BACKGROUND

First spotted in Van Nuys in 1988, the ash whitefly has spread north to Sacramento and south to the U.S.-Mexico border. The pinhead-sized insect sucks the juice from the leaves of shade and ornamental trees, often defoliating them, and excretes a sticky sap that coats cars, patios and sidewalks. Pesticides are ineffective because of the whitefly’s huge numbers, and the insect has no natural predators in California. So scientists have released two imported enemies--a stingless wasp and a ladybird beetle--to prey on the irksome pest.