In a lemon grove in Riverside, California, a half dozen beige mesh tents rise above the fruit trees. Within each tent a solitary lemon tree bustles with invaders from another continent: small insects called Asian citrus psyllids. They're potential carriers of a plague that could decimate California's citrus groves. But scientists here are deliberately breeding them—in order to breed an antidote.

"Warning," read signs posted on the tents in English and Spanish. "Wasps inside."

A lot is riding on the little bugs.

Citrus greening, as the citrus disease is called, has already destroyed 90,000 acres of trees in Florida groves. Most kinds of citrus, from lemons to oranges to grapefruit, are susceptible. California's two-billion-dollar industry, which grows 80 percent of the citrus