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Researchers Find Wasp Can Control
Spoted Gum Psyllid

 

News from
University of California-Davis

By UC Davis Staff
April 24, 2006

Anaheim is home to “the happiest place on earth,” and residents can continue to be in a jovial mood because two research scientists have found a tiny wasp that can control the spotted gum psyllid from attacking eucalyptus trees in southern California.

In August 2000, two psyllid species were discovered on lemon-scented gum and spotted gum trees in the Anaheim area. One is the spotted gum psyllid, a lerp psyllid, and another is the lemon gum psyllid. The insects cause leaf damage and drop which can stress trees and make them susceptible to fatal attack by other insects. Psyllids suck sap from leaves and produce a sticky substance called honeydew, which drops to the ground on cars and sidewalks.

The lerps vary in size, depending on the age of the larva. The larvae are yellow, or yellow and brown. Adults are 3 mm long, slender, and green. The small insects are native to Australia, and are another example of new exotic pests becoming established in California.

With three-year funding from the University of California Exotic/Invasive Pests and Diseases Research Program (UC EDRP), Tim Paine, entomologist from UC Riverside, and Kent Daane, UC Cooperative Extension specialist at UC Berkeley, performed studies to determine the pests’ seasonal distribution and abundance to see how to control the pests.

The researchers monitored the pests in Riverside, San Diego, and Orange counties. They found that psyllid populations in these areas generally have two high periods annually, in late spring and early summer and fall.

Daane and Paine used parasitoids previously collected by Don Dahlsten, formerly of UC Berkeley, on an exploration trip to Brisbane, Australia. Parasitoids are insects that lay eggs inside the bodies of other living insects. The hatched newborns feed off the bodies, eventually killing them. About 580 mummified psyllids were shipped to UC Berkeley and more than 300 adult parasitoids were reared in quarantine. After testing various species, one parasitoid, Psyllaephagus nr. Sp. hirtus, was found to be effective at controlling the spotted gum psyllid without destroying other beneficial species.

“Developing a biological control program may be the only effective long-term management for the spotted gym psyllid in California because there aren’t any selective insecticides that kill only psyllids,” says Paine. “Also, it’s difficult to spray large urban trees without pesticide drift.”

Some cultural control methods to deter the spotted gum psyllid are to apply water beneath the outer canopy of trees, but not near the trunks. Avoid frequent, shallow watering that is often used for lawns. Irrigate eucalyptus infrequently, but with sufficient amounts so that the water penetrates deeply into the soil. Water trees slowly through drip emitters that run continuously for several days. Also, avoid fertilizing eucalyptus. Use slow-release nutrient formulations if other plants near the drip line of eucalyptus trees require fertilization.

“If this biological control program is successful, it will significantly reduce the pesticide load in the environment and monetary costs in communities with high psyllid populations,” adds Paine.

The research duo’s discovery of what time of year the pest peaks will help them to time releases of the parasitoid in a statewide biological control program against the spotted gum psyllid. They have received another three-year grant from the UC EDRP to implement their program.

The UC EDRP targets research on exotic pests and diseases in California. The program aims not only to improve our knowledge and management of pests that are already here, but also to reduce the potential impact of those pests and diseases that pose a threat to the state. The program is collaboration between the UC Statewide IPM Program and the UC Riverside Center for Invasive Species Research.