In Western Montana, they'll fly at lower temperatures to take cleansing flights, if there's a sufficiently large cluster for warmth and/or the hives are wrapped in something like black tar paper.
For foraging, they'll fly down to about 43o F. I've not seen actual foraging at lower temperatures, but I'm basing this on the temperatures when we see our conditioned bees start to fly more than a few feet from the hive..I'd be interested in any verified reports of bees foraging at temperatures lower than 43.
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