There are four species of Megarhyssa in North America. One of them, nortoni, parasitizes siricids that feed in conifers. The other three are all parasitoids of Tremex columba, which feeds in hardwoods. From this image, I cannot tell whether or not the area along the basal vein is infuscated or clear, so all that can be said is that this is either macrurus or greenei. Perhaps the videos would contain a better view of the forewing.