Horticultural Subjects Archive

Psyllid Infestation on Stanford Campus

The Eucalyptus pest attacking several varieties of Eucalyptus on Stanford Campus was first discovered during the summer of 1998. The small insect, the Red Gum Lerp Psyllid, (Glycaspis brimblecombei), is native to Australia. The psyllid attacks the red gum, (Eucalyptus camaldulensis) as well as more than 25 additional varieties of Eucalyptus. A list of the varieties can be found on the Red Gum Lerp Psyllid website.

Female psyllids lay their eggs on the surface of Eucalyptus leaves. The emerging nymphs create a protective conical shaped formation called a lerp. The lerp is made form honeydew secreted by the nymphs. Ants are often attracted to the lerps to feed on the honeydew. The honeydew creates a nuisance when defoliated leaves coated with the sticky substance fall on cars or are tracked by foot into nearby buildings or homes. The damage to the leaves caused by the feeding nymphs results in the death and defoliation of the leaves. Over time the trees become stressed and are more susceptible to additional problems and continuing decline.

Since the psyllids discovery in 1998 the Stanford Grounds Department has instituted a weekly pest monitoring program. A series of traps were placed within Eucalyptus trees in three locations, Searsville Road between West Campus Drive and Oak Road, the Auxiliary library, and the Grounds Corporation Yard. The traps are changed weekly. The traps are round plastic lids with a layer of STP as the sticky adherent to trap the adult psyllids. The traps are attached to a permanent yellow backing placed in the tree on a pole or on a stake. The collected traps are sent to the Center for Biological Control at the University of California at Berkeley. Dr. Donald Dahlsten and his staff at the center have been working to control the psyllid throughout California. The number of males and females on the trap are counted and entered into the Center's database.

A beneficial insect from Australia, a parasitic wasp was collected by Dr. Dahlsten and brought back to California. In the summer of 2000, after a year of strict laboratory observation of the parasitic wasp, a group of the wasps were released in Southern California. Additional releases occurred after that. A small group of parasitoids were released at the Stanford Campus, Searsville Road site in the fall of 2000 in hopes of establishing a colony. No parasitoids have been observed since the release. The parasitoid is harmless to humans and other animals. It is a psyllid parasitoid only. As additional parasitoids become available they will be released in larger numbers at two or three of the most severely infested sites in California. As a result of these releases we hope to see colonies of the beneficials established throughout all infested areas. There are a number of general insect predators that have been observed feeding on the psyllid at sites throughout California. For a list of the predators and additional information check the Red Gum Lerp Psyllid website mentioned above.