How to Manage Pests

Pests in Gardens and Landscapes

Willow gall sawflies—Euura and Pontania spp.

Various sawflies (Tenthredinidae) induce distorted swellings, or galls, on the foli­age, terminals, or twigs of willows, Salix spp.

Identification

Willow galls are caused by several species of sawflies and other pests. Willow beaked-gall midge, Mayetiola rigidae, causes infested shoot tips to swell and the nearby leaves to drop, leaving a twig gall that may have a point, resembling a beak. An eriophyid mite, Vasates laevigatae, causes numerous tiny, green swellings in leaves, resembling beads.

The willow leaf gall sawfly, Pontania pacifica, commonly causes green to reddish berry­like galls on Salix lasiolepis foliage. Each gall may be globular or elongate and up to 1/3 inch long. The galls are quite variable in size, shape, color, and number per leaf.

Willow leaf gall sawfly adults are stout, broad-waisted wasps. The males are shiny black, and females are dull reddish. Larvae are legless and light green, yellow, or whitish with a light brown head. The last instar larva is approximately 2/5 inch long. The cocoon is oblong, 1/4 inch long, and reddish brown to creamy white. Externally the cocoon is covered with pieces of plant debris and soil particles.

Life cycle

Willow leaf gall sawfly females insert eggs in young willow leaves. The leaf forms a gall at each location where an egg is laid. The maggotlike larvae feed inside the leaf galls and develop through five instars (males) or six instars (females).

The last-instar larva molts into a prepupa, which emerges from the gall and drops to the ground. The prepupa spins a silken cocoon in which it pupates into an adult. This insect apparently has several genera­tions per year.

Solutions

Willow gall sawflies do not harm plants. No controls are recommended or known.

The larvae of several wasps, and at least one weevil and moth, feed on the sawfly larvae or on the gall tissue, causing the sawflies to die. A Eurytoma sp. wasp appears especially important in reducing galling by P. pacifica.

Willow leaf gall sawfly galls
Willow leaf gall sawfly galls


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