This species is a minor pest of apple. The larvae feed gregariously, often coating the foodplant with masses of characteristic webbing. Heavy infestations may lead to considerable defoliation and significant fruit loss. Attacks occur most frequently on unsprayed trees, such as those in mature private gardens and old, neglected orchards. This and other closely related species (the latter associated with plants such as Crataegus monogyna, Euonymus europaeus, Primus avium,
P. padus, P. spinosa and Salix alba) are collectively known as 'small ermine moths'.
Moths are active in July and August. Eggs are laid on shoots and spurs in long, oval or elongate, raft-like batches of up to 80 or more and then coated with a protective secretion that hardens soon afterwards. The eggs hatch in the autumn. The larvae then congregate and overwinter between the remains of the egg raft and the underlying bark. In the early spring, the larvae invade the opening buds; later, they mine gregariously within the expanded leaves to form large blotches. Second-instar larvae vacate the mines to feed externally in communal webs, attacking both leaves and blossom trusses. Infested shoots and branches may become coated in webbing. The larvae are fully fed in June. They then pupate in white, opaque cocoons spun in groups within the web. Adults appear about 2 weeks later.
Adult 18-22 mm wingspan; forewings white with a characteristic pattern of small white spots; hindwings grey (Fig. 275). Egg flat, dark purplish-grey and laid in a large batch. Larva up to 20 mm long; body dirty yellowish-grey; head, pinacula and dorsal plates black (Fig. 276). Young larva mainly yellowish-white; head andprothoracicplate brown. Pupa 10 mm long; mainly yellow but head, thorax, wing cases and tip of abdomen darker; penultimate segment with a distinct ventral hump; cremaster with six long filaments.
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