On average, 20% of unmanaged bee colonies may die during winter.
In managed hives this figure can vary from around 5% to 100%, depending on the measures taken in autumn to prepare for winter.
The prime consideration for over-wintering bees is to keep them alive and in reasonable condition to come into the spring.
If they survive into spring, their numerical strength and disease status will largely depend on what management practices were adopted in autumn, not what is done in winter.
Points to be considered are: