Sawflies are part of the bee and wasp family of insects, and the only one that feeds on plant tissue. Normally, in both the juvenile and adult stages, sawflies consume all of the soft tissue in the leaf, leaving just the larger leaf veins. For deciduous trees, this places a significant stress on the tree. For conifers (evergreens), repeated defoliation by a sawfly can often cause the tree to die within a few years.
At first sign of the sawfly, spray the tree or plant with Borer-Miner Killer and repeat the spray every seven days until the infestation is controlled. When spraying is not possible, apply the Once-A-Year Insecticidal Drench w/Merit.