Australian Beetles Threaten Catalina Eucalyptus

An aggressive Australian beetle that has destroyed hundreds of eucalyptus trees throughout Southern California has spread to Santa Catalina Island, where 90% of the non-indigenous trees are eucalyptus.

Catalina has “quite an infestation,” said Paul Rippens, senior deputy forester for the Los Angeles County Fire Department. During an inspection this week to see whether the pest had reached the island, Rippens said he found the insect in dozens of eucalyptus trees, which now must be destroyed.

The beetle presents a particular threat on Catalina Island, Rippens said. Nearly all of the trees that were planted on the island are eucalyptus, he said, and an irrigation method normally used to keep the insect away from healthy trees is impractical there because of a water shortage. In fact, the shortage is a major reason for the popularity of the tree, which normally survives on little water.

“Because water is so expensive on the island, few trees are watered,” Rippens said, except at Wrigley Memorial and Botanical Garden. As a result, he said, “Many of the trees are under a lot of stress, and get cracks in their bark. The beetle has the ability to pick out the weakest trees.”

The voracious beetle, known as the eucalyptus longhorn borer, was probably brought to the island more than a year ago, Rippens said, judging by the number of trees affected. He speculated that it came in a load of eucalyptus firewood.

The infestation is already widespread, according to Doug Propst, president of the Santa Catalina Island Conservancy, the agency that owns 86% of the rugged island. “I think they’re pretty much across the island, at the isthmus, at Two Harbors and here in Avalon,” he said. “We’re having a pretty dry year now, and that makes the trees even more susceptible.”

Several independent entomologists will examine the island’s eucalyptus trees this week, Propst said. Then, the conservancy will meet with forestry officials to decide how to attack the problem, he said.

The borer beetle, which is indigenous to Australia, was first found in Southern California in 1984, in wood that had been shipped from Australia to an El Toro lumberyard in Orange County.

The insect has since destroyed eucalyptus trees from San Diego County to Ventura County and into San Bernardino and Riverside counties, forestry officials said. Adult beetles can fly up to nine miles during migration, which occurs at night.

Some eucalyptus trees in the South Bay have undoubtedly been attacked by the beetle, officials said, but no figures for the area are available.

The insect--a brownish-black bug about 1 1/2 inches long with a coral-colored streak on its back--bores into the wood of drier eucalyptus trees and lays its eggs in the tree’s cambium layer, the area between the wood and the bark where growth occurs and where nutrients are transported. The larvae encircle the tree and starve it.

Rosser W. Garrison, an entomologist with the Los Angeles County agricultural commissioner’s office, said females can lay as many as 300 eggs in “water-stressed” trees whose barks and trunks are especially dry.

Healthier trees can produce enough sap to kill the beetle, Garrison said. Insecticides are “impractical and not really effective” in killing the hardy insect because the chemicals cannot penetrate wood, he said.

Once infected, a tree cannot be saved, Garrison said. Signs of infestation include a flat trail on the wood beneath the tree’s bark and half-inch-round holes in the bark from which adult beetles emerge. Infected trees should be cut down and burned immediately, or covered with tarp or plastic, if possible, until the insects die, he said. Wood from an infected tree should not be saved for firewood because the insect will continue to breed.

To protect healthy eucalyptus trees from infestation, forestry officials recommend irrigating the soil at the base of the tree with a trickling water hose over a 24-hour period every few weeks to increase the sap produced by the tree. Additional soil may be needed at the tree’s base to hold the water, and longer soaking may be necessary for trees in clay soil.

In Australia, the beetle is controlled by natural predators, including certain wasps and some other beetles, Garrison said. These predatory insects, however, are not found in Southern California.

Researchers at the University of California at Riverside are working on ways to control the pest and studying the merits of importing the predatory insects from Australia, he said.

The possibility that the borer beetle might destroy the entire eucalyptus population on Catalina Island or elsewhere in Southern California are “practically nil,” Garrison said.

“It will undoubtedly spread, “ he said. “The beetle will attack many eucalyptus trees, but those that are healthy will have no problem. It will not eradicate all eucalyptus trees.”