How to Manage Pests
UC Pest Management Guidelines
DESCRIPTION OF THE PEST
The pear sawfly, commonly known as pearslug, is not a true slug but resembles one because it exudes a slimy olive green coating over its slug-shaped body; it is actually the larvae of a sawfly. Pearslugs overwinter as pupae. Adult sawflies emerge in spring and are small (about 0.2 inch or 5 mm), shiny black, wasplike, flying insects. Female sawflies lay eggs in the upper surface of leaves, preferring the leaves in the upper portion of the canopy.
Newly hatched larvae are white with a yellowish brown head, turning completely yellow when mature. Soon after they start feeding, however, they cover their bodies with the slimy coating that makes them appear almost black. When mature, the larvae are about 0.5 inch long; the anterior end of the body is wider than the rest of the body. They drop to the soil to pupate. There are two generations a year, with the second generation generally being larger in number than the first and quicker to develop from egg to pupa.
Pearslugs skeletonize foliage by removing all leaf tissue except the fine network of veins. Damage from both generations can reduce fruit size at maturity. If the second generation causes extensive defoliation of trees, bloom may be reduced the following spring.
Pearslug is often under effective biological control, but in recent years it has become an increasing problem in mating-disruption orchards where broad-spectrum cover sprays are no longer used but populations of natural enemies may not have adequately reestablished.
In backyard trees or organically managed orchards, if a potentially damaging population develops, washing the tree with water from a garden or sprayer hose will dislodge them without disrupting parasites and predators.
Organically Acceptable Methods
Biological control and spray.
Monitoring and Treatment Decisions
In orchards with a history of pear sawfly, start looking for eggs in top shoot samples in April. Continue monitoring top shoots from 20 trees per orchard for larvae throughout the growing season and after harvest. Spot-treat localized infestations in these orchards to prevent them from spreading. For more information regarding sampling for additional pests during the growing season, see SAMPLING DURING FRUIT DEVELOPMENT and POSTHARVEST SURVEY.
UC IPM Pest Management Guidelines:
Insects and Mites
L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County