What are your temps now?

The adults don't live for a very long time, at least relative to the amount of time spent in the larval stage of development. I don't think being overturned on their backs is an artifact of husbandry issues so much; I would think its more likely an accidental consequence of being crowded during breeding or something that cause them to flip over. Perhaps they cannot right themselves very easily... I never paid too much attention to the behavior of mine; they always seemed to just swarm together into giant, breeding masses and I left them be.