For the fieldworkers at the USDA's Subtropical Horticultural Station, Wendy Chung and her portable Sears car vacuum must have been quite a sight. With the Miami summer sun edging its way up in the sky and the vacuum cleaner nozzle poised for action, Chung stalked through a guava grove, ready to suck up any slow-moving Caribbean fruit fly that might cross her determined path.

Well, okay. Not just any Caribbean fruit fly.

Chung had specific requirements for her Anastrepha suspensa: female and "absolutely full with eggs," she says. "The way I was running my experiment, that was essential."

"Maybe one out of every 10 flies would meet the qualifications . . . I would have to collect 20 flies every morning, and depending on how the day was, it could get very frustrating," recalls Chung.

This went on all last summer. But come September, Chung's vacuum cleaner was off and she was back at Miami Killian Senior High, first in her senior class of 847 and hoping to attend Harvard.

How can Harvard resist a young woman who spends eight months studying the ova position of the Anastrepha suspensa and the different stages of ripeness in the guava? The Science Talent Search certainly couldn't. Eventually, Chung's experiment might help to protect fruit, including Florida's citrus crops, from infestation by Caribbean and Mediterranean fruit flies. And for that Chung is one of 40 talented finalists in the 45th annual competition for high school seniors. Tonight, at a banquet at the Mayflower Hotel, the finalists' five days of special events and honors culminate in the distribution of $140,000 in Westinghouse science scholarships and awards.

How could Harvard resist STS finalist Daniel John Zigmond? He's into eating disorders -- specifically, the kind that keep the C. elegans (short for Caenorhabditis elegans) from digesting their protein. Those are worms, and Zigmond has spent about a year with them, in Dr. Lewis Jacobson's laboratory at the University of Pittsburgh.

"Even though the results I got will be able to help other people," says Zigmond, "I wasn't really doing it as a great humanitarian gesture, but because it is something I enjoy."

The enjoyment began as a perfectly straightforward study of three mutations: lon-1, daf-4 and unc-32. "These worms are very good for genetics," explains Zigmond. "They have a life span of about five days, so in three days you get a whole new generation. It's very easy to watch how things change in successive generations."

Standing in front of his display, in the Exhibition Hall of the National Academy of Sciences, Zigmond points to a little chart -- a C. elegans family tree: "This would take only a few weeks to go through it. If you used mice it would take years. If you used humans, of course, it would take centuries." Zigmond is only 16 years old, but still he doesn't have that kind of time.

Few of the science projects on display this past weekend were any more accessible to the nonscientist than Chung's and Zigmond's. Finalist Jessica Boklan spent her summer in a laboratory freezing embryos. Then two weeks before the competition's deadline, she switched from biology to math and devised an algorithmic approach to the construction of reversal products. "It's just a rule," she says. It looked simple at first: 264 times 693 equals 396 times 462. But the proof never got any easier. Written out on poster board, and looking like high-tech hieroglyphics, the proof would make any math-anxious adult crumble.

"I'm not so much a mathematician," says Boklan, modestly. She just cut her teeth on arithmetic: Boklan spent her early childhood waking up in the morning, reaching under her pillow and pulling out subtraction and addition problems left during the night by her fun-loving father. "It was fun," Boklan admits. "When you are talking about a 3- or 4-year-old, borrowing in subtraction is a big thing."

Andrew Lawrence Feig, an 18-year-old from Los Angeles, is brilliant, but otherwise quite normal. He's also handsome. He speaks in sentences of perfectly intelligible, carefully chosen words. But soon enough, when things really count, syllables come spilling out to explain the title of his STS project, "Monoclonal Antibodies Specific for the N-myc Oncogene Product."

Feig broke the title down, sort of: "The N-myc oncogene is found in neuroblastoma. The oncogene product is the protein encoded by this oncogene. A monoclonal antibody is an antibody that we have produced through a fusion of two different cell types, a myeloma cell (which is a malignancy) and spleen cells from an immunized mouse, which then produce . . . " confusion.

Feig wants to go to Harvard for more biochemical and molecular fun.

These days Beth Meyerand, 17, from Glastonbury, Conn., is studying "the effect of heavy water on the glucose breakdown reactions in unicellular microorganisms."

"I can relate to that," says one of her waggish cofinalists.

But the young fellow doesn't really have to "relate" to glucose breakdown reactions because that's not what brought Meyerand to the STS finals. Wave energy got her here. It took her four years of "diagrams, models and many machines that did not work" before she "came up with a device that did successfully generate energy." Now she has a patent attorney and a patent pending.

"I like to go to rock concerts and that stuff," says Meyerand. "And, you know, I am pretty much like anybody else, just instead of going to the lake in the summertime I sit in the garage and build wave machines."

Watching your friends take off for the lake or for Europe can be a drag. "My project would pretty much chew up my summers . . . There were times when my fifth model fell apart, or something, and I considered just throwing the whole thing away and going out and having fun."

Sometimes, sitting alone in the garage and, as she puts it, "hacking away at a generator," Meyerand never actually thought the whole wave thing would work. There had, after all, been some inauspicious moments:

"One night, at about 11:30, I was working in the garage. I learned one important thing. You never use a saber saw to cut a hollow, steel garbage can. It sounds like the Mafia is going through the neighborhood with a machine gun. I had the whole neighborhood out in their pajamas, running at our house. They thought we were blowing it up or that I was shooting my parents or something.

"I got the saw blade jammed in the garbage can. I broke it."

Meyerand plans to go to Harvard