Deformed Wing Virus
By no means is Deformed Wing Virus (DWV) the only thing that can kill a hive, but it certainly is more common that you think. Deformed wing virus comes from the Varroa Destructor and is one of the more obvious viruses to identify in a hive. Below are some symptoms of DWV:
The affected hive may have been one of your biggest in the fall.
When you opened the hive in the spring, it looks like your bees all left, not a lot of dead bees in the hive.
Bee poo left in the cells
Many bees stuck in cells, head first.
Little to no brood and what little brood is present has holes punctured in the cappings.
Some brood that never fully emerged scattered around the hive.
Remember, some of these symptoms can be associated with other issues as well. The more of these particular symptoms you have in the same hive, the more likely it was due to a large Varroa population.
To better combat Varroa issues, use a solid Integrated Pest Management system (IPM). Switch up the methods you use to control Varroa population and your success rate will be higher!