California pear sawfly—Pristiphora abbreviata
Sawflies (Tenthredinidae) are wasps (Hymenoptera) named for the females' jagged (sawtoothed), egg-laying organ. The California pear sawfly is an occasional pest of pears.
Adults are stout wasps about 1/4 inch long with two pairs of wings with distinct veins. They have a black body with yellow on the legs and prothorax, the area immediately behind the head. Adults have a broad waist, unlike most wasps that have a narrow constriction between the abdomen and thorax.
Larvae of California pear sawfly are bright green and up to 1/2 inch long. The head is light brown with a small, black, eye spot on each side. In addition to three pairs of true legs behind the head, the larvae have pairs of prolegs (fleshy stubs, or leglike appendages) on abdominal segments two to seven (six pairs) and a clasperlike rear end. Most other caterpillarlike larvae that occur openly on foliage have five or fewer pairs of prolegs.
The green body of California pear sawfly can be hard to spot on leaves, especially because larvae commonly feed with their body aligned along the inside edge of holes they are chewing. When California pear sawfly feeds along leaf margins, the damage can resemble the half-moon-shaped cuts of leafcutting bees, which are beneficial pollinators.
Note that the pear sawfly (cherryslug, or pearslug) is a different, more-damaging species. Unlike California pear sawfly, larvae of the pear sawfly excrete an olive-green coating that gives the appearance of a slug (shell-less mollusk).
Sawflies develop through four life stages: egg, larva, pupa, and adult. The California pear sawfly overwinters as a mature, inactive larva (prepupa) in a silk cocoon in litter on the ground and in topsoil. Pupation and adult emergence occur in early spring.
After mating, females insert tiny, translucent to white eggs singly into leaf tissue, commonly in the margins of leaves in the lower part of the tree. Most eggs hatch by petal fall and the larvae immediately begin feeding as they develop through several increasingly larger instars (immature stages). Larvae mature about May, then drop to the ground to overwinter. There is one generation per year.
Larvae of California pear sawfly and their feeding damage occur only during spring. The larvae chew circular holes in leaves. When larvae are abundant, entire leaves can be consumed except for the midrib. Otherwise-healthy trees can tolerate a significant amount of leaf chewing without threatening tree health.
Birds, predatory wasps, and other natural enemies feed on this sporadic pest. Natural enemies sometimes cause a dramatic decline in the abundance of sawfly larvae over a relatively short period of time.
California pear sawfly is not commonly abundant in California and the larvae do not feed on fruit. Generally no control is recommended. For more damaging species, see Pear Sawfly (Cherryslug, Pearslug) and Sawflies.
Adapted from Pests of Landscape Trees and Shrubs: An Integrated Pest Management Guide, University of California Statewide Integrated Pest Management Program (UC IPM).