Common Name: Euonymus scale
Scientific Name: Unaspis euonymii Comstock
Description: Full-grown male scale insects are elongate, 1/32-inch long and mostly white, with ridges along the tops of their bodies. Adult males emerge from these scales as tiny two-winged insects. Female scale insects are larger, almost 1/16-inch long, brown and shaped like an oyster shell.
Life Cycle: Life cycle is intermediate. Winged adult males emerge and seek female scale insects and mate. Before dying, females produce a cluster of eggs underneath the scale shell. Six-legged, mobile yellow nymphal forms called “crawlers” hatch from the eggs and crawl to newly-formed foliage. Nymphs develop through several stages (instars) before reaching maturity. There are two or three generations per year, with eggs of the first generation hatching from April to June. However, all stages of development can be found during most of the year.
Habitat, Food Source(s), Damage: Primarily found on evergreen euonymous (Euonymous japonica and E. kiautschovica), this species also infests celastrus, camellia, eugenia, hollies, pachysandra and twinberry. Scale insects on leaves are predominantly the white males, occurring mainly on the underside of the leaf until they become numerous. Their feeding activity extracts juices from leaves and results in yellow spotting visible on the upper leaf surface. Yellow discoloration progresses until the leaf dies and drops from the plant. Brown female scale insects are more commonly found on the twigs and stems. Whole branches or entire plants can die of heavy infestations.
Pest Status: Infests certain varieties of euonymous, causing leaf drop, plant stress and occasionally death of heavily infested plants; medically harmless.
Literature: Carter et al. 1980; Whitcomb 1983.