Wood-boring Beetle Parasitoids, Part 2

Last November I posted a picture of some wasp larvae a friend had found in the burrow of a wood-boring beetle larva while whittling by a campfire:

As I mentioned, I stuck them in the back of the fridge over the winter, along with the luna moth cocoon, walkingstick eggs, and so forth.  Some time in March I took them out, and they continued to wriggle slowly in place for several weeks.  When I checked on May 15, after not having a chance to look for about a week, there were several little adult wasps in the container.

Ross Hill on BugGuide.net tells me they are pteromalids.  Pteromalidae is apparently a hodgepodge of chalcidoid wasps that don’t fit into any other families, and it will probably be split into several families at some point.  I have also raised pteromalids from cynipid wasp galls, midge galls, and agromyzid fly leaf mines, as well as from pteromalid-induced galls on blueberry.  I occasionally find adults in the wild, like the one I showed visiting a bluet in my last post.  While I was photographing these wood-boring beetle parasitoids, some more continued to emerge from another hole in the piece of wood.

And, to round out the life cycle, here is one of the pupae, with the fully developed adult wasp plainly visible inside:

Every pupa I examined similarly had what appears to be the meconium (excrement deposited by the larva just before pupation) attached to the hind end by a string of some frizzy material.  Anyone who has an explanation for this, feel free to chime in.