San Francisco — California's helicopter war against the Mediterranean fruit fly was thought to be going so well three weeks ago that Medfly control officials planned to halt aerial spraying in early November.
But a series of recent events -- especially the discovery Oct. 30 of two fertile male Medflies in an area thought to be ''clean'' -- have those in charge of the program shaking their heads.
''Something like this gives you pause,'' says Medfly project manager Jerry Scribner. ''Once again we are underestimating the fly a bit.''
The two flies found last week in Mountain View, part of the original infestation area, emerged from the ground 70 days after the first generation of the pests was discovered in the area. This confirmed findings of University of California entomologist Richard Tassan. Using a computer model developed on the Berkley campus, he demonstrated that the Medfly's life cycle in parts of the San Francisco Bay Area could stretch for 76 days depending on weather and other factors.
This meant that at least in some areas, the control plan of aerial spraying for two 10-week Medfly life cycles might fall far short of eradicating the pest. Those two Mountain View flies, Mr. Scribner says, show that Dr. Tassan's theory was ''right on the money.''
That discovery was the latest in a number of developments in the Medfly situation:
* On Oct. 23, Scribner announced that -- aerial spraying would be phased out in a 710-square-mile area of Alameda, Santa Clara, and Stanislaus counties by Nov. 15.
* On the same day, Gov. Edmund G. Brown Jr. appointed a seven-member Pest Response Task Force to enable the state to react quickly to any future Medfly infestation. He also named a 17-member group of government, farm, business, and scientific leaders to look into better methods of preventing Medfly outbreaks.
* On the night of Oct. 23, a Medfly program helicopter lost in fog while returning to home base with empty spray tanks crashed in a residential area of Fremont. The pilot was killed, residents of a house the craft hit were slightly injured, and public concern over the hazards of aerial spraying was rearoused.
* There were a few other discoveries of Medflies in October, which were not unexpected, but altered eradication plans somewhat.
* In recent days, rain -- at times heavy over the Medfly quarantine area -- washed away some of the pesticide and delayed spraying in some areas.
Events since last July seem to have taken the Medfly out of Governor Brown's political soup. A bitter aftertaste may long remain for some -- especially agricultural interests. But Brown, after initial resistance to aerial spraying, appears to have done all the growers could reasonably expect him to do in the effort to rid the state of the pest.
No one now doubts that Medflies will return next spring. And there is growing concern about the prospects of complete success in eradicating the fly through current methods. Thus Brown's new committees might listen to another University of California scientist, invertibrate pathologist George O. Poinar Jr., who is convinced he has found a very effective Medfly eradication tool -- nematodes. Mr. Poinar says laboratory tests have convincingly demonstrated the effectiveness of tiny parasites in destroying fruit fly pupae in the soil.
He has been trying, so far unsuccessfully, to get the state to set up a field experiment. A Berkeley firm is ready to mass produce the nematodes. Poinar now may find concerned state officials more receptive to his proposal.