Pear Sawfly or Pearslug
The pear sawfly is a common pest in Iowa, attacking a wide variety of hosts. While it favors pear and cherry, it also attacks crabapple, apple, plum, hawthorn, cotoneaster, and mountain ash. The sawfly larvae damage these plants by feeding on the surface of the leaves, skeletonizing them, and leaving the network of veins.
The pear sawfly is one member of a group of insects sometimes called “slugs” because they superficially resemble true slugs. The bodies of these “slugs” are largest just behind the head and taper toward the tail end. The sawfly adult is a harmless wasp.
This insect overwinters in a cocoon 2 to 3 inches below the soil surface. The adults emerge from the ground in late spring (May and June). They resemble shiny, black flies, about 1/5 inch long, with darkened wings. Female sawflies insert eggs into the leaves of a host plant. After 1 to 2 weeks the eggs hatch, and young larvae begin to feed as a skeletonizer on the upper surface of the leaf.
Leaves fed upon by the larvae quickly turn brown, as only a thin layer of leaf tissue is left on the veins or skeleton of the leaf. Damaged leaves may curl or drop prematurely. Defoliation, which may range from spotty to complete, is not usually fatal to healthy, well-established trees, though they may be stressed or weakened.
Pear sawfly larvae are yellow but usually appear olive green or black because of a covering of secreted slime. The mature "slug" is about 1/4 to 3/8 inch long. Larvae feed on the leaves for about 4 weeks. When full grown they drop to the ground, burrow into the soil, pupate and emerge as adults that produce a second generation in late July or August.
Any management of pear sawflies must commence while the larvae are still small. Most often, damage is noticed when the sawflies are nearly full-grown or have finished their development and treatment is no longer warranted.
Pear sawfly larvae can be physically removed from infested trees if there are only a few on small trees. If handpicking is not practical, and heavy skeletonizing is apparent, chemical control may be necessary. Be sure both larvae and a serious damage potential are present before beginning a spray program. Sprays applied after larvae have left to enter the soil do no good.
Most garden or landscape insecticides can be used to control sawfly larvae when control is warranted. Be sure the specific host is listed on the insecticide label before you use the product. Do not apply insecticides that are toxic to pollinators on plants that are in bloom. Read and follow label directions.