Lerp Psyllids on Eucalyptus Trees
In a trend that sees no stopping, the 1990’s brought many new pests to the United States, and several of these have surfaced in California. The eucalyptus trees encompass many species of hardy, evergreen trees that are native to Australia. They thrive in the moderate climate in much of California, and for many years had virtually no pests attacking them.
Now, however, there are several species of insects causing problems for these trees, and one group is the “psyllids”, also called Jumping Plant Lice. These insects are related to aphids, but are more mobile in the adult stage and do not have the two little pointed horns at the end of the abdomen, called “cornicles”, that aphids have. In 1991 the “Blue Gum Psyllid” was discovered in the Monterey area along the coast, and in 1998 the “Red Gum Lerp Psyllid” showed up in the Los Angeles area. In both cases these foliar pests spread very, very rapidly throughout the state.
Now, this is a pretty unusual name for a bug – a “lerp” – so what exactly does that mean. Well, Lerp refers to the early stage of the bug, and the little white capsule that it creates over itself on the leaf. These insects feed by inserting their mouth, a sucking straw, into the leaf, and sucking out liquids from the leaf. Much of this liquid is sugary, and the psyllid nymphs pass the liquid through their system, excreting a sticky substance called “honeydew” out their back ends. We see this same honeydew from aphids, as it coats sidewalks or the tops of our cars with a thin layer of sticky material. The word “lerp” actually has its origin as an Aborigine word that described these little structures.
However, with the Lerp Psyllid the honeydew forms a crystalline shell over the bug, and eucalyptus leaves can virtually be covered with the lerps, dozens of them on every leaf on the tree. As many as eight species of eucalyptus trees are known to be attacked by this pest, but it is the Red Gum Eucalyptus – Eucalyptus camaldulensis – that seems to suffer most. Intensive infestations of the psyllid have resulted in extensive drop of leaves, branch dieback, and even death of some trees already under stress.
What are some signs of infested trees?
The first thing you might notice, if you have eucalyptus trees that are infested, is that the bottoms of your shoes seem to be getting coated with tiny, sticky, white spots. These are the “lerps” that have fallen off the tree, that previously were forming a protective cover over the nymph of the psyllid. They fall off the tree as the nymph reaches the adult stage or a heavy wind blows. They absolutely are not dangerous, but they certainly are a major nuisance on your feet or on your windshield.
If you then look up into the tree you will quickly notice the white spots all over the leaves, and if you were to take your fingernail and pick off one of the lerps you will notice a tiny, wingless insect underneath. Their numbers increase dramatically in the summer, and in the rains of winter they tend to wash off, leaving the leaf somewhat dirty looking. Honeydew on leaves also allows growth of a black layer of mold called “sooty” mold, and this may cover the leaves as well. The mold is not a disease of the tree, and causes almost no damage to the tree, but it is unsightly and can be washed off with a spray of weak soapy water.
What is the danger to my trees?
Apparently not much. If your trees are in otherwise good health there seems to be relatively little damage done to them by the Lerp Psyllid. There is another recent imported pest that has a far more serious effect on eucalyptus, and that is the Eucalyptus Long Horned Borer, a large, beautiful, but damaging beetle whose larvae bore under the bark of the tree and potentially can kill it. Should this pest be attacking your trees and putting them under stress, the added assault by the Lerp Psyllid on the leaves could be a problem.
Doesn’t anything stop the Lerp Psyllid?
As with any organism there also are “natural” enemies of the Red Gum Lerp Psyllid, but they live in their “natural” environment, which is Australia. Intensive studies are being conducted to determine just what those enemies are and, if possible, import them to California to control the pest there. This is always touchy, and must be one with the greatest of caution. Commonly the natural enemy of an imported plant pest turns out to be a tiny parasitic wasp. Those which were the enemies of the Blue Gum Psyllid were introduced, raised by the zillions, and released to the environment, where they very effectively controlled the problem in this country.
However, imagine the damage that could be caused if we brought in a second new species of animal to control the first species, and that second species turned out to be a bigger problem, now unleashed on a new environment. Imagine the problem if it turned out that the tiny parasitic wasp that could control the Blue Gum Psyllid also took a liking to all the ladybugs, or some other beneficial insect in California – the eggs of Praying Mantids, perhaps. So, use of beneficial insect controls requires very careful study prior to their use.
Otherwise, there are numerous natural predators of sucking insects such as the Red Gum Lerp Psyllid, and some of those known to attack these critters are:
- Ladybird Beetles (lady “bugs”) – Two Spotted Ladybird Beetle, Convergent Ladybird Beetle and others
- The Minute Pirate Bug
- Green Lacewings and Brown Lacewings
- Birds – chickadees and bushtits have been observed feeding on them.
- Syrphid flies – the pretty little wasp mimics, that we call flower flies
What should I do if my trees are infested?
Well, as hard as it may be to do so, your current best course is to do …….nothing. By this is meant do nothing as far as spraying the trees with insecticides, because this really is going to do very little to help. The Professional Pest Control companies do have several chemical tools available to them that seem to help prevent or eliminate the Lerp Psyllid, but this might best be used if your trees are at risk. Some of these are used as a soil injection rather than a spray, and the chemical is absorbed by the tree’s roots. This offers a low impact method that gets the chemical inside the leaves where the psyllids can ingest it.
The University of California is working quickly to identify the parasitic wasps that would control the Red Gum Lerp Psyllid, and currently feel they have identified a tiny parasitic wasp that is specific to this pest. This wasp is named Psyllaephagus bliteus – a very appropriate name, for the first part of it means “psyllid eater”. It is in the approval stage for rearing and releasing, and test areas already are being tried. University of California is very optimistic that it will be successful, but results are slow, as the wasps will spread on their own throughout infested areas, and it may be years before populations of the Lerp Psyllid noticeably crash.
Other than this, just ensure your trees stay in good health. Do Not Fertilize eucalyptus trees, as this causes greater foliage production and encourages larger populations of the psyllids. Appropriate “supplemental” watering could be provided to the trees during periods of extended non-rainfall, to ensure they stay healthy and not in a stressed condition.