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An Australian insect is killing Southern California's eucalyptus.

An Australian insect is killing Southern California's eucalyptus

For 128 years, the eucalyptus reigned in California as, among other things, a pest-free tree. Then, in 1984, one of its Australian pests finally found its way to our shores, and it immediately went to work. It acts much faster here than it does in Australia because California lacks all the other creatures that keep the insect in check there.

The beetle is the eucalyptus longhorn borer or ELHB (Phoracantha semipunctata). First discovered in El Toro, just south of Irvine, in October 1984, it quickly migrated, killing eucalyptus trees in South Laguna. It inflicted heaviest damage in Lake Forest, where houses are built among what was once a eucalyptus forest. To date, it has been found along the coast from Long Beach to San Diego, inland from Van Nuys to Hemet. Unconfirmed reports note the beetle in Ventura, and experts fear that the pest will spread along the coast into northern California and into the Central Valley and perhaps Arizona in a few years. (It has been established in Hawaii since 1965.)

How it got to Southern California is anybody's guess: some speculate that larvae may have hitchhiked directly from Australia in lumber or in a wooden crate. The beetle spreads fastest by way of firewood shipments, but an adult beetle is a strong flier and can cover 9 miles on its own. It is also prolific: three generations are produced in a year.

The pictures on the opposite page show what the pest looks like at various stages of life and the damage it does to eucalyptus trees. Much of the damage goes on beneath the bark, and the adults fly only at night. As a result, the first signs you're likely to see are the adult-exit holes shown in the photograph at left.

From egg to adult beetle in 90 days

The beetle is active throughout the year, slowing down some in winter. During summer, its life cycle from egg to adult takes about 90 days. Overwintered and newly emerged adults lay eggs in spring. Larvae feed through summer, pupate, and emerge as adults in fall to lay more eggs.

Adults usually lay eggs near a wound such as the stub of a broken branch or on fresh-cut logs. In about two weeks, larvae hatch and begin feeding right away.

Nearly mature larvae chew channels up to three times wider than their heads. Near maturity, larvae bore telltale holes in the trunk 2 inches into the tree to form the pupal chamber. The adults emerge through those holes after about 20 days.

Symptoms to watch for

In addition to the pests themselves and their telltale holes and channeling, other signs tell of beetle trouble. A healthy eucalyptus responds to beetle attack (or any wound) by producing a resinous brown sap-like material called kino. It's one of the first symptoms of beetle attack you might see and is believed to be somewhat toxic to the borers. Stressed trees have a harder time producing this sap.

If a eucalyptus is simply suffering from drought or other physical privation, leaves turn brown and drop gradually; they don't brown all at once as they do from this beetle's work.

Which eucalypts get it and which don't

In Australia, this beetle is one of many insects that feed on eucalyptus wood. It rarely kills healthy trees there because it's held in check by a complex ecological balance. Here, the beetle is without natural enemies.

Whether any eucalyptus species is immune, resistant, or susceptible to beetle attack is not yet known. So far, researchers have noted that E. globulus and E. viminalis die quickly when attacked; E. blakelyi and E. cladocalyx protect themselves longer with heavy sap flow, even during drought. In Australia, virtually all species common here are attacked by the beetle.

What you can do

First, examine all eucalyptus firewood for the under-bark feeding galleries created by larvae. If you find any such wood, immediately burn or buy it--or cover it with a tightly closed tarp for at least six months.

Promptly remove a dead or dying tree. Bury (or cover with a tarp) logs cut from an infested tree. The burying or wrapping keeps would-be emerging adults trapped inside.

At present, no pesticide or biocontrol method eliminates the beetle. Specialists from UC Riverside recently studied the beetle and its enemies in Australia and plan to begin importing the most effective wasp parasites and beetle predator this fall; first releases are planned for next spring. How effective they will be or how fast they will work is unknown now.

Photo: Oval holes like these, going straight into the trunk, are obvious signs of infestation. They're where the adult beetles exit after pupating

Photo: Eggs, elongated like rice grains but much smaller, were laid on underside of bark that had lifted. Adult lays eggs at night; in two weeks, they hatch into tiny larvae

Photo: Creamy white larvae, about 3/4 inch long and about 45 days old, tunnel below bark to feed on nutrient-carrying sapwood. Bark was pulled back to reveal this pair

Photo: Adult beetle has distinctive markings. It hides under bark during the day; at night it flies, mates, lays eggs, sometimes feeds on flower pollen

Photo: Borer damage. Above, eucalyptus trunk with bark peeled shows meandering channels larvae chewed in sapwood (probably done by more than a dozen larvae). One horizontal channel, if long enough, can girdle and kill a tree. At left, typical overall result: entire branches dead with leaves still attached, in San Juan Capistrano
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Copyright 1986 Gale, Cengage Learning. All rights reserved.

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Title Annotation:eucalyptus longhorn borer
Date:Oct 1, 1986
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