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For my March feature on a disease that is threatening the U.S. citrus industry (“The End of Orange Juice”), I spent time with researchers and growers who are working to stop this bacterial illness, which leaves fruit green and bitter and kills trees. Known as huanglongbing (HLB) -- Chinese for yellow dragon disease -- it is caused by bacteria that hide in the salivary glands of invasive insects known as Asian citrus psyllids. The pests arrived in the U.S. in the late 1990s and have spread the disease by injecting germs into plants as they feed on sap from their leaves. There is no cure for the disease.
Huanglongbing, which is also called citrus greening, was first spotted in Florida—the heart of America’s orange juice industry -- in 2005 and has since spread to Georgia, South Carolina, Texas and southern California. Nearly every commercial grove in Florida has been infected, costing the state billions of dollars and thousands of lost jobs. Late in 2012, the first Asian citrus psyllid was spotted in California’s commercial groves--which grow nearly 80 percent of all the fresh oranges produced in the U.S.--most likely heralding the arrival of the disease.
Scientists are looking at many different approaches to managing and eradicating the disease. Many say the only long-term solution will be genetic modification, which is still years away. In the meantime, entomologists are using biological control -- the practice of releasing living organisms to prey on pests -- as a means of keeping psyllid populations in check in residential areas where pesticide sprays have failed. (In Los Angeles, for example, psyllids multiplied so quickly on backyard citrus trees that state authorities couldn’t keep pace). Mark and Christina Hoddle, entomologists at the University of California, Riverside, have imported tiny wasps from Pakistan to feast on Asian citrus psyllids and have released them at more than 100 sites in Los Angeles, Riverside, and Orange and San Bernardino counties. (The wasps do not sting humans). In this video, Christina releases a vial of wasps--29 females and 15 males--on a curry bush in the parking lot of a Los Angeles hotel. (Curry is a citrus relative). The site may seem random, but in fact the Hoddles used state data to identify this site as being particularly infested with Asian citrus psyllids, which Christina calls “ACP” for short in this clip. She also talks about having previously scouted the shrub to make sure it has plenty of psyllid nymphs at the 4th and 5th instars, which are the two life stages that the wasps attack.