Helped with a great class given by the MVBA for intermediate beekeepers last weekend, where they talked about how to manage overwintered hives.
In my opinion, one of the most important beekeeping topics is controlling varroa mites to keep hives strong and healthy. Beekeepers who do not monitor and appropriately treat their hives for varroa mites are spreading diseases within their own hives, other colonies, and native bees. I recently read a great article by Meghan Milbrath at Michigan State University Extension that I think everyone should read! It's titled Keeping Honey Bee Colonies Safe from the Varroa Mite.
The guidelines for acceptable counts of varroa mites have decreased yet again this year to 1-2 mites/100 bees. Everyone should be familiar with performing mite counts using either a powdered sugar shake or an alcohol wash of 1/2 cup of bees (approx. 300 bees). Just google how perform these sampling methods if you are unsure.
As mentioned in class, there are three types of methods to control the varroa mites:
Physical measures: examples include using screened bottom boards with mite sheets, drone frames, sugar dusting, and requeening with more resistant stock
Soft treatments: using naturally occurring pesticides like formic acid or thymol based treatments like Mite-Away or Apiguard.
Hard treatments: using synthetic pesticides like Apivar and Apistan.
I recommend that a beekeeper use a combination of physical measures and soft treatments to manage your mite levels. As a last resort, some may need to use a hard treatment to control their mite levels.
Using screened bottom boards and drone frames are great ways to compliment your removal of varroa mites during the spring and early summer. Screened bottom boards allow you to easily monitor mite counts by the use of a mite sheet, and also decrease mite counts by approx. 20%. Since the mites prefer the drone brood due their longer development period, adding a drone frame to your brood chamber is an easy way to additionally reduce your mite counts by approx. 20%.
If you plan to use drone frames, here's a quick review on how and when to use them. If you have an overwintered hive, they should already be on the hive. For a recently installed package hive, you should place your drone frames on the hive the first week of June.
I recommend using 1 frame per hive. Remember, using a drone frames only works if you remove the frame BEFORE the drones hatch (no more than 20-21 days after placing a drawn drone frame on the hive, slightly longer if the drone frame has not been drawn out with wax). Remove the drone frame from the hive and place in the freezer for at least 2 days to kill the drone pupae and mites. Let the frame come to room temperature and place it back in the hive. The bees will clean out the dead drones and the process can be repeated. Alternatively, you can uncap the dead drones with a capping scratcher and see all the varroa mites you have removed from your hive, which will save your bees from removing all the dead pupae.
Hope this helps! We'll be posting more information on varroa mites and the soft treatment options as the season progresses.