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Eucalyptus pests

Eucalyptus are some of the  most recognized trees in today's landscapes.  Since around 1860 they have been imported into the San Joaquin Valley for use as firewood, windbreaks, railroad ties, lumber and posts.  For nearly 130 years these trees were free of any insect pests in California.  Now, during the last 15 years, at least 18 different pests of this Australian tree have entered into California, three of which have been found in the southern San Joaquin Valley.

Red Gum Lerp Psyllid

Adult Red Gum Lerp Psyllid
Adult Red Gum Lerp Psyllid
.  The red gum lerp psyllid is one of many psyllid species that attack eucalyptus.  They are recognized most readily by the white lerp , or house, that they secrete over themselves for protection.  Lerp psyllid at high densities become a significant problem due to the honeydew they secrete.  This sticky liquid falls from the leaves to the ground where it makes a sticky mess.
Lerps (or houses) of the red gum lerp psyllid
Lerps (or houses) of the red gum lerp psyllid
Large numbers of psyllids can also stress a tree to the point that it sheds its leaves.  While this damage does not generally kill the tree, stressed trees become more susceptible to other pests, specifically the eucalyptus longhorned borer.

There is little that property-owners can do to control red gum lerp psyllid.  Neither cultural controls like watering or fertilizing trees, nor insecticides have proven useful against this pest.  The only successes thus far have been through biological control efforts to import and release parasites from Australia that feed on this pest.  Thus far, releases have been made throughout the state of California, including Kern County.  Releases in Kern County took place in July of 2002 in Edison.  Recoveries by the end of the year were made at least as far away as Rosedale.  Some surveys will be done in the late spring or early summer of 2003 to determine if the parasites were able to make it through the winter.  Parasitized psyllid

Exit holes where parasites have emerged from the psyllid nymph under a lerp.
Exit holes where parasites have emerged from the psyllid nymph under a lerp.
can be recognized by the small, round holes in the side of the lerp, and by the remaining mummy of the psyllid nymph left behind when the lerp is removed
Parasitized Red Gum Lerp Psyllid nymph.
Parasitized Red Gum Lerp Psyllid nymph.
.

Parasites have most readily become established in coastal areas of the state, where temperatures are more moderate and releases began two to three years prior to those in the San Joaquin Valley.  An update on the statewide efforts to establish parasites that feed on lerp psyllid can be found at http://www.cnr.berkeley.edu/biocon/dahlsten/rglp/index.htm

 

 

Red Gum Lerp Psyllid Life Cycle (click to see larger images)

Red gum lerp psyllid eggs can be found in clusters on the leaf surface
Red gum lerp psyllid eggs can be found in clusters on the leaf surface
Immature psyllid emerge from the eggs and construct a protective lerp (or house) over the top of them.
Immature psyllid emerge from the eggs and construct a protective lerp (or house) over the top of them.
The first strand of construction  material is complete.
The first strand of construction material is complete.
A matrix of strands build the framework for the lerp.
A matrix of strands build the framework for the lerp.
The matrix will begin to fill in to form a complete covering.
The matrix will begin to fill in to form a complete covering.
The newly-secreted lurp is completed.
The newly-secreted lurp is completed.
Nymphs will pupate under the lurps.  Notice the newly-hatched nymph in the center bottom of the picture.
Nymphs will pupate under the lurps. Notice the newly-hatched nymph in the center bottom of the picture.
Pupal psyllid will emerge into adults and can often be found crawling on the leaf surface.
Pupal psyllid will emerge into adults and can often be found crawling on the leaf surface.

Additional information of lerp psyllid history, identificaiton, life cycle, damage and management can be found by downloading the UC Publication, Pest Notes: Red Gum Lerp Psyllid .

Eucalyptus longhorned borers

Adult eucalyptus longhorned borer
Adult eucalyptus longhorned borer
Eucalyptus longhorned borers (ELB) are two species of bark beetles that were first introduced into California in the 1980's and around 1995 respectively.  So far, only the second of these two beetle species, Phoracantha recurva, has been found
Larval galleries under the bark of Eucalyptus
Larval galleries under the bark of Eucalyptus
in the southern SJV.  Pregnant female beetles of this species are attracted to and lay their eggs on stressed eucalyptus trees.  Eggs hatch into larvae that tunnel burrows into the cambium layer of the tree.  In many cases, larval galleries can girdle a tree completely disrupting the tree's ability to transport water from the roots to the above-ground portion of the tree.  Girdled trees can go from healthy to completely dead in approximately three weeks.  It is estimated that this pest has killed approximately 30,000 eucalyptus trees in Los Angeles County.  Infestations in wood can be determined by sap flowing from the living tree, or by the presence of larvae under the bark or by pupae at the base of pupal plugs that they will chew through to emerge in the spring or summer.

Pupal plugs of the eucalyptus longhorned borer
Pupal plugs of the eucalyptus longhorned borer
The best way to protect eucalyptus from longhorned borers is by keeping the trees healthy and by promptly removing infested wood. Tree health is important, as larvae of the beetle cannot survive in healthy eucalyptus trees. They essentially 'drown' from the large amounts of fluids that fill their larval galleries as they bore through healthy tree tissues. The removal of infested wood is essential, as larvae will continue to develop and emerge into adult beetles that will continue infesting the same and adjacent trees. Fresh wood piles are a favorite location for these beetles, and should be  promptly burned, chipped, or buried if they are infested.

Wood piles provide a good habitat for longhorned borers, and facilitate reinfestation into eucalyptus groves
Wood piles provide a good habitat for longhorned borers, and facilitate reinfestation into eucalyptus groves
There are efforts under way at UC Riverside to mass rear an egg and a larval parasite for ELB.  The laboratory of Dr. Tim Paine is currently producing as many parasites as possible, and plans to release both parasite species into Kern County in the summer of 2003.  If they become established, the egg parasite is more effective against P. semipunctata (the species that hasn't been found in Kern County) than against the species that we do have, but should exhibit some control.  The larval parasite will utilize either species as a host.    For more information on ELB history, identification, life cycle, damage and management, please consult the UC Publication,  Pest Notes: Eucalyptus Longhorned Borer .

Eucalyptus tortoise beetle .  This leaf-feeding beetle was first found in California in 1998 in Riverside County.  Since then, it has spread to and been found in most regions of the state where eucalyptus is grown, including Kern County.  Tortoise beetle adults are the size and shape of a large lady beetle, and are brown with mottled spots.  Larvae look like small caterpillars with six true legs.  They are reddish brown to green and have a black head.  Damage from the beetles is easily recognized as irregular notches along leaf edges.  So far, damage in the San Joaquin Valley has been very minimal to non-existant.  In other parts of the state, they have been known to nearly defoliate entire trees.

More information on the eucalyptus tortoise beetle can be found by downloading the UC Publication, Pest Notes: Australian Tortoise Beetle .