Cottony Cushion Scale

Common Name
Kingdom
Phylum
Class
Order
Family
Genus
Species
Cottony Cushion Scale
Animalia
Arthropoda
Hexapoda
Homoptera
Coccidae
Icerya
purchasi
scale
Natural History A small insect (4 mm) whose females are immobile on their host plant. Scale insects suck juices from the host plant, weakening it and also providing a disease vector. Females are covered with a wax secretion. Males have wings. Upon hatching the first instar, called a crawler, leap to the winds and are carried to other plants. Scale insects excrete a 'honeydew' which attracts ants and promotes the growth of sooty mold. The photo shows a vedalia beetle attacking a female scale insect (Photo: Max Badgley, Biological Photography, Sunnymead, CA).
Why this species? This insect was introduced from Australia to California in the last century and by 1888 was a serious pest on citrus trees. The nascent citrus industry was threatened with eradication. The head of the USDA, C.V. Riley, sent a person to Australia to look for some means to control the scale insect. He found the vedalia beetle (Coccinellidae:Rodolia cardinalis) and brought back 514 beetles. Within one year the progeny of those beetles had stopped the cottony cushion scale insect.

Seventy years later brought the widespread spraying of DDT. Soon the scale insects were DDT resistant and became a big problem because DDT still killed the vedalia beetles. Orchardist were paying $1 (in 1950's dollars) per vedalia beetle to get their biological control started again. Today, the vedalia beetle is susceptible to insect growth regulator sprays, while the scale insects are not. Orchardists are again seeking beetles to restore the biological control of scale insects.

The vining houseplant on the window sill has a scale insect on it. Look for the small white fluffs, those are the female insects!