Queenlessness is probably the main cause of hive death during the beekeeping season – but it doesn’t have to be. A hive can lose its queen for several reasons – swarming, supersedure, beekeeper error, etc. Any time a new queen flies out to mate there is a significant chance that she won’t make it back.
When a strong hive becomes queenless for any reason you have about 4-5 weeks to take action to save the hive, but the sooner you do something the better it will be. This is one reason that we do inspections.