Millions of tiny parasitic wasps are reared annually at a state lab in Riverside, Calif.
The lab is run by the California Department of Food and Agriculture as part of a biological control program to reduce populations of the Asian citrus psyllid throughout the urban centers of southern California.
The wasps come from Pakistan and were brought to the United States by University of California Entomologist Mark Hoddle, who is studying biological control methods for a host of invasive species in California.
The Asian citrus psyllid is responsible for spreading a bacterial disease called Huanglongbing, or citrus greening. It has already caused significant damage to Florida's citrus industry by killing trees and rendering citrus fruit unmarketable. Citrus greening has been found across the southern United States from Florida to Texas. One case of citrus greening was discovered in California in 2012.
There is no known cure for citrus greening, though university experts in Florida and elsewhere are working on methods to slow the disease in trees and on early detection methods that could help determine which trees have the disease to allow officials to remove trees in an effort to slow the disease's spread.