Your climate seems similar to mine, at least in winter lows. A colony of BSF will endure cool weather for quite a long time, provided they are well fed and given some insulation. The grubs will ball up together and generate their own heat. But they will not grow as fast and fewer will "crawl off" as mature prepupae for
feed. The other problem is that adults will not hatch out and mate and lay eggs for a new generation until it is proper summer. So you might get some good grub yields in the fall as the weather is cooling, and another in the spring from the overwintered colony, but they will overwinter just maintaining. You would need a warm
greenhouse with the bin in there, and let some grubs hatch out and fly around and mate and lay eggs back in the bin for reliable winter production. The other possibility is to breed up extra large colonies during the warm weather and store the excess grubs.....perhaps in cool storage, or perhaps dead and dried? for winter feed. Or switch to red
compost worms in the winter.....these don't mind cooler temps.....