Gross out? (Activities & Oddities).

Say you're in the mood for a plump, ripe papaya. But what you find inside is a big orange mush--and it's wriggling! Fistfuls of fruit fly larvae (wormlike developing young) are digging tunnels all over the sweet flesh. Turned off? Not geneticist (gene scientist) Donald McInnis of the U.S. Department of Agriculture's Tropical Plant Pests Research Unit in Hawaii. "It makes me want to solve the problem," he says.

Papaya spells big business for the Aloha State. And infestation by four invader species (non-native species) of fruit flies--Oriental, melon, Mediterranean, and Malaysian--has cost farmers millions of dollars in crop damage. "We're not talking about those little things you find flying around rotting fruit," says McInnis. Those are vinegar flies--their larvae feed on yeasts produced on the surface of fermenting fruit. The Hawaiian invaders, however, are true fruit flies and belong to another family. The female purposely punctures the skin of ripening fruit and vegetables to lay hundreds of eggs inside--which results in a wormy waste.

To help clobber the pests, McInnis breeds sterile (infertile) males of the melon fly in the lab. In the wild, male and female pupae (stage before adulthood) feature a brown cocoonlike covering. In McInnis's sterile strain, the female has a white casing. Using a high-speed, color-sorting machine, he separates males from females. Only males are released into the wild. "We want sterile males to mate with wild females," he says. This way, eggs can't fertilize. "It seems to be working," McInnis says. There's a big drop in Hawaiian fruit-fly populations.