Macremphytus tarsatus or M. varianus
Pest description and damage Dogwood sawfly is a recent introduction to the Pacific Northwest. The species is presumed to be M. tarsatus but has not been verified by experts as adults have been difficult to find/rear. They have only been found feeding on red osier dogwood, Cornus stolonifera. Eggs are small bumps under the epidermis of leaves. Newly hatched larvae are yellow-green. The next instar is covered with a white waxy material which is shed with the final molt; third instars are yellowish-green with rows of bold square dark spots along the body. Entire large red osier dogwoods have been defoliated by summer's end. Larvae cause further damage when they burrow into wood-including nearby siding on buildings-to pupate.
Biology and life history Eggs hatch from the underside of the leaf and small larvae cluster together to begin feeding in July. Larger instars begin to defoliate trees in late summer, often in late August. Larvae pupate in rotting wood, house siding or soil in fall and emerge in late spring to lay eggs.
Pest monitoring Newly hatched larvae congregate in clusters in leaves at the tops of trees. From below, the clusters of larvae are visible as sunlight penetrates the thin leaves, revealing dark clumps.
Prune out infested branch tips at the tops of trees when larvae are first noticed.
It is likely that native predators and parasitoids will find this food source but no records have been noted.
See "Sawfly" in:
For more information
Johnson, W.T. and H.H Lyon. (1991). Insects That Feed on Trees and Shrubs. 2nd ed., Cornell University Press.
Rosetta, R. 2008. Dogwood sawfly (http://oregonstate.edu/dept/nurspest/dogwood_sawfly.htm)