Weak and queenless colony management
At the beginning of Spring, weak colonies can be lifted to the top of a strong colony to get some extra heat. The upper colony should be separated with a queen excluder and a newspaper sheet from the underlying colony. Alternatively, you can give the weak colony one or two sealed brood combs with young bees from an excessively strong colony later in spring. Queenless colonies can be united with a queenright colony with newspaper.