Western Tussock Moth

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Western tussock moth has one generation a year. Overwintered eggs hatch about the time the spring growth flush is expanding. Larvae of the western tussock moth are distinctive: young larvae are black with long bristles; maturing larvae have numerous red and yellow spots and four median dorsal tufts of light gray hair. Mature larvae spin their cocoons and pupate mainly on scaffold branches and trunks.

Adults emerge from late April through July and, after mating, wingless females lay 125 to 300 eggs each in a single egg mass—usually on the empty pupal case. Adult males are generally brownish and have wings that, when at rest and viewed from above, form a roughly triangular outline. The topsides of the male's forewings are darker with grayish areas and have two irregular darker markings that cross at one-third and two-thirds of their length.

Western tussock moth infestations are occasionally a problem in Southern California and in foothill orchards in the San Joaquin Valley. A heavy infestation of this pest may destroy all new spring growth. The larva may also eat into newly set or young fruit. The damage is similar to that of katydids, grasshoppers, and citrus cutworm.

Manage western tussock moth by monitoring in spring and applying an insecticide when necessary. Use selective (those listed with a narrow range of activity) insecticides to preserve natural enemies.

A dermestid egg predator, Trogoderma sternale, is common in some areas of Southern California as is a small parasitic wasp, Telenomus californicus.

Use biological control and sprays of Bacillus thuringiensis on organically certified citrus.

Look for egg masses or larvae of western tussock moth in spring to determine moth numbers before damage occurs. If you find an average of one healthy egg mass per tree, economic loss may occur. Apply an insecticide after 90% of the eggs have hatched. If you monitor larvae, about 100 larvae an hour of search warrants an insecticide application.