GOINGS ON

Since 1984, eucalyptus trees from the Bay Area to San Diego have been under assault from Phoracantha semipunctata --Australia’s eucalyptus longhorn borer. This voracious alien has no local enemies, resists pesticides and can kill a sapling in a summer; a mature tree in a year.

But researchers are battling back with help from Down Under: five species of Australian wasps that prey upon baby borers. The first of the wasps, Syngaster lepidus , was introduced about four years ago but was pretty much a washout; it just couldn’t adapt to life north of the equator. So UC Riverside entomologists enlisted more recruits from Australia’s insect armies, and over the past year, they have released four other wasp species in several parts of Southern California. To all these wasps, beetles are prime baby food. The female wasps of one species lay eggs that invade and inhabit the borer’s eggs; the others paralyze the beetle larvae, then lay eggs inside the moribund mass. As the wasps mature, they use the grub for grub.

Researchers are now waiting to see if the wasps can survive here--and if they work against the borer. “We won’t know how effective they’ll be for at least another year,” says UC Riverside entomologist Robert F. Luck.

In the meantime, females borers will continue to seek out eucalyptus trees, laying as many as 300 eggs on the shaggy bark from May to October. The eggs hatch within two weeks, and the larvae tunnel into the tree, eating vital tissue and gradually starving the tree. Healthy eucalyptus trees produce a thick sap that usually drowns the larvae, but the drought has weakened thousands of trees. No one knows how many trees P . semipunctata has destroyed, but the tally is easily in the thousands.

Until the wasps can control the borers, hydration is the best bet for beating the beetle. “The best protection is watering the trees through spring or summer months,” says Paul Pondella, owner of Tree King, a Los Angeles tree service. “Soaker hoses work best. The more water you can get to the tree, the better.”