Wasps to Be Warriors in Fight Against Ash Whitefly : Pest: Agricultural officials plan to release the stingless insects in a biological battle against the annoying bugs, which are immune to pesticides.

Biological war has been declared against a fly that is ravaging trees in Ventura County, a state agricultural official said Friday.

Agricultural officials are planning to release another bug in July as the latest weapon in the assault against the destructive ash whitefly, said Veda Federighi, a spokeswoman for the pest management division of the state Department of Food and Agriculture.

About 250 tiny stingless wasps, which are not dangerous to humans but destroy whiteflies, will be released at each of four locations in the county, Federighi said. Actual release sites have yet to be determined, she said.

The ash whitefly is a nuisance to homeowners whose shade trees are attacked by the pesky insect. It also poses a threat to farmers in the 17 counties where it has been found.

Because it is immune to pesticides and has no natural predators, it is only a matter of time before the ash whitefly threatens commercial crops, including citrus fruits, apples, pears and pomegranates, agricultural officials said.

Swarms of the predatory wasps have already been deployed successfully elsewhere in Southern California during experiments conducted by UC Riverside researchers.

Scientists had to go to Italy and Israel to find the insects that are hostile to the ash whitefly. The species to be used in Ventura County is from Israel, Federighi said.

Use of biological rather than chemical controls on the ash whitefly is new to Ventura County. The insect has been spotted on trees in the eastern part of the county, primarily Simi Valley and Thousand Oaks.

The ash whitefly was first spotted in 1988 and “spread like wildfire” last summer, Ventura County Deputy Agricultural Commissioner Ken Weiss said. Experts say that using a parasitic enemy of the whitefly before summer starts may slow the fly’s spread.

“It’s the only control at this point that seems to have any prospect of diminishing this pest,” Weiss said. “Insecticides don’t seem to do a great deal.”

Weiss said it could take more than one season to establish a substantial army of wasps to control the ash whitefly.

The tiny whitefly is typically found on the underside of leaves on shade and ornamental trees. Left unchecked, the insect eventually kills all the leaves on a tree.

What makes the ash whitefly so irksome to urban dwellers is the sticky fluid it produces when it sucks the sap out of trees. The fluid coats cars, sidewalks and patio furniture.

Jim Spalding, a Simi Valley resident who discovered the pest on his ash trees last year, said he was annoyed to find hundreds of tiny flies in the air and patio furniture covered with a sticky mess.

“You’d shake the leaves and it’d look like a cloud,” Spalding said. “There were little bitty whiteflies everywhere.”

Spalding said it was so difficult to eradicate the fly that he was forced to cut down his 20-foot-tall trees.

Scientists say the release of insects hostile to the ash whitefly will prevent Ventura County homeowners from taking an ax to their trees.

Previous releases of parasites that attack the ash whitefly “gave us a lot of optimism about the success of the wasps,” said Janet White, a spokeswoman for UC Riverside, where the black-and-gold wasps are reproduced in laboratories. It will take about five years for researchers to evaluate the use of beneficial insects against the ash whitefly, she said.

In the meantime, the use of wasps to control the ash whitefly may prove less costly and safer than chemical pesticides, White said.

“The payoff is great because finally you have a control system without the use of pesticides, and it’s self-sustaining,” White said.