Drones are allways present.
IT is lack of mating weathers and temperatures what is needed in spring.
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B+ reported that the drones didn't have alot of semen for II.
You dont need mating weather for II.
My understanding is Drones like workers need good supplies of pollen for at least the first 8 days of life to 'mature properly'. I'm coming round to believe that a lack of pollen may be a 'silent' cause of colony demise, perhaps also affecting the potential fertility of drones? Pollen gets consumed rapidly during colony buildup & stores may only last a few days?