Yes. They can't fly if their body temperature falls below 10C (50F). And since their only method of warming themselves up is muscular activity, going out in the cold night air is literally suicidal! At 7C they become completely immobile.
My beekeeping books tell me that bees are "poikilothermic", which I repeat simply because it's such a wonderful word.
ETA: I don't have any info on bumbles, but you do see them in colder conditions, so maybe their minimum flying temperature is a degree or so colder.