Winterizing Hives to Prevent Disease
We’ve been experiencing some chillier weather here in Northfield, MN the last couple of days. It was down in the 40’s as a daytime high and there were several mornings with a mild frost. Between now and mid-November is the time to start winterizing bee hives to prevent disease and starvation during colder months. Before we discuss how to winterize a hive to maximize survival, we should understand the physiology and behavior that allows bees to survive a cold winter. This will be Part 1 of a two-part series on winterizing honey bees. Part 2 will be a practical recommendation on preparing hives for cold weather.
Hive Physiology and Behavior
Bee colonies work within a yearly cycle where their behavior and physiology changes to meet the season. During the spring and summer individual bees live shorter lives, about 30 days, and all bees in the colony have specific roles that change as they age. After hatching they become nurse bees and tend brood, middle aged bees build wax, undertake and protect the colony and older bees forage for nectar and pollen. Each bee spends about 10 days in each role.
During winter months bees can live up to 240 days and they all contribute to forming a thermoregulatory cluster that keeps the colony warm and fed. During the fall “winter bees” hatch from the colony and the bees have a distinctly different physiology compared with their summer counterparts. Winter bees have increased amounts of a protein called vitellogenin, and increased hemolymph proteins, while they have a decreased amount of juvenile hormone (foraging bees have a very high amount of JH) and larger hypopharyngeal glands. It’s thought that these physiologic changes make it possible for winter bees to remain in the “nurse bee” stage which slows aging throughout the winter. Bees also rely on hormones to communicate throughout the seasons. During the winter there is little brood rearing so brood hormones don’t trigger bees to age to middle or forager status. Foraging bees also remain in the hive during the fall and release a hormone called ethyl oleate which slows down young bee maturation (Doke).
During cold months bees come together and shiver to create a thermoregulatory cluster. They use wing muscles to move air molecules and create heat, keeping it warm inside the hive. This behavior starts when air temperatures dip down below 50 degrees. The center of these clusters can be up to 95 degrees F and 40 degrees F on the outside even during the coldest parts of the winter. During honey consumption bees also produce water as a metabolic waste and the hive can become quite humid even though temperatures are below freezing outside. The bees drink the water, but it can also form dangerous condensation on the roof of the hive(Watson). The cluster of bees generally starts in the brood frames at the bottom of the hive, then moves upward into the honey supers as food is consumed throughout the winter.
There are many factors that signal to bees when to transition into winter and when to transition out again. Many of these factors have not been fully studied, but especially important among them is access to pollen, a major protein source. Colonies fed pollen at inappropriate times of the year will start to make brood and this can be detrimental to the survival of the colony. Other factors that trigger transition are presence or absence of brood, photoperiod, temperature and restriction to foraging material. There is still a lot of ongoing research in regards to successfully overwintering bees and understanding their physiology, nutritional and behavior needs.
Please stay tuned for the next post on practical recommendations for overwintering bees!
Thanks for reading and following the blog!
Dr. Eva Reinicke
Doke, M. A., Frazier, Maryann, Grozinger, Christina M. Overwintering honey bees: biology and management. Current Opinion in Insect Science. 2015, 10:185-193
Reuter, Gary S., Spivak, Marla. Wrapping Honey Bee Colony for a Northern Winter. University of Minnesota Instructional Poster #163.1, Department of Entomology.
Watson, Eliese. Winterization Guide for Beekeeping. Apiaries and Bees for Communities. http://www.backyardbees.ca