is there any reason to continue rearing? I could put the cocoons in the yard and be done with the experiment.

A complete life cycle is always nice to have. I was getting jealous because you would beat me to it in nice warm CA. Mine are in no hurry to metamorphose as long as I keep them outdoors. Should I bring mine inside and speed up the process? : )
Also, I guess that you don't mind the devastation that they cause to your roses; plus the fact that they are an introduced pest which doesn't even belong here. From now on I plan to take measures in my garden now that I know who is making all those holes. No pesticides, though!

These two were so old when found--one molt away from pupating, if pupating rather than overwintering is what they're doing now--that they can't yield photos for a complete life cycle. It seems that the life of this species is pretty well known, anyway. So far, all I've added that's new is that a larva can spin an orange cocoon if it eats rust on rose leaves. That's hardly Columbus finding the New World. More like a sailor standing on an Italian beach in 1503 and reporting that he sees water.

How do you control them without pesticides? It's winter pruning time now. Roses here don't lose all their leaves in winter. I find tiny larvae of the same kind on the shoots I prune off. I don't know what to do except wait for jumping spiders to find them.