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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.


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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