Damage, symptoms and biologyThe oystershell scale occurs generally throughout Canada and the United States. It attacks many species of shade trees including apple, white ash, white elm, basswood, and red maple. Of the shrubs, lilac is perhaps most frequently infested. Its infestations are common in ornamental plantings where trees are subject to various stresses. The insect sucks the sap from the branches and trunks of trees. This feeding retards growth, causes the bark to dry out and crack, and often results in the death of twigs and branches. In severe infestations, the bark may be completely covered with these scales and some trees may be killed.
The mature scales are brownish grey, usually curved, and resemble miniature oyster shells. The scales of both sexes are similar in colour and shape but the female scale, about 3 mm long, is considerably larger than the male. The elliptical, nearly white eggs overwinter in groups of 50 to 60 under the female scale. They hatch, about mid-June, into small white nymphs that crawl about for a few hours, then settle down to feed. They molt twice before becoming mature, and secrete a waxy material that becomes the protective scale. The females remain stationary for life and deposit eggs in early September. The males are winged. There is one generation each year.
Canadian Forest Service Publications
Diet and feeding behaviour
: Feeds on plant sap.
- Free: Moves about freely to feed.
Information on host(s)
It attacks many species of shade trees including apple, white ash, white elm, basswood, and red maple
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