By Jason A. Long, M.S. Student, Washington State University
Overwintering honey bee colonies is a common practice, with both outdoor wintering and indoor wintering conducted. Colonies heading into winter produce special winter bees. Winter bees, compared to summer bees, have enlarged fat bodies and pharyngeal glands, high levels of protein, and low levels of juvenile hormone. Winter bees live for 100 plus days, compared to 20 to 40 for summer bees. Overwintering bees cluster together as temperature drops and control temperature within the cluster via endothermic heat production by shivering of wing muscles and by increasing density of the cluster to better hold in heat.
Indoor wintering provides an ability to control environmental temperature, limiting the fluctuations seen in outdoor wintering, reducing food consumption, and protecting hives from weather and animals. Indoor wintering has the drawback of not allowing bees cleansing flights on warmer days, reduces brood reared and requires active ventilation.
Over the winter of 2011-2012 , Washington beekeeper Eric Olson wintered his bees indoors in Yakima, WA and high carbon dioxide levels were observed. This led to a literature search and discovery of prior research by Karel Van Nerum and Herman Buelens on metabolic rates and oxygen/carbon dioxide levels in wintering hives. They found that internal oxygen levels in clusters naturally decreased to levels as low as 15%, and carbon dioxide levels went as high as 6%. As the ambient oxygen approached the 15% level, there was reduced metabolic activity within the cluster.
In my research, I will compare two commercial indoor wintering setups (Eric Olson in Yakima, Washington and Tom Hamilton in Nampa, Idaho) with outdoor control colonies located at their sites. In Pullman, Washington I will conduct controlled atmosphere testing, and compare varying levels of oxygen and carbon dioxide against normal background atmospheric levels. I anticipate that my research will provide insight into improved methods for indoor wintering that may increase survivability and reduce food consumption in wintering bees.