Females insert their eggs in young willow leaves and inject a fluid that causes the formation of reddish, berrylike galls. These insects apparently do not harm the plant, but heavily-infested plants can be aesthetically unattractive. The insects responsible for these galls are not often seen. Management of Sawflies. Healthy trees and shrubs tolerate moderate defoliation without significant loss in growth, flowering, or fruit yield.
Natural enemies help to eliminate many of our sawfly larvae.
Oak gall wasps. Hundreds of different types of gall wasps occur in the U.S., and are especially abundant and varied on oak. Eggs are deposited in plant tissue and a gall begins to form several weeks or months after the white larva has hatched and begun to feed. Species identification is more easily based on the gall than on a description of the insect. These insects do not greatly harm the trees, although it can be unattractive.