Woolly apple aphid

Erisoma lanigerum

Hosts

Apple, Crabapple, Elm, Hawthorn, Mountain ash and Pear

Appearance and Life Cycle

Description of this image follows
Late spring colony in leaf curl.
Photo credit: Whitney Cranshaw, Colorado State University, Bugwood.org

Description of this image follows
Leaf curling injury on a hybrid elm.
Photo credit: Whitney Cranshaw, Colorado State University, Bugwood.org

The woolly apple aphid overwinters in the egg stage in elm bark crevices. In the early spring, a bluish-white, stem-mother (wingless female) emerges and feeds on the unfolding terminal buds and leaves. The mature stem-mother gives birth to numerous, wingless females which feed on the terminal leaves, causing the leaves to curl, forming rosettes. The second generation gives birth to a third generation of winged females. This generation migrates to their secondary hosts, apple and related trees, and produces generations four and five. Fourth and fifth generation aphids have yellowish to rusty-brown bodies, which are hidden with white, wool-like wax. They feed on twigs and roots forming large, warty galls, severely affecting tree growth. In September, a sixth generation of winged females migrates back to the elm trees and produces sexual males and females. The sexual forms are small, wingless and reddish-yellow to reddish-brown. After mating, females deposit a single, purplish, slightly flattened, oval-shaped egg in the bark crevice of an elm tree to complete the life cycle.

Damage

Woolly apple aphids cause damage by feeding on the sap of host trees. In the spring, the aphids feed on the terminal leaves of elm trees forming rosette-type deformations. The rosettes are unsightly, but no permanent damage occurs. In the fall, aphids feed on secondary hosts, forming galls which seriously affect tree growth. Damage makes the trees more susceptible to attack by other insects and diseases.

Control

Control can be achieved by pruning and destroying the aphid-filled rosettes in the spring. Diazinon or malathion can be applied just before bud break and again 10-14 days later.

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