Pest, Not Pesticide, May Be Solution to Sticky Problem

Thousands of tiny wasps from Australia will be released this month in Orange County and throughout California to prey on another insect that is literally bleeding the state’s eucalyptus trees, some of them to death.

Local officials and tree lovers are hoping the metallic-green wasps, each about the size of a rice grain, will slow the red gum lerp psyllid.

This tiny insect, also from Australia, was discovered in California in 1998 and has quickly worked its way throughout the state, ravaging eucalyptus trees.

In Orange County, “it has caused considerable defoliation of eucalyptus trees and also created sticky messes,” said Rick LeFeuvre, the county’s agricultural commissioner. “We prefer that the lerps not be here.”

Psyllids feed on eucalyptus tree fluids and leave a sticky substance on leaves that entomologists call “honeydew.” They also create “lerps,” minuscule domes of crystallized honeydew, on leaves to protect their young.

All of this tends to cause leaves to drop to the ground, where they stain sidewalks, plug up pool filters and fill storm drains. Eventually, the tree may die.

Scientists hoping to combat the psyllid without insecticides went to the psyllid’s homeland to find a natural predator. A species of wasp about which researchers know very little may be the answer, said Donald Dahlsten, an entomology professor at UC Berkeley.

The female of the wasp species, which has not yet been named, can penetrate a lerp, paralyze the immature psyllid, or nymph, and lay eggs inside its body, thereby killing the young psyllid, Dahlsten said. After hatching, each wasp larva chews its way out of the body and escapes the lerp to begin the cycle again. Dahlsten said the wasps pose no threat to humans or agriculture.

“It’s a wonderful, wonderful solution,” LeFeuvre said. “It helps reduce pesticide use. It’s a win-win for everybody.”

Local Release Site Not Yet Determined

Dahlsten hopes to release the wasps at a handful of sites around the state in the next one to three weeks. While some locations have been chosen in Los Angeles County, scientists have not yet determined where in Orange County the wasps will be let loose.

The release, which has received state and federal permits, is funded by the University of California’s College of Natural Resources at Berkeley and the Statewide Integrated Pest Management Program.

Though the success of the wasp release is uncertain, Dahlsten hopes the insects will multiply and quickly spread throughout the state, as did wasps of a different species that he released in 1992. The earlier wasp release successfully slowed the spread of the blue gum psyllid, which also damages eucalyptus trees.

Dahlsten hopes to create a balance of wasps and psyllids, with enough of the pests remaining to keep a population of wasps alive and ready to stem future infestations.

“In an ideal situation, we don’t want to eradicate the psyllids, because the psyllids undoubtedly will get back here,” he said.

Eucalyptus trees are native to Australia and were introduced to California in 1859. Red gum psyllids, first identified in Australia in the 1960s, were first discovered in California in El Monte in 1998. They have spread into San Diego and the Inland Empire and north to the Bay Area and beyond.

LeFeuvre said that although no countywide damage estimate exists, several cities have had significant problems.

In Dana Point, 1,850 of the city’s 2,500 eucalyptus trees have been infected by the insect since last year, said Gary Groshon, the city’s parks manager. Most of the infected trees are at Dana Point Harbor and Doheny State Park.

In San Juan Capistrano, city officials have begun using a pesticide to save infected eucalyptus trees. About 15% of the trees in the city have been infected by the insect.

Jack Galaviz, San Juan Capistrano’s public works manager, said the insects would eventually kill the trees. After infestation by red gum lerp psyllids, trees become prone to attacks by other insects, such as borer beetles, and diseases, such as root rot, that can kill them.

About a third of the eucalyptus trees at the Arboretum of Los Angeles County in Arcadia, which has the largest eucalyptus collection outside Australia, are infected with psyllids.

Last year, the city of Los Angeles bombarded parks and some streets with millions of ladybugs, a natural predator of psyllids, to little avail.

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Fighting a Tree-Sucking Pest

UC Berkeley scientists are studying a tiny wasp parasite they hope will eradicate an insect pest that weakens eucalyptus trees by sucking the sap out of its leaves and by blocking photosynthesis.

Red Gum Lerp Psyllid

1. Tiny wasp punctures sticky lerp (protective coating)

2. Lays eggs inside psyllid nymph

3. Wasps larvae hatch, eat their way out of dead nymph

Source: UC Berkeley Center for Biological Control