I believe the left two are larvae, and the right one is a puparium.

The tubercles on the putative larvae (with the two small, brown, disk-like (or hemispheric?) knobs at top) correspond to the (two fused) posterior spiracles...as does, I think, the small cylindrical looking protuberance at the "tail" of the putative puparium. I recently learned (from Microdon investigator Menno Reemer) that puparia typically develop a pair of well-separated anterior horns (=the anterior spiracles) about two days after pupation. I don't see such horns on the dark immature at right. Perhaps it's less than two days past pupation...or the horns are simply too small to be visible in the photo.

But I'm no expert, just an enthusiast who's been searching for literature and images on the web, and seeking out & receiving advice from the extended BugGuide community...trying to better understand Microdon!

Glad you posted this...definitely an intriguing addition to the Guide, vis-a-vis illustrating comparative differences in larvae vs. puparium and anterior vs. posterior (assuming my designations above are correct). I think many BugGuide Microdon posters and readers (including me!) have previously been uncertain about these simple questions.

A (speculative!) guess is that this may be (near to) species M. cothurnatus, per my comment here.

Was the species of Camponotus determined? It would be intriguing if the individual Microdon species were host-specific.