State, San Diego County Team to Swat Whitefly

California and San Diego County agricultural officials are attempting to deliver a one-two punch to the giant whitefly, a tiny pest with a big appetite for hibiscus and citrus trees.

First spotted on hibiscus plants in Mission Bay five years ago, the giant whitefly has spread to urban areas and now also exists in Orange and Los Angeles counties. In addition to hibiscus, it attacks a common ornamental shrub called xylosma, bird of paradise plants and backyard citrus and avocado trees.

Although it hasn’t yet reached commercial crop fields, the giant whitefly is harming nurseries and “it definitely threatens farms,” said David Kellum, San Diego County’s entomologist.

Hoping to nip this bug in the bud, state and county officials have joined with a Leucadia nursery and an Escondido insectary to test the production and use of natural enemies--nonstinging wasps and ladybird beetles. The experiment is an example of what entomologists call “classical biological control,” in which natural enemies, usually from abroad, are reunited with pests that have been accidentally introduced into a region.

California began delving into biocontrol in the mid-1880s, when the Vidalia beetle threatened to wipe out the state’s citrus industry. The importation from Australia of two natural enemies--a fly and a beetle--saved the fruit trees.

With the invention of modern pesticides in the 1930s, biological control faded in importance, but it is staging a comeback as growers seek to limit the ill effects of chemicals.

In addition to other programs, environmental research scientists and entomologists in California are participating in a large national project to control the silverleaf whitefly, which affects a range of fruits and vegetables, notably melons, cotton and broccoli.

“We’re just starting to get some substantial results [indicating that we have] some pretty good parasites,” said Charles H. Pickett, an associate environmental research scientist with the California Department of Food and Agriculture.

Pickett said California has enjoyed a “smash success” in controlling the ash whitefly, a European pest that had no natural enemies here and was therefore free to feast on the state’s popular ash and ornamental pear trees in the early 1990s. Brought under control by a tiny stingless wasp, it now exists only “in very low numbers, and nobody has to spray,” said Mary Louise Flint, a UC extension entomologist.

Pickett hopes for similar success with the giant whitefly, which produces a waxy honeydew that protects it from chemicals applied by growers. At the San Diego Zoo, clusters of waxy threads from the pest are in evidence on 40 species of plants and can be seen floating through the air on breezy days.

“It creates a horrendous mess,” Pickett said.

Bing Went the Strings . . .

California cherries last month began crossing the border into Mexico for the first time since 1991. Elimination of a ban that Mexico imposed that year on U.S.-grown cherries because of pest concerns coincided with the U.S. Department of Agriculture’s recent decision to allow Mexican avocados into this country for the first time in eight decades.

Jim Culbertson, who manages a Lodi-based marketing order for four varieties of sweet cherries grown in the state, said there was “no formal linkage” between the two disputes. But he indicated that the avocado decision probably helped the cherry industry, the first to use the North American Free Trade Agreement dispute- resolution process to settle a conflict.

Culbertson said it was hard to say how much in sales the lifting of the ban could mean to the state’s cherry growers, but it could be at least a few million dollars.

Cherries are grown in 10 Golden State counties, led by San Joaquin.

Martha Groves can be reached by e-mail at [email protected] or by fax at (213) 237-7837.

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Great White Pest

The giant whitefly--a pest afflicting hibiscus and other plants in San Diego, Los Angeles and Orange counties--is a giant among the 21 species of whitefly. Here are other tidbits about the insect:

* Latin name: Aeurodicus dugesii.

* Order: Homoptera, which also includes aphids and scale insects.

* Diet: Hibiscus, xylosma (a common evergreen shrub), bird of paradise and backyard avocado and citrus trees.

* Size: One-eighth to one-fourth inch long, three times bigger than the average whitefly.

* Natural enemies: Entedononecremnus krauteri (nonstinging wasps) and Delphastus catalinae (ladybird beetles).

* Native turf: Southern Mexico, Central America, southern tip of Baja California

Source: California Department of Food and Agriculture