Insect Pitted Against Insect to Save Trees
Thousands of tiny wasps from Australia will be released this month in Los Angeles 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 through the state, ravaging eucalyptus trees.
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 one, said Donald Dahlsten, an entomology professor at UC Berkeley.
The female of the wasp species, which has not yet been named, can penetrate lerps, paralyze the nymph and lay eggs inside its body and thereby kill 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,” said Rick LeFeuvre, Orange County’s agricultural commissioner. “It helps reduce pesticide use, it’s a win-win for everybody.”
Dahlsten hopes to release the wasps at a handful of sites around the state in the next one to three weeks--including several in Los Angeles County that already have monitoring traps.
“Probably a site in Woodland Hills and North Hollywood. One near Griffith Park. And one in Torrance,” Dahlsten said.
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 he released in 1992. The earlier wasp release successfully slowed 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. They have spread into San Diego, the Inland Empire and north to the Bay Area and beyond.
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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Times staff writer Annette Kondo contributed to this report.
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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 from leaves and by blocking photosynthesis.
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Source: UC Berkeley Center for Biological Control
