Imported Beetle Joins the Fray Against Ash Whitefly Infestation

Scientists waging a biological war against the pesky ash whitefly have deployed a new soldier in the fight--a tiny gold-and-brown beetle imported from Israel.

Small swarms of the so-called ladybird beetles have been released over the last three weeks in Granada Hills, Gardena and Oceanside. Entomologists predict that the eighth-inch-long beetle--which poses no threat to humans--will reduce whitefly populations by eating juvenile flies that attach themselves to the underside of tree leaves.

Meanwhile, researchers said thousands of stingless, parasitic wasps released earlier this year to prey on the whitefly appear to be doing their job.

UC Riverside entomologists do not yet have precise data on the wasps’ effectiveness, but they have observed the predatory insect reproducing and attacking the pinhead-sized whitefly in five Southern California counties.

“We’re very happy with the results,” entomologist Tim Paine said. A colleague, Tom Bellows, added that “the wasp appears to be a highly effective natural enemy” of the bothersome whitefly.

First discovered in Van Nuys two years ago, the ash whitefly has spread rapidly throughout California, infesting 20 counties from the Mexican border north to Sacramento.

The white-winged pest sucks the juice out of leaves and can defoliate entire trees. In the process, the bugs produce a sticky excretion that coats cars, patio furniture and sidewalks.

So far, the insect has mostly bothered urban dwellers and nursery owners, munching on ornamental trees. But entomologists note that the fly is known to attack fruit trees, raising concerns about its threat to the state’s agriculture industry.

Imported by accident from Europe, Africa or Asia, the whitefly has no natural predators in California. Pesticides provide only temporary relief, with new swarms of whiteflies reinfesting trees shortly after they are sprayed.

Consequently, entomologists agreed that biological warfare was the only way to stop the pest. The speck-sized, stingless wasps were imported from Italy and Israel and are being mass-raised by the California Department of Agriculture.

Large releases of the wasps began earlier this year and were made in 18 cities in Los Angeles, Riverside, San Bernardino, Orange and San Diego counties. In recent weeks, researchers returned to the field to determine how their troops were faring. What they found was encouraging.

The wasp attacks the whitefly by laying its eggs inside the whitefly nymph. Like a scene from a horror movie, the parasite’s egg then develops into a wasp, which eats its whitefly host from the inside out.

“In some of our research sites, if you pick up the leaves and look at the whitefly pupae, you’ll see that tremendous numbers of them show evidence of a parasite emerging rather than an adult whitefly,” Paine said. “The hole the whitefly makes when it comes out is very different than the hole the parasite makes, so we know when we’ve got success.”

Paine added that the observations were made in climates as different as the coast and the desert.

The ladybird beetles were released over the last two weeks at three sites. Further beetle releases are planned as entomologists continue mass-rearing the insects.

Paine said it will be sometime in the fall before researchers have a solid grasp of just how effective the predators have been in reducing the whitefly population.

Meanwhile, the entomologists hope to import still more whitefly enemies--another wasp from England that might be useful in the cooler climates of Northern California, and a parasitic fly from Israel.