Wasp Launched in War Against Ash Whitefly

Scientists launched the first attack in a biological war against the ash whitefly Friday when they released 60 tiny parasitic wasps in a San Fernando Valley park.

Perched atop ladders in Encino’s Balboa Sports Center, researchers reached into nylon mesh bags that had been wrapped around branches of two infested trees and uncorked several narrow, inch-long vials containing the predators.

“We’ve just taken a small step on a long journey,” said Los Angeles County Agricultural Commissioner Leon Spaugy.

Scientists are hoping for marked progress by 1991, but they say it will take up to five years to bring the whitefly under control.

The gold and black wasps, imported from Israel, look like dust specks and are about half the size of a pinhead.

The wasps do not sting humans. They can multiply only by laying their eggs within immature whiteflies. As the eggs develop, the growing wasps consume their host from the inside out, said Larry Bezark, a pest management specialist with the state Department of Food and Agriculture.

The whitefly has invaded trees from the Mexican border to Sacramento since it was first discovered at a Van Nuys fruit stand 14 months ago. Researchers fear that the pest, accidentally imported from Europe or the Middle East, could spread through much of California by next year because it has no natural enemies here.

“This is very serious,” UC Riverside entomologist Tom Bellows said as he stood beneath a tree infested with tens of thousands of whiteflies. “This is one of the most serious infestations of a foreign insect in the last 10 years.”

Friday’s release, coordinated by scientists at the UC Riverside and the Department of Food and Agriculture, is the first in a series of test releases of the tiny wasps planned this month in Los Angeles, Orange, Riverside, San Bernardino and San Diego counties.

The wasps will breed inside the mesh bags, enabling scientists to monitor their progress. In all, 300 of the wasps will be deployed this fall, with as many as 10,000 or more scheduled for release in the spring of 1990.

The test releases will help scientists determine if the wasp can survive the California winter outside the laboratory. Researchers are optimistic, noting that the wasps thrive under similar climatic conditions elsewhere. Entomologists will also be testing wasps imported from Italy, where the insect helps control the whitefly naturally.

The white-winged fly sucks vital juices from leaves, weakening and eventually defoliating trees. Ash and pear trees are its most common victims, but loquat, pomegranate, citrus, toyon and others are also at risk.

Pesticides have generally been unsuccessful for several reasons. Chemicals have a difficult time penetrating the waxy coat of the whitefly, and their eggs are hard to reach because they are laid on the underside of leaves, Bellows said.

The entomologist said the sheer number of whiteflies, which he estimated in the billions in the Los Angeles Basin, make the use of pesticides impractical and undesirable.

Although damage thus far has primarily been confined to shade trees and back-yard fruit trees, officials warn that the non-native pest poses a severe threat to the state’s nursery and citrus industries.

“There is a great potential for loss,” Bellows said.

Since the whitefly sucks more juice from plants than it can use, it leaves a sticky ooze in its wake that discolors fruit, stains patio furniture and ruins automobile paint. Residents throughout the Los Angeles Basin have complained that the swarming pests, which stick to hair and clothing, have ruined outdoor activities.