On Pinus palustris.
These European pine sawflies ate the innermost needles of all my mugo pines.
Could not positively identify the host plant because it was completely defoliated, but it was in a floodplain next to a blackwater creek. It definitely was not buttonbush. My best guess would be one of the Ericaceae...maybe Vaccinium (e.g. sparkleberry) 🤷