No, this larva does not go with the beetle. I tried to rear this larva and a handfull of others I found in lupine stems. It's my first year ever trying to rear anything, and I wasn't expecting to need to do any such thing. Mother nature always has something up her sleeve for me. anyhow, the only one that even lived to the pupal stage was the Languria. Part of the problem may have been that the lupine stems dried up with time, and although I could replace them, I could not provide living stems, as these are deep rooted rare perennials. Any suggestions for next year's adventures appreciated...

I meant that I'm guessing the larva belongs to the same species, not that it was the same individual.

Unfortunately I have no experience with rearing stem-boring larvae, so I don't have much advice to offer, but I'm sure you're right that drying of the stem would be part of the problem. Although some stem-borers may be able to migrate from one stem to another, many (most, to my knowledge) complete their life cycle in a single stem, and wouldn't know how to enter a new one (although you might be able to trick them into doing so in some cases). Since you're getting a sense of the phenology of these insects, the obvious thing to try would be waiting longer before collecting the stems.

I just finished cropping 50 images of this individual trying to get a good leg shot! This is as good as it gets. The three pairs of prolegs are very visible, but I don't see much after that.

Yes, this was June 14, and the pupa we collected was Aug 28. Most of the other stems were empty on Aug 28 (2 were occupied, one with a pupa that was destroyed when the stem was opened, the one that was photographed and submitted to bugguide, 11 more had frass but were empty, 5 had intact pith). So next year I shall target some dates in late July and early August, perhaps I'll get more pupae and have more success that way.

Those six legs are the true legs, and I agree, there don't seem to be any prolegs (additional stubby leglike structures) beyond these--which supports my suspicion that this is a beetle larva. Thanks for digging through all those pics to find this one!