Insect identification > Homoptera > Aphids > Woolly apple aphids

Woolly apple aphids

The woolly apple aphid (Eriosoma lanigera Hausm.). - This European pest has been in the United States for many years and is widely distributed.

The adult is a small insect more or less completely covered by white, cottony or woolly threads of wax which practically conceal the louse beneath. Recent studies have shown that, in most cases at least, the winter is spent in the egg stage in crevices in the bark of the elm. The eggs hatch in spring and the young aphids pass to the buds and attack the leaves when these develop, causing them to become deformed, curled and clustered together, forming "rosettes." Several generations participate in this work.

During the later spring months winged migrants are produced and these pass to the apple, hawthorn and a few other related trees, where they locate on the underside of the leaves and produce young which crawl to thin places, wounds or water shoots and there locate and reproduce during the summer and fall until cold weather comes on, when migrating forms are produced which return to the elm where the eggs are laid.

This life history is complicated by the fact that during the summer some of the aphids migrate from the branches of the apple tree to its roots and feed there, producing knots and swellings which interfere with the nutrition of the plant and, if sufficiently abundant, may cause its death. These aphids are believed to remain on the roots the year around, generation after generation, but with their ranks recruited from time to time by migrants from the aerial members. Some of the latter also are believed to remain on the apple all winter as hibernating nymphs.

The amount of injury which this insect does to the apple above ground is not very great, except perhaps on nursery trees. Woolly spots at scars and wounds on the branches, noticeable chiefly in the fall, are not abundant enough to affect the trees much, usually. The root form, however, is sometimes quite injurious, particularly south of the latitude of Washington, and young orchards may suffer severely.

It is evident that elms growing near apple trees directly favor the successful migration of this pest, and as far as possible, therefore, no elms should be allowed to grow near apple orchards.