Category Archives: Huanglongbing bacteria

My parents have a glass of freshly squeezed orange juice every morning. They believe in its health benefits. My mom claims that she did not have a cold ever since they started their day with a glass of fresh orange juice. They buy huge boxes of oranges every week at the local market.

A few weeks ago they stopped. The oranges were too expensive.

A disease called Citrus Greening – also known as Huanglongbing (HLB) or yellow dragon disease – next to environmental effects (drought in Brazil, hurricanes in Florida, dry summer in Spain) – diminishes our oranges and spurs the prices. Named for its small, partially green fruits, Citrus Greening has ravaged orange fields in Florida and the US East Coast. Infected trees produce misshapen fruits with bitter juice and dark aborted seeds that drop prematurely. Eventually the tree stops bearing fruits and dies.

Misshapen, green orange fruits from a Citrus Greening – infected tree.

Citrus Greening is transmitted by a tiny mottled brown insect – the Asian Citrus Psyllid (Diaphorina citri). The psyllid feeds on the stems and leaves of citrus plants. Not limited to orange trees, it also feasts on grapefruits, pomelos, mandarins, lemons and lime. While it feeds, it damages the young citrus leaves. But that is not what it makes it so nasty.

The nasty thing about the Asian Citrus Psyllid is that it can take up a bacterium in its body and transmit it to the next citrus plant it feeds upon. This Huanglongbing (HLB) bacterium can kill a citrus tree in as little as five years and there is no known cure and no resistant citrus plant.

Asian Citrus Psyllid.

Both the Asian Citrus Psyllid and the HLB bacterium originate from Asia or India and then spread to other parts of the world where citrus is grown and where they have no natural enemies. The Asian Citrus Psyllid – and with it the HLB bacterium – can easily move by wind from one citrus-growing area to another.

Researchers in Florida, Brazil and California are working hard on breeding HLB-resistant citrus trees and developing chemical controls with insecticides. Insecticides however have the disadvantage that they are also toxic to honey bees.

The most promising weapon against the Asian Citrus Psyllid is its natural enemy – the parasitic wasp Tamarixia radiata. Females of this tiny wasp – not bigger than the dot at the end of this sentence – lay their eggs underneath the psyllid nymphs, and after hatching, the parasitoid larvae attack and kill the psyllid.

Sounds brutal? Might save our orange juice!



“Asian Citrus Pyllid and Hanglongbing Disease”. UC Davis. August 2013

Pictures: Wikipedia