right now I have the opposite problem! (They grow faster in the warm months.) Too many are pupating before I get to harvest them. So I'm putting some in the fridge to hold them back; it slows down their metabolism.How do you guys decide how many to harvest? I'm still a few months from that point, but I would hate to harvest too many and have to essentially start over.
To answer your question, each female beetle should lay about 200 eggs, so you should be able to harvest at least 3/4 of any batch and still expect to reproduce as many or more than you started with.