The Sawfly here described is a common pest on the leaves of various speices of Populus in Montana, and a Bulletin dealing with its life-histroy and economic significance is about to be published from the Montana Experiment Station. We give here an outline of its life-history, followed by descriptions of the two sexes.

The adults appear on the foliage in May and continue there for about eight weeks. The female deposits her eggs singly on the very young, tender leaves, and at the same time stings, them in such a way as to cause the edge to fold under on the lower surface.