The books / Queen Rearing / chapter 3 of 5
Mating flights
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A virgin queen leaves the hive on a warm afternoon, flies to a drone congregation area and mates with ten to twenty drones. She never mates again. About 70 to 90 percent come back mated; the rest are taken by birds, lost, or return to a hive that isn't theirs. She starts to lay three to five weeks after the graft.
Try this in the game: Only graft between mid-April and August: before and after, there are no drones to mate with.