Note clubbed antennae. Green with two white lateral stripes. Rounded head capsule directed downwards. Larvae feed on single needles, gregariously at first, later they feed individually. During epidemics they may consume the entire needle, both old and new.
Mature trees are more susceptible than younger, more vigourous trees.
The effects of larval feeding are seldom evident, except in 1961 it became necessary to spray 650 hectares of Douglas-fir on Vancouver Island.