Pear sawfly (cherryslug, pearslug)—Caliroa cerasi
Pear sawfly (Tenthredinidae) is a wasp (Hymenoptera) named for the females' jagged (sawtoothed), egg-laying organ. The larvae chew foliage of cherry, pear, and occasionally other Rosaceae.
Adult pear sawflies are about 1/5 inch long and glossy black overall with yellow. They have two pairs of wings with prominent veins and a broad waist, unlike the narrow constriction between the abdomen and thorax of most wasps.
Larvae are whitish to yellow with a yellowish-brown head when they are newly hatched, recently molted, or mature (prepupae). After molting as they begin to feed, larvae exude a gelatinous, olive-green coating that obscures the body surface and gives them the appearance of a slug (shell-less mollusk). Larvae grow to about 3/8 inch long. The thorax, three segments immediately behind the head, is wider than the rest of the body.
The California pear sawfly, Pristiphora abbreviata, also feeds on pear; its larvae are bright green and lack an olive-green coating. In addition to three pairs of true legs behind the head (obscured by the body coating), pear sawfly larvae have prolegs (fleshy stubs, or leglike appendages) on abdominal segments two to eight (seven pairs) and a clasperlike rear end. Most other caterpillarlike larvae that occur openly on foliage have five or fewer pairs of prolegs.
Pear sawflies overwinter as inactive, mature larvae (prepupae) in cells they form in topsoil. In early spring, they pupate and emerge as adults and mate. Females insert tiny eggs in the underside of host leaves. Larvae soon hatch and feed and develop through five, increasingly larger instars (growth stages). At maturity, they drop to the ground, move into topsoil, and form a pupation cell.
There generally are two generations per year in California. Larvae are most abundant in mid to late spring and mid to late summer. Feeding by the second-generation larvae during summer causes most of the foliage damage.
Larvae chew and skeletonize cherry and pear foliage and also feed on cotoneaster, hawthorn, mountain ash, plum, and quince. They feed on the upper side of leaves, chewing surface tissue except for the veins and causing brownish to gray patches in foliage.
Pear sawfly and its damage in California occur mostly in coastal and northern areas. Feeding by high numbers of larvae may reduce fruit size that season and result in fewer or smaller fruit or both the following season. Pear sawfly feeding does not seriously threaten the survival of otherwise-healthy plants.
Pear sawfly is often controlled by natural enemies. When limited in numbers, pick the pearslugs (cherryslugs) off by hand or dislodge them from foliage with a forceful stream of water.
Larvae are relatively easy to control if thoroughly sprayed with almost any insecticide, including horticultural or narrow-range oil, neem oil, insecticidal soap, and spinosad. Spinosad can adversely affect bees and certain natural enemies. Because it is toxic to bees for several hours after the spray has dried, do not apply spinosad to plants that are flowering.
Bacillus thuringiensis (Bt) does not control sawfly larvae because they are not caterpillars, which are the larvae of butterflies and moths (Lepidoptera).
Avoid applying broad-spectrum, persistent insecticides, such as carbamates (carbaryl, or Sevin), organophosphates (e.g., malathion), and pyrethroids (e.g., bifenthrin, cyfluthrin, fluvalinate, and permethrin); these are harmful to bees and natural enemies and some products move to contaminate surface water and adversely affect aquatic organisms.
See Pear Sawfly from Oregon State University for more information.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).