August 7, 2009

Tiny pest leaves Eucalyptus trees inundated

They live in a lerp. They wreck paint jobs on cars. And they kill eucalyptus trees.

The Red Gum lerp psyllid, first found in Merced County in 1998, has established itself as a major pest for the tens of thousands of eucalyptus trees that dot the county.

"Lerp" is an Australian aboriginal word for the little white waxy cup that the psyllid nymph lives under. And it's that sticky little insect home that people find on the hoods of their cars this time of year.

But another little insect is trying hard to kill those pesky psyllids -- and it's gotten a good start on helping save the aromatic trees.

David Robinson, agricultural commissioner for Merced County, said that the psyllids came from Australia, just like the trees they love to munch on.

But those trees came in the 1850s, when gold miners looking for shade in an almost treeless San Joaquin Valley started planting the fast-growing plants. For more than 100 years, eucalyptus trees had no insect pests and spread throughout the state. They grew fast, provided wood for burning and were drought-resistant.

Then the bugs came.

"They found the psyllids in Los Angeles in 1998, and that's when they started looking for a bug to help control it," Robinson said.

The result was a tiny parasitic wasp introduced from Australia to stop the psyllids, which can completely defoliate a tree in one season.

Robinson said the county started releasing the tiny wasps in November of 2001. They only parasitize the psyllid, and it's stingless -- so small it can sit on the head of a pen.

The psyllids make a cone-shaped little hut, the lerp, that they stay under when they are immature larvae. The wasp lays its eggs inside those immature psyllids, then newborn wasps eat the psyllid larvae.

The adult psyllids are green and small and can jump and fly. Both the larvae and the adult psyllids damage the trees.

After the 2001 release of the wasps, Robinson said, within eight months the wasp had established itself all the way from Le Grand to Delhi and was doing an effective job.

So why are so many eucalyptus trees filled this summer with those pesky, sticky white lerps that stick to everything they touch, not to mention killing the trees they're found in?

"During drought times, like we are in, the trees become stressed and more susceptible to insects like the psyllids," Robinson said.

When the pest was first found in California, Donald Dalhten, a professor of environmental science at the University of California, Berkeley, worked hard to find a natural pest of the pesky bugs. He found it in the little wasp that's been released throughout the state.

Dalhsten said that although eucalyptus trees are tough, they can't be defoliated continuously and live.

Because drought stresses eucalyptus trees, Robinson said people who want to help their trees weather the pest need to give the big trees some help.

"We advise that at least once a month to do a deep watering of the tree," Robinson said, adding that a drought-stressed tree is more susceptible to damage from the little bugs.

With a little bit of care from people and a tiny wasp, the big native-Australian trees that dot the countryside in Merced County can survive the attack of the psyllid.

"These trees are good habitat for hawks and other birds," Robinson said. "The government has done what it can to help the trees by releasing the wasps. Getting water to the trees will help even more."

Reporter Carol Reiter can be reached at (209) 385-2486 or

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