temps below 45 pretty much will kill them. Even if it doesn't they don't seem to morph into beetles, the pupa die. At least thats been my experience so far. I tried slowing a batch down in the fridge to stagger my bins more, and lost most of them when they went into pupas. I did pull them out about once a week, and feed them. They like being pretty warm. Some people even keep them in incubators.