Scientists hope parasitic wasps save trees

The Associated Press
Friday October 13, 2000

SHELDON — Scientists released about 100 flea-sized wasps Thursday in Sacramento County, hoping the Australian insects will seek their natural food source: a bug killing eucalyptus trees. 

The parasitoid wasp release is the eleventh in California, where the redgum lerp psyllid has infested at least 40 counties, said Don Dahlsten, a University of California, Berkeley, entomology professor. 

Trees in the Central Valley and along the coast are the most affected. 

Researchers say it is too early to tell if their plan is working; only one wasp has been reclaimed after a release. 

UC officials in Sacramento County said they had received about 130 requests for the wasp from homeowners whose eucalyptus trees serve as fences, wind guards and landscaping. 

The tree-saving program has its share of critics, who contend the eucalyptus tree is a nonnative plant that should not be saved, especially not at the risk of introducing another nonnative species to protect it. 

The long-term consequences of introducing the wasp are unclear, said Jacob Sigg, president of the California Native Plant Society. 

“In principal most people agree it’s OK to import exotic organisms to control an exotic weed,” Sigg said. “When we go beyond that and there is a predator of a predator of an exotic plant” that needs to be debated. 

Several organizations have pushed for the tree’s eradication. Dahlsten said he frequently gets angry letters from people opposed to the introduction of new species. 

“I hope I’m doing the right thing,” he said, holding a test tube with the tiny, non-stinging wasps inside. “I’ve been called irresponsible and have gotten hate mail but if we don’t chose this solution, these tree owners will spend thousands on chemical pesticides that won’t work in the end but will ruin our water, our soil.” 

Dahlsten collected the wasps from Australia, where native eucalyptus trees have thrived despite the redgum lerp psyllid because the psyllids are threatened by the wasps. 

The psyllids feast on eucalyptus trees by sucking sugary sap from the tree leaves, robbing the tree’s roots of needed nutrients, said Ingels. 

White sacks on the tree leaves conceal immature psyllids growing to maturity. 

The wasps live and plant their eggs in the psyllids. Breeding the wasps has been difficult because they only live six weeks and need the psyllids to reproduce. 

“We are 99.9 percent sure this is not going to affect other insects in the area, because it has been tested on similar insects,” said Chuck Ingels, a UC farm adviser in Sacramento County. 

On the Net: 

For more on the wasp release see: http://www.cnr.berkeley.edu/biocon/dahlsten/rglp/index.htm 

Find the California Native Plant Society at www.cnps.org