Pear Sawfly (Pear slug)

Distribution

Canada

Canada and United States

Micro-habitat(s)

Leaf, Soil

Damage, symptoms and biology

The first indications of the presence of the pear sawfly are the yellow spots on host foliage that are caused by the conspicuous, shiny black, sluglike larvae feeding on upper leaf surfaces. As feeding progresses, the affected areas on individual leaves enlarge and merge, until the leaves look bleached. Trees and shrubs appear scorched when their damaged leaves then turn reddish brown. The trees look unsightly due to the affected foliage, which may drop prematurely. Healthy trees can withstand several years of moderate attack because damage occurs in late summer, near the end of the growing season. The mucous-coated larvae may be a nuisance during years of high pear sawfly populations.

The pear sawfly, commonly called pear slug, is of European origin. Adult pear sawflies are small, black wasp-like insects, about 5 mm long, which emerge from mid-June until mid-July. Their eggs are deposited on the lower surfaces of the leaves. Larvae hatch in 9-15 days and migrate to upper leaf surfaces to feed, with each larva damaging several leaves before its development has been completed. When fully grown, larvae are about 11 mm long and have changed from black to a translucent yellowish green. Before the last molt, the front of the body becomes enlarged, concealing the head, and tapering toward the anal end. The larva secretes a slimy substance, which covers the body and gives it an olive-green colour resembling a slug. They then drop to the ground, where they overwinter in tiny, fragile cocoons spun just below the soil surface. Pupation usually occurs in the spring. There is usually only one generation per year, but in suitable weather a smaller second generation may complete development before winter arrives.

Main host(s)

American mountain-ash, cherries / plums, common pear, hawthorns, plum, quince, serviceberries