State trees might be saved by wasp, CNR researcher discovers

September 06, 1999
By Kathleen Scalise, UC Berkeley Public Affairs

BERKELEY--Relief may be in sight for California eucalyptus trees hard hit by a new insect pest. A tiny wasp just discovered by a scientist at the University of California, Berkeley, may be the cure for the damaged trees.

Under attack from the redgum lerp psyllid, trees lose their leaves and produce a sticky honeydew that dirties cars, buildings and sidewalks. The psyllid has caused much concern in the state since first found in Los Angeles County in June 1998.

'People are afraid they are going to lose their trees,' said Donald Dahlsten, a professor of environmental science, policy and management and biological control in the College of Natural Resources.

The newly discovered wasps might control the psyllids spreading infestation by laying its eggs in the insect and killing it.

This psyllid infestation has now been reported in 30 California counties. In the Bay Area, trees at Stanford University, Ardenwood Park in Fremont and parts of Walnut Creek have suffered particular damage. In Southern California, those hardest hit include the Los Angeles suburbs of North Hollywood and Valley Village and the cities of Torrance, Riverside and Palos Verdes.

The problem psyllid is Glycaspis brimblecombei, a small, flying insect that feeds on plant juices. It has been collected on about 16 different varieties of eucalyptus in California, but is causing the most trouble on redgum, Eucalyptus camaldulensis, a common ornamental eucalyptus tree species.

'These are tough trees,' said Dahlsten, 'but the question is how many times they can be defoliated before they die.'

Dahlsten returned from Australia on Sept. 1 with two shipments of the new parasitic wasps. Each the size of a grain of pepper, the wasps are so small it's hard to believe they could save gigantic trees. They skitter around their cages at UC Berkeley's insect quarantine facility like minuscule ants and have not been officially classified. But they may include as many as three species of Psyllaephagus that feed on the California's problem psyllid pest, the first lerp psyllid ever found in the United States.

'We don't have lerps here, so their appearance caused quite a stir,' said Dahlsten.

'Lerp' is an Australian aboriginal word for the small sugary wax cup the psyllid nymph or juvenile stage produces to cover and protect itself. How the insect got to California is unknown, said Dahlsten, but it has spread rapidly.

'Oh, boy, it's really not looking good at all,' said horticultural analyst Carol Sweetapple of Stanford University, which has one of the worst infestations in the Bay Area.

Stanford red gums trees are defoliating for the second year in a row, she said, and some of them have lost 85 percent of their leaves. Sweetapple doesn't know if the trees do enough photosynthesis to survive with such small canopies.

'For us, the eucalyptus are very valuable, both for historical reasons -- we have a fabulous collection -- and for the ambiance,' she said. 'Imagine the hills behind Berkeley barren. That's what it would be like for us to lose these trees.'

It could take a year or more before it's known whether the wasps will be released in California. Dahlsten is hopeful they will prove safe. He believes the wasps feed only on lerp psyllids, but says it remains to be proven that they won't pose a danger to other insects.

Already, Dahlsten has requests from places that want to be at the top of the release list.

'Everybody wants the parasites,' said Dahlsten. 'Especially people in Los Angeles have been pressing me, saying, 'we need to release right away,' but I won't do this. We need to make sure it's safe. '

Dahlsten is credited with saving the state's foliage industry in 1991-93 from a disaster on a species of eucalyptus used in the flower trade. It would have cost California's eucalyptus growers millions of dollars to control the problem year after year had Dahlsten not discovered an insect cure.

Not everyone thinks scientists should bother trying to save eucalyptus in California. The trees were brought in from Australia in the 1850s and planted extensively in the early 1900s by timber speculators who mistakenly thought the wood would be valuable. Only later did they realize it had a tendency to warp, shrink and check, said Dahlsten.

But the eucalyptus tree remains a dominant feature of the California landscape.

'There are anti-eucalyptus and anti-exotics people who could care less if we lost them all,' he said. 'But other people who have these trees will do anything to save them, including dousing them with pesticides.' It costs $500 to inject each tree with pesticides, and Dahlsten is not sure it helps.

He said he wishes eucalyptus had never become so popular in California, but to get rid of them now requires a systematic removal and replacement plan.

Stanford University, for one, doesn't like that idea at all. So this fall, Stanford and other eucalyptus owners around the state will be cheering on the Berkeley solution.

For more information please go to Dr. Dahlsten's Red Gum Lerp Psyllid - Main Page.