Moved from ID Request. What you now have is the prepupal stage--it won't feed anymore, and it will seek some wood to bore into to pupate and overwinter. I tried to rear some Macremphytus last year and they chewed their way out of the plastic bags I was keeping them in and then I recovered one that was trying to bore into my window sill, and another that was caught in a spider web... there was some sawdust under a chair, and I never did track down the one that caused that. I gave them some punky wood in a jar, and they bored into it and overwintered there; still haven't emerged. Sawflies can take more than a year to emerge (or mine might be dead; hard to say). Apparently giving them corks to bore into will work too.