Because of the virtual disappearance of American elm trees, the woolly apple aphid most often lives on apple trees throughout the year. Each group of aphids, small or large, is considered a colony. Aphids are present more nearly year round on the roots than on the tops. The aerial forms are most commonly found on the twigs, water sprouts and callus tissue in wounds, cankers and scars. Wingless females in the aerial colonies may give birth to nymphs at any times in spring, summer or fall.
Newborn nymphs are very important in the spread of the woolly apple aphid.
They spread either through some mechanical agency or directly by crawling. Birds and insects can also transport aphids. Any unsettling conditions will produce crawlers, though they are generally more abundant in spring and fall. Crawlers cannot work into and through the soil. In orchards, the swaying of trees in the wind, and organic matter, clods, stones and other objects may provide pathways to the roots.