What to feed adult banded tussock moth?

I tried to keep my overwintering cocoons by the window but I supoose it was still a bit too warm for them so one emerged early. It's far too cold outside to release. Not many people end up raising these guys and especially don't keep them as adults but I am in a weird position. It has a mouth and definitely can feed and drink. I've offered water an juice as a go-to but from what I've read they like to eat "the liquids of decaying plants that are rich in alkaloid compounds." Any suggestions?

For context: I ended up raising these guys from eggs because a moth laid her eggs in my room before dying. I hoped they would emerge in spring but this one had other ideas.