Life history and habits

Pear sawfly adults emerge from cocoons in late spring or early summer. They are slightly larger than a common house fly and are yellow and black in color. The adult wasps begin laying eggs in the upper portion of leaves on preferred host plants. The larvae hatch one to two weeks later and begin feeding on leaf tissue for about four weeks. Pear sawfly larvae consume the tissue between leaf veins, a feeding behavior that results in skeletonization of the leaf. After feeding for about four weeks, larvae pupate in the soil. 

A second generation of pear sawfly adults emerge later in the summer and is usually the leading cause of high population densities and greater potential for crop injury later in the growing season. When populations become large enough, every leaf on the tree can be visibly injured, though this is not usually fatal. Larvae from this second generation will overwinter in the soil as pupae, giving rise to first generation adults the following year. 

Cultural control

Larvae can be physically plucked from leaves and placed in a bucket with soapy water, or they can be flushed off the plant with a strong stream of water. 

Chemical control

Bacillus thuringiensis (Bt) applications and soil drenches are not effective management options for this pest. 

Insecticides (see resources below for details) should only be used when larvae from either generation are present; insecticidal sprays will not affect larvae after they enter the soil to pupate. Avoid applying insecticides during bloom periods when pollinators are active. It is always recommended that you rotate insecticides that are applied each year in order to prevent insecticidal resistance from developing over time.