Wasps Losing a War

Maybe they’re just not in the mood.

There’s a puzzling snag in an ambitious plan to use Australian wasps to kill off a rapidly spreading bug that is literally sucking the life out of eucalyptus trees across California: The wasps aren’t reproducing enough.

“The males of the species are kind of loose cannons,” said Pat Madsen, an arborist for the city of Tustin, where more than 1,500 trees have been infested by the red gum lerp psyllid.

“They’re not taking care of the needs of the females. That’s the best way I can put it.”

Scientists at two state-run labs have tried for more than a year to get the wasps, which are about the size of a rice grain, to breed by the tens of thousands. So far, they’ve managed to get just a fraction of the bugs they need, and are woefully short of female wasps, the ones that attack the psyllid.

“If we knew everything, we could have solved the problem a long time ago,” said Donald Dahlsten, who is in charge of the project at the Center for Biological Control at UC Berkeley. “But it’s tough.”

Dahlsten went to Australia to collect the wasps, one of the psyllid’s natural predators, after the psyllid somehow made its way to California in 1998. Now, he’s trying everything to get the wasps to mate.

He has experimented with the lighting in the laboratory ecosystems built for them. He has fiddled with the temperature and humidity. He has enticed them with tiny forests built in cages, and isolated them in individual vials.

Nothing has worked.

“A lot of times, programs like this can take two or three years” to succeed, Dahlsten said. “But there’s a lot of anxiety out there because the trees are looking so bad.”

At stake are hundreds of thousands of red gum eucalyptus, a native of Australia that was introduced to California in the 1850s. About 33,000 of them are in the south Orange County city of Lake Forest, which has been particularly hard hit by the psyllid.

In the early 1900s, an entrepreneur planted 400 acres of eucalyptus in south Orange County in an attempt to cash in on a lumber shortage. The venture failed. But half a century later, the trees caught the imagination of a developer who built a master-planned community amid them.

Now, as many as a third of Lake Forest’s red gum eucalyptus are infested.

On a cul-de-sac named Meadowwood, there is already plenty of dead wood.

“This is dead. That’s dead,” said resident Ron Ayres, pointing to the eucalyptus in his frontyard. “Most everything in here is dead. . . . My wife cries whenever she thinks of those trees coming out.”

Psyllids began feeding on Ayres’ eucalyptus trees two summers ago, sucking the fluid from the long, finger-like leaves, then laying their eggs and covering them with a sticky wax tent.

One of the first signs of the trouble the insects could create appeared when those leaves died and hit the ground. “They stuck to your shoes, stuck to your carpet. You had to wash your car every day,” Ayres said. “The stuff actually eats the paint.”

Across the street, Helen Walsh considers the consequences. She has already cut down four dead trees; of the 31 she has left, only six may survive. To remove and replace them all will probably cost more than $10,000.

Her front lawn is a eucalyptus graveyard, a collection of poles stuck in the ground, their leaves gone.

“It’s awful, just awful,” Walsh said. “One of the reasons we moved here was because of the trees. It’s very depressing.”

Chemical treatments aren’t a long-term solution, and they’re expensive. But she heard of the wasps that attack the psyllids, and when she saw some wasps last year, she had reason for hope.

But they weren’t the right wasps.

Because of the breeding problem, scientists have been able to release the wasps at only 21 sites statewide--and Lake Forest isn’t one of them.

Though the releases have been limited, the results are promising, Dahlsten said. At two areas--North Hollywood and Redwood City--there is evidence that the wasps are generating offspring. The hope is that those wild wasps will begin reproducing more, making up for what’s not happening in the lab.

If that doesn’t work, Dahlsten will probably return to Australia to look for other natural enemies of the psyllid.

“We’ve never had an insect that has moved so fast through so many trees,” said John Kabashima, an environmental horticulture advisor with the University of California Cooperative Extension. “This coming season is a critical season for us.”

(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

Battle Plan

Scientists are trying to get a tiny wasp to reproduce in the laboratory, in hopes that it can eradicate the lerp psyllid, an insect that weakens red gum eucalyptus trees. How the wasp kills the psyllid:

1. Wasp punctures sticky lerp (protective coating)

2. Lays eggs inside psyllid nymph, eventually killing it

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

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Source: UC Berkeley Center for Biological Control