How to Manage Pests

Pests in Gardens and Landscapes

Seasonal development and life cycle—Gall wasps

Adult female gall wasps or midges deposit eggs in or on plant tissue. Gall development is poorly understood, but galls generally form several weeks or months after eggs hatch. Larvae feed under the plant tissue; their secretions apparently induce abnormal growth of cells in the plant. Many galls harbor a single, legless larva. Other galls may harbor several larvae, some of which may be different species that are predators or parasites of the gall maker. Among these unusual species is the jumping oak gall wasp, Neuropterus saltatorius, which causes discolored spots on the upperside, and seedlike deformations on the underside, of valley oak leaves. Galls drop in summer from the leaves. Huge numbers may be seen hopping an inch or more above the ground because of the movements of a tiny wasp larva inside each gall.

Galls caused by the jumping oak gall wasp
Galls caused by the jumping oak gall wasp; wasp larva inside each gall

Young green oak apple galls
Young green oak apple galls; darkolder galls


Statewide IPM Program, Agriculture and Natural Resources, University of California
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