Wind protection

Wind protection is paramount in overwintering colonies. Colonies of bees in nature tend to seek sheltered cavities in which to build their nests, primarily to protect themselves from the chilling effect of winter winds. This was emphatically demonstrated in two seasons of testing at Madison, Wis. In each of these seasons, eight colonies of similar strength and of the same stock were selected in October. Four were overwintered in conventional wooden hives without additional protection. Top 1-in (2.5 cm) auger holes were provided. The other four were placed in hive rims with cutaway sides fitted with window screening (fig. 1). Thermocouples were placed in the interspaces of the middle frames of each hive body.

Temperatures within the clusters in both types of hives in both years were similar through January. Brood-rearing temperatures of 92° to 93° F (33° C) were recorded in all colonies, even with surrounding temperatures in the subzero range.

In one season, 2 weeks of subzero temperatures in February with high winds 20 to 30 mi/h (33 to 49 km/h) resulted in the death of all the colonies in open ventilated hives. The next season, again following a similar weather pattern, two of the open colonies were dead and two severely weakened. The four colonies in plain hives in both years were alive and in good condition.

Figure 1. -Hives with cutaway sides fitted with window screening to allow free circulation of air: Top, colonies with and without cutaway sides used in the test; Bottom, close detail.

Apparently such exposure to strong subzero wind chills the exposed bees at the cluster periphery, freezing them and causing them to drop. As the cluster erodes away in this manner, successive layers of bees are frozen, greatly weakening the colony and eventually causing its death.

Had the exposed colonies been in a quiet environment out of the wind, subzero temperatures would have been tolerated without ill effect.

Packing, Wrapping, or Cellar Wintering

The temperature inside the hive in the area not occupied by bees falls just as low as the outside temperature, whether the colony is packed or wrapped. The only difference is the rate of temperature change in the heavily packed hive is slower than in the lightly wrapped or unprotected hive. Insulation on the hive slows temperature changes within the hive. If warming periods that allow a brief cleansing flight in winter do occur, the heavily insulated colony may not be aware of the change and would fail to take advantage of a flight. For these reasons, heavy packing or insulation are not recommended. Most important considerations are the strength and condition of the bee colony, the amount and position of the honey stores, and adequate protection from the wind.

Packing or insulating beehives is costly. However, some savings in honey have been shown by packing colonies for winter. In windy locations a light tar paper wrap is valuable as a windbreak.

Colonies can be overwintered on the summer stands with no packing or wrapping if the essentials of population and quantity and position of honey stores are met. Tar paper or builders' felt may be stapled to the hives, with a hole allowed for the top entrance and the top edges folded under the hive cover to shed moisture.

When subnormal colonies are to be overwintered, cellar wintering, or its modern sequel, controlled-environment wintering, has been attempted. In the past, cellar wintering was plagued by nosema disease problems. Today, we use fumagillin to control nosema and insulate buildings or rooms.

Research is currently being conducted on controlled environment wintering. A temperature somewhere in the mid- or low-40° F (5° C) range, total darkness, ventilation to reduce excess moisture and humidity, and fall feeding of Fumidil B to suppress nosema disease are some of the major considerations. Provision for refrigeration should be considered also because sudden warming spells in late winter or early spring could result in undue restlessness and activity within the controlled-environment room. Colonies on flat-bed trailers that can be rolled outdoors or back into the room during warm or cold trends also would be desirable.

In any decision to try controlled environment wintering, serious consideration must be given to costs of the building and labor and to risks involved in holding subnormal colonies over winter. Good outdoor-wintered colonies can be divided once or twice in the spring to make needed increase.

Cause of Winter Loss

Winter loss results primarily from starvation. Starvation results from (1) lack of honey (beekeepers should leave an adequate honey reserve), (2) improper position of honey (honey reserves below or to one side of the winter cluster, rather than above it), and (3) small population (unable to cover their honey stores properly).

A small population can be the result of queenlessness, nosema infection, lack of fall brood rearing, insecticide damage in late summer, or poor colony management from overcrowding a colony with honey by inadequate supering, which restricts fall brood-rearing. In any event, the small cluster in subzero cold may cover only 2 or 3 lb (0. 9 or 1. 4 kg) of honey rather than 40 or more pounds (18. 1 kg) as is true of the large, populous colony.

A colony prevented from rearing a normal amount of brood in late summer and fall (because of crowding or queenlessness) may look populous enough in early winter. However, such a colony will be comprised mostly of older bees. They will die early in winter, which results in a small population later on. A sublethal dose of insecticide in late summer or fall may also reduce bee longevity or disrupt normal brood rearing.

Another major cause of winter loss is lack of wind protection. Colonies in exposed, windy locations will quickly become weaker because bees at the periphery chill, drop, and may eventually starve as the populations no longer can cover adequate stores.

Expected winter losses, when all requirements for good overwintering are met, should be about 1 to 3 percent of the colonies overwintered, and in many years can be nonexistent.