State Still Says Wasps Are Best Whitefly Weapon Despite Test

Despite an ambiguous showing in an Encino park, state agricultural experts have not lost faith in the tiny Israeli wasp they want to use as a weapon in the war against the ash whitefly.

Over the past two months, researchers pitted the wasps against whiteflies at the Balboa Sports Center in Encino, yielding inconclusive results. In a more closely monitored test in Riverside, researchers said, the wasps reproduced and fed on the whiteflies, which damage fruit, shade trees and shrubbery.

The whiteflies have spread throughout California. A state official said Wednesday that wide release of the wasps, which are harmless to humans, could begin this spring.

Ash whiteflies weaken and eventually defoliate trees by sucking vital juices from their leaves. The insects also exude a sticky substance that can damage patio furniture and automobile paint.

“We’re more than encouraged,” said Kathy Brunetti, program supervisor for the California Department of Food and Agriculture. “We’re convinced that bio-control will be our weapon against the whitefly.”

Bio-control refers to the use of natural predators to kill an undesirable insect, instead of chemical methods. To combat the whitefly, the state has begun breeding tiny Encarsia wasps, imported from Israel, in Riverside. “We are anticipating right now to have a large-scale release sometime this spring,” Brunetti said.

Since it was discovered about two years ago at a Van Nuys fruit stand, the ash whitefly has invaded trees from the Mexican border to Sacramento. The insect, normally found in Europe and the Middle East, has spread quickly because it has no natural enemies in California.

“I think of it as the Pilgrim Fathers Syndrome,” Brunetti said. “The pilgrims came here and left their enemies behind in Europe. Now we’re going back there to bring their enemies over here.”

She said a spring release of the wasps in Southern California probably will be followed by a late-summer release in the northern portion of the state.

With funding and staff help from government agencies and grower associations, Tom Bellows, an entomologist at UC Riverside, has been trying to determine whether the imported wasps will reproduce in Southern California’s climate and attack the whitefly. In November, Bellows released about 60 of the parasitic wasps at the Balboa Sports Center.

But when he checked the experiment early this month, he could not tell whether the wasps had multiplied and fed on whiteflies. He said the trees that might have provided such evidence had lost their leaves because of cold weather. However, a similar test closer to his laboratory provided more promising results.

“We put 123 wasps in Riverside,” Bellows said. “Seven or eight weeks later we found evidence that reproduction had occurred and the wasps were successfully established. We found 97 dead whiteflies that had been killed by the wasps. That’s very encouraging for that size of an experiment.”

He said similar experiments are under way in San Bernardino, San Diego and Orange counties and include the use of wasps imported from Italy. Bellows said he plans to test still other wasps and a breed of beetle to find the most effective whitefly predator.

The imported wasps lay eggs within immature whiteflies, and the developing wasps consume their hosts from within, researchers said.

On Jan. 16, state Assemblyman Terry B. Friedman (D-Los Angeles) introduced a bill that would provide $2 million for control of the whitefly over the next five years, using only natural predators. “We don’t think there will be any opposition at all,” said Karin Caves, a spokeswoman for the legislator.

Treatment of the Mediterranean fruit fly with the chemical malathion has met with increasing opposition from politicians and community activists in recent months.