I believe that you have to monitor the varroa mite infestation in your hives. Many hives do not even make it to winter because of viruses transmitted by the varroa mite. If they make it to winter, they may not make it through winter. This year (2017), bees coming through winter in okay shape saw a really rapid ramp up of the varroa infestation in the warm month we had before 10 days of freezing weather. Many of them didn’t survive the freezing weather.

So, please monitor your mites and treat if necessary.

This webpage from the Honey Bee Health Coalition is one of the best resources for understanding how to monitor for mites and includes information about the best options for treatment based on time of year or condition of the hive. There are great demonstration videos in addition to the pdf with an abundance of information.
http://honeybeehealthcoalition.org/varroa/

This is a not-so-great video I took in 2015 of state bee inspector, Don Hopkins demonstrating a sugar shake.

https://www.youtube.com/watch?v=enErclvPK58