Wikipedia
Diprionidae
The Diprionidae are a small family of conifer-feeding sawflies (thus the common name conifer sawflies, though other Symphyta feed on conifers) restricted to the Northern Hemisphere, with some 90 species in 11 genera worldwide. Larvae are often gregarious, and sometimes there can be major outbreaks, thus these wasps can be major forest pests at times.
The family is distinctive in having antennae with about 20 flagellomeres, and serrate or pectinate.