The Asian Citrus Psyllid, an invasive insect pest from Asia, has carried Citrus Greening disease to Florida’s citrus orchards. Can California repel these invaders?

Orange Tree in Florida Photo: Steve Webel

The Asian Citrus Psyllid has invaded the United States. Marching west from Florida, it is now poised to strike California’s citrus groves.

Yet the Asian Citrus Psyllid is not, itself, the greatest threat. Like the rats that carried bubonic plague throughout Europe, the psyllid is more dangerous as the carrier of a disease. “Citrus Greening”, or “Huanglongbing” in Chinese, is fatal to citrus trees.

Introducing the Asian Citrus PsyllidPhoto: USDAgov

The Asian Citrus Psyllid, or Diaphorina citri Kuwayama, is about the size of a grain of rice. The psyllid family is large: there are many small insects with strong hind legs that jump onto, and feed on, plants. Sometimes called “plant lice”, this family includes boxwood psyllids, hackberry gall psyllids, and potato or tomato psyllids. This specific psyllid, the Asian Citrus Psyllid, is a native of southern Asia. It arrived in Brazil well before 1950, but was only reported in Florida in 1998.

Besides Florida and California, the Asian Citrus Psyllid counts Hawaii and seven southern US states as “home away from home”.

The Life Cycle of the Asian Citrus Psyllid
Photo: USDAgov

The eggs are about one-third of a millimetre long and shaped like tiny almonds. As they mature, their color changes from pale through yellow to orange. The eggs are laid on the growth tips or new leaves of plants, so the nymphs will hatch right on top of their food supply.

Nymphs grow through five stages, finally becoming about 1.7mm long. Nymphs only eat the tender new growth of a plant, generally the leaves. They move in a fairly slow and deliberate manner, retaining the yellowish orange color scheme that marks mature eggs.

Taking less than three weeks to mature into adults, the Asian Citrus Psyllid might have over 20 generations in a single year under absolutely ideal weather conditions. The adult might live several months with its brownish coloration. Adults are fully capable of jumping; this is one way to distinguish them from slower aphids.

Damage Caused by Feeding

People mainly focus attention on the damage caused by the Asian Citrus Psyllid. The direct damage is far beyond the rather large amount of sap this psyllid drinks from a tree.

As it feeds, it injects saliva that impairs the growth of a leaf or twig. It also drips honeydew from its body; this sticky goo acts as a growth medium for “sooty mold”.

This damage is not too severe in a mature citrus tree, but is detrimental to saplings.

The Dreaded “Citrus Greening” Disease

Green Citrus Disease Photo: USDAgov

By far the worst damage caused by the Asian Citrus Psyllid is due to “Citrus Greening” disease, “Huanglongbing”, or Candidatus Liberibacter asiaticus.

Infected citrus trees will exhibit mottled leaves and yellow shoots. Growth will diminish, twigs may die, both leaves and fruit may drop. Surviving fruit may be misshapen, small, hard, bitter and fail to show a “ripening” color.

Current Countermeasures for the Asian Citrus Psyllid

Florida has a protocol for dealing with infestations of this invasive insect, which includes monitoring, insecticides and biological controls. California’s citrus growers are paying for a monitoring program and quarantine any infestations that are found. As of mid-July, 2011, California has not found any cases of Citrus Greening disease. Let’s hope it stays that way.

Image of Healthy Tangerine Tree Photo: andydr

Sources: 1, 2, 3