Scutellum with black anterior margin unlike typical simillima, along with darkened proboscis, darkened hind legs.... but also lacks yellow spot on transverse suture of scutum of typical tenthredinoides..... either way, this is a melanistic unusual form. Scutellum closer to tenthredinoides than simillima, while scutum seems closer to simillima than tenthredinoides... however, given this is melanistic it seems possible that the transvere suture spot would be indistinct. I would still lean tenthredinoides, perhaps this is best left at genus?

Based on Webb 1984 and iNaturalist maps, tenthredinoides seems to occur farther north than simillima, which is a strictly midwestern species not entering into the northeast beyond western NY. So I think this should be placed in tenthredinoides.

yes, you got some good points there, especially with the distribution... difficult case

Palpi look yellow, although proboscis partly black...? so not aterrima? Rather a tenthridinoides?

Thanks Martin for this id..

Thanks Norm..