Remarkably full hive after swarm

If there's a queen in the hive plus a queencell, there's a good chance that the older queen will leave (swarm) allowing her daughter to take over. Not good mentor advice to leave them like that.
Option if you suspect there's a roaming queen and are not sure, is to remove the queencell on it's frame to a nuc with sufficient bees to keep her warm and mate as an insurance policy .. or open all the queencells and leave them to it.

Was your old queen clipped?

jenkinsbrynmair said:

What gets me is that a lot of people on here use the word 'cast swarm' to describe a swarm of small size - that's nonsense. A cast swarm is one headed by a virgin queen and can be any size from massive to tiny. Just the same an 'large' swarm isn't neccessarily a 'prime' swarm.

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What is the success rate for a virgin queen starting a new colony?
Would the case be, new home, then out to be mated?

Cussword said:

What is the success rate for a virgin queen starting a new colony?

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Very good if there are drones and the weather is fair.
It's how all queens start out.

Sorry, I meant when she was in a cast. Does she have the same strong pheromones as a mated gueen.

The answer is the same.
If she gets mated successfully and she has enough bees to support brood rearing and the weather is good for forage then yes.
I collected a cast swarm in mid April last year (they swarmed in to one of my bait hives) and they built up so quickly they were making queen cells by mid June.
To answer your other question, newly emerged virgin queens are largely ignored by the other bees....there are exceptions....so their pheromone levels must be negligible.