At least four species of wax scales (Coccidae) occur in California. Irregular wax scale, Ceroplastes irregularis, and tortoise wax scale, C. cistudiformis, generally are not pests.
Barnacle scale, C. cirripediformis, is a pest primarily in southern California on gardenia. It also feeds on citrus and many other hosts.
Chinese wax scale, C. sinensis, along the South Coast and in the San Francisco Bay Area is sometimes a pest on Australian willow, Escallonia, and mayten. Occasionally it is abundant on other hosts, including California bay, coyote brush, holly, Mahonia, and pepper tree.
Identification
Wax scale females are hemispherical and covered with thick, oily wax. Their predominant color is pale gray. Mature females range in size from 1/12 to 1/3 inch long. Their bodies have waxy ridges and white or dark-colored indentations or speckles. Nymphs are reddish, but their body is partially to almost completely covered with conical, stellate (star-shaped), or rosette-shaped, wax plates.
Life cycle
Barnacle scale adults are present from late July through winter. Early instar nymphs usually occur on the upper side of leaves. Third instar nymphs move to twigs where they mature into females and lay eggs beneath their body.
Chinese wax scale adult females are present from May through September. Egg hatch is most abundant in autumn. Males occur but are rare.
Wax scales apparently have one generation per year. Crawlers are most abundant during fall but may be present anytime from summer through winter.
Damage
Wax scales are occasional pests of various ornamentals. These Ceroplastes spp. can create a gooey mess on many different hosts by excreting copious honeydew. These infestations rarely, if ever, threaten plant health.
Solutions
Female scales commonly are killed by parasites, as evidenced by the round emergence holes in their body. Control ants, which attack the natural enemies of scale insects. Conserving natural enemies and applying horticultural oil or certain other insecticides are primary tactics for managing scales. If applying oil, thoroughly spray infested plant parts when crawlers and early-instar nymphs are the predominant stages.
For additional information, consult the Pest Notes: Scales and The Scale Insects of California Part 1: The Soft Scales.
