What about something internal to the bees as a signal for late winter brood
rearing to start? At some point, if the queen does not start laying the
colony will be lost from the winter bees dying off.

Fat body depletion causing a pheromone to be released that stimulates the
queen to lay? Or a pheromone that changes with the age of the bee?

David Baker
To Bee or Not To Bee

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