the end of next month--a major qualifier--the sterile fly releases will replace the controversial pesticide program over all but about 10% of the large infestation area.

Devised 40 years ago, the simple concept calls for the release of millions of sterile Medflies in successive waves. The steriles, made so by exposure to radiation, are intended to numerically overwhelm their sexual competitors in mating with wild flies. With no offspring from the mating, the wild flies eventually will die out. Or so the theory goes.

An El Cajon infestation of the Mexican fruit fly will also be attacked with sterile flies, produced at a facility similar to Tanaka's in the Rio Grande Valley of Texas. After at least three aerial sprayings with malathion, about 20 million sterile Mexflies are to be released each week in San Diego County.

Largely undetectable by the public, harmless to the environment and, as far as anyone can tell, harmless to people as well, the sterile Medfly approach not only will eradicate the pest, agricultural officials believe, but will also end the public outcry over pesticide spraying.

Much of the task hinges on Tanaka, who as operator of two of the three major sterile breeding facilities here must be able to deliver the irradiated flies in sufficient numbers to support the campaign. It is a difficult challenge; shortages of sterile flies, coupled with a rash of Medfly discoveries over the last few months, already forced the state to retreat from its original May 9 deadline to end spraying.

There are other hazards. Improperly sterilized flies can be explosively dangerous to the eradication campaign; some officials still maintain that this occurred with a batch of South American flies brought in to battle the 1981 infestation. There have also been complaints from residents that the clouds of sterilized flies have an uncanny knack for knocking into freshly painted walls.

And the central question--do the sterile releases work?--remains less than resolved in scientific circles. No scientist can explain precisely how the approach works, nor can they say with certainty if it will succeed on the scale to be attempted in Southern California.

"There's a lot we don't know," Tanaka said in an interview last month. "I believe it works, but there have been so many failures, too."

Tanaka, who has been rearing flies for four decades, is considered the dean of sterile Medfly production. Most of the techniques and equipment used in the United States for raising Medflies were developed by Tanaka, a born tinkerer who constantly prowls the facilities in a grimy T-shirt, checking on food mixtures or adjusting the temperature in the rearing rooms.

Since the beginning of the year, he has spent almost every waking hour inside the tuna shed, located in an industrial section of Honolulu, breeding the millions of flies demanded by California.

"This is the only thing I know," he said. "It's my whole life."

The state's new battle plan is actually a return to a strategy that agriculture officials originally intended to use last summer, before the Medfly outbreaks exploded throughout the Southland.

When the first Medfly infestation was detected last July 20 in Elysian Park, officials believed that the outbreak was an isolated case and could be quietly eradicated with one or two aerial spraying followed by the release of sterile flies.

But by December, the Medfly had spread through 200 square miles of Los Angeles and Orange counties and state officials admitted that had exhausted their supply of sterile Medflies. Their only alternative was to spray wide sectors of Southern California with repeated aerial doses of malathion, deploying steriles in only a few pockets of infestation.

For the last four months, the state has pushed to increase sterile fly production and is now receiving about 300 million sterile flies a week--enough to treat about 300 square miles of the infestation.

Tanaka's two breeding facilities turn out a weekly supply of about 150 million sterile Medflies. Another 120 million are arriving from a breeding facility in Mexico, along with about 40 million from a third rearing facility in Hawaii. The flies are raised in places where the pest is already established.

The process begins in the breeding facilities where the flies are raised, dyed (to make sure they are not confused with wild flies), sterilized by exposure to radiation, and then shipped to California in long, sausage-like bags that each contain thousands of fly pupae.

The adult flies emerge after arrival and are then scattered by truck or airplane throughout an infestation zone at a rate of about 1 million every square mile every week. Prior to the introduction of steriles, an infested area usually is sprayed once or twice with malathion to reduce the wild fly population.

The flies are released for three generations--about three or four months during the summer.

It's a virtually benign treatment that seems to make scientific sense, although the record has been less than perfect.

"There's no reason why it can't eradicate an insect," said Edward F. Knipling, the now-retired originator of the idea. "I don't know how you can miss."

Knipling was a junior entomologist with the U.S. Department of Agriculture when he hatched the idea of using sterile insects as a weapon of eradication in the 1930s. At the time, much of the southern United States was infested with a pest called the screw-worm fly, whose burrowing larvae killed livestock.

His colleague jeered the idea. Knipling himself thought of it as a "long shot."

It took nearly 15 years before Knipling heard of a way to sterilize flies using radiation. The series of eradication programs he eventually launched cleansed the United States and Mexico of the screw-worm pest. The program still continues today and is now poised to push through Central America.

Some scientists say generally that California has never had much luck in using sterile techniques against the Medfly. James R. Carey, a UC Davis entomologist and one of five scientific advisers in the state's eradication campaign, said sterile Medflies have been released in this state eight out of the last 15 years and yet infestations continue to crop up, sometimes in the same place over and over again.

Carey and other scientists agree that the technique has succeeded each time in substantially reducing the Medfly population but, they ask, did it wipe out every last vestige of the pest?

"It's a very good tool for suppression of a population. The evidence of that is clear," said Ronald Prokopy, an entomologist at the University of Massachusetts and an expert on the Medfly. "But eradication, that is a different story. I have no idea."

Little is known about how the technique actually works. For example, scientists are not certain about such fundamental questions as whether it is the sterile male flies, sterile females, or both, that break the reproduction cycle.

Kenneth Kaneshiro, director of the Hawaiian Evolutionary Biology Program at the University of Hawaii and a Medfly expert, said that in the wild, lab-reared flies are lousy at performing their species' complex mating rituals, are not good at defending their territory, and they are downright miserable at finding mates. "Sexually inadequate," Kaneshiro said.

The qualities of sterile flies aside, there are constant problems in rearing them in the huge quantities needed for an eradication program.

When state Department of Food and Agriculture Director Henry J. Voss announced in March his decision to replace spraying with sterile fly releases, a key to his plan was receiving millions of flies from a just-completed U.S. Department of Agriculture facility in Waimanalo, Hawaii.

The $7-million Waimanalo facility, the one Hawaiian facility not run by Tanaka, is a modern, concrete-and-glass building packed with the latest high-tech fly-rearing equipment. Its insides bristle in shades of stainless steel and plastic. It was designed to produce up to 500 million sterile flies a week. So far, it has been lumbering along at a pace of 40 million a week.

EL CAJON PROTEST--The City Council voted unanimously to oppose plans for aerial spraying of malathion to stop the Mexican fruit fly. B1

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