The woolly aphid, Eriosoma lanigerum, is a serious worldwide apple pest. It is probably of North American origin and has been distributed to other parts of the world mainly via infested apple rootstocks. It can occasionally also be found in pear, quince and a few other woody Rosaceae.
Life cycle and appearance of Woolly apple aphid
In contrast to other aphids, the life cycle and survival from year to year of the woolly aphid depends entirely on wingless, parthenogenetic and viviparous forms. Sometimes a few wingless egg-laying females are produced in autumn but their eggs do not develop further.
Adult viviparous (wingless) females of the woolly aphid are 1.2-2.6 mm long, purplish brown and covered by masses of white, mealy wax. The siphunculi are pore-like and the cauda is small.
Eriosoma lanigerum overwinters as “naked” nymphs (without wax covering) on apple trees sheltering in cracks and under loose bark. The nymphs become active in late March or April (in the northern hemisphere) and around the end of May, large colonies covered by conspicuous white, sticky “wool” can be seen, mainly on spurs and branches.
Many generations occur during the summer months, also on new growth. Water shoots arising from the trunk or main branches, are very frequently attacked. The aphids mainly spread through young, wingless
nymphs which crawl or are blown by the wind from tree to tree. Sometimes a few winged aphids are produced in summer.
Winged egg-laying females are produced in early autumn but their eggs do not develop.
Contrary to the situation in America, South Africa, and Australia, woolly aphid does not infest roots in Europe (except rarely if they occur above the ground) or the subterranean basal part of trunks.
Galls are often produced on infested wood. These galls may seriously disfigure young trees and nursery stock. If the galls split they may allow entry of pathogenic fungi such as Gloeosporium rots or apple canker. Woolly aphid does little direct harm to mature trees but the sticky masses of “wool” may contaminate leaves and fruits and can be a nuisance at harvest time.