Source: Cheryl Moorehead, Bugwood.org
It is rarely a pest in commercial pear orchards but may appear as sprays for other insects are reduced.
Adults are small (1/5 inch), black sawflies with transparent wings. Larvae are shiny black and sluglike with seven pairs of prolegs in addition to three pairs of true legs, and reach 1/3 inch long at maturity.
Pupae overwinter in the soil. Adults emerge in the spring and begin oviposition by inserting eggs into small slits in the leaf, laying two to five eggs per leaf. Females produce eggs without mating.
Larval feeding results in skeletonization of the upper leaf surface, leaving only leaf veins uneaten. Mature larvae drop to the ground and burrow into the soil about 4 inches to pupate. A second generation emerges midsummer and continues skeletonizing leaves. Second-generation damage is usually more severe, sometimes retarding tree growth the following year.
The extent of skeletonization should be observed weekly beginning in midsummer. No thresholds are available. Minor feeding is acceptable.