Forest Pests: Insects, Diseases & Other Damage Agents

Oystershell scale insects feed on many species of deciduous trees by sucking sap from the twigs. Damage is usually light, but some species, particularly ash, can die if infestations persists. Dead and dying branches and abnormally small or discolored leaves are the first indications of this scale. Close examination of the twigs reveals a flattened, elongated, brownish bump that looks like a minature oystershell. These females scales are about 1/8 inch long. Males, which have two wings, antennae, and eyes, but no mouth, are rare.

The female lays eggs under her shell in late autumn, where they remain until they hatch in late May. The crawlers move around until they locate a suitable feeding site, then insert their mouthparts and begin to feed. Oystershell scale spreads during the crawler stage when wind, birds, large insect, and other moving objects transport the young scales. As the insect grows, the shell covering increases in proportion so that the body is always protected. The female loses her legs and eyes after molting from the crawler stage, and she becomes no more than a lump with a mouth. Most of her body is filled with 20 to 100 eggs which she lays in late autumn. She dies a short time later. There is one generation per year in the North.

Life Cycle ; the "armor" may be lifted to expose a tiny legless adult female or batch of eggs Photo by E. Bradford Walker, Vermont Department of Forests, Parks and Recreation

Infestation; infestations are usually confined to small portions of trees Photo by E. Bradford Walker, Vermont Department of Forests, Parks and Recreation

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