Adult -The apple aphid varies in size from 1.8 to 2.6 mm and in color from yellow to light green or dark green. The head, tips of the antennae, legs, and cornicles are dark. The stem mother is somewhat darker than other forms and is sometimes covered with a waxy bloom. The male is elongate, and the female is round. This aphid may be wingless or winged, or possess small wing remnants. Wings, if present, are transparent with brown veins and a smoky stigma.
Egg -The egg is oval, flattened on the side next to the bark. It is 0.6 mm long and 0.3 mm wide. Initially yellow (rarely green), the egg turns black.
Nymph -The first instar is dark green with dusky appendages. The nymph's color lightens as the nymph matures.
Host Plants -Crabapple, hawthorn, mountain ash, and pyracantha are hosts for the apple aphid. The ornamental plants attacked by this insect are secondary hosts.
Damage -As they feed, apple aphids cause the foliage of terminal growth to curl. They also excrete honeydew (a nuisance) in which sooty molds sometimes grow. Heavily infested plants are often sticky with honeydew, dark with sooty molds, and disfigured by distorted new growth and cast aphid skins.
Life History -Overwintering as eggs on suckers and the terminals of trees, the aphids hatch in early spring and appear on the buds as the first leaves are unfolding. Throughout most of the year only females, which give birth to live young, are produced. The females that hatch from the overwintering eggs are called stem mothers. More than half of the offspring of the stem mothers are winged, and the first major dispersal occurs. This migration takes place in late May or early June. Winged individuals are produced throughout much of the summer but are most numerous in early summer.
Each female produces about 50 nymphs in a period of about 30 days. Stem mothers produce more offspring than succeeding generations. A female produces young aphids about 1 day after its final molt. The four nymphal instars develop within 2 weeks. As many as 16 generations can be produced in 1 year.
The apple aphid is most abundant from mid-June to the beginning of August. In early September, male and female aphids appear and mate. Mated females deposit one to six eggs, which develop partially before the first frost.
Populations of the apple aphid undergo fairly regular fluctuations in density throughout the summer. Because the aphid feeds only on new growth, the density of the populations is regulated somewhat by the growth of new shoots.
For specific chemical controls, see the current state extension service recommendations.
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