2. Effects of the Removal of Insulation on Colony Temperatures
Manuscript Received for Publication March 14, 1989

by TIBOR I. SZABO
Agriculture Canada Research Station
Box 29, Beaverlodge, Alberta, Canada T0H 0C0


SUMMARY

Temperatures within the SW hive of each of four 4-colony wintering packs were recorded before and after removal of insulation at 6 h intervals from the 17 to 19 May, 1983. The insulation packs were removed on 18 May at 11.00 h. Prior to removal of the insulation the temperatures throughout the honey bee clusters were nearly constant. Within 3 to 24 h after removal of the insulation, temperatures decreased on the outer sides of all colony clusters.

INTRODUCTION

On the Canadian prairies outdoor wintering colonies are packed with insulation and weatherproof covers, usually in groups of four (Szabo, 1974, 1980, 1983 and 1985). The insulation remains on the colonies from approximately the middle of October until early April or May. If the colonies are not provisioned with enough food, early spring feeding is necessary. The wintering pack must be opened to permit the use of the common 9 l feederpails. Some beekeepers remove the wintering pack while others remove only the top insulation, replacing it again after the feeding period. By mid-May the population in many colonies is so large that the provision of extra hive bodies with combs, or 'supering' becomes essential. This procedure is usually preceded by the final removal of the wintering packs, the cleaning of the bottom boards and the closure of the top entrance of each hive. The hives are also spaced 10 to 50 cm apart. The effects of the removal of the wintering packs on cluster temperatures were investigated in this study.

MATERIALS AND METHODS

Sixteen honey-bee colonies of Alberta Bee breeding stock, were wintered in standard Langstroth hives at Beaverlodge, Alberta, 55.1ºN, 119.2ºW. In August, 1982, after the honey flow, these colonies were restricted to two brood chambers. Each colony contained an estimated 5 kg of bees. During September the colonies were fed with 9 l of sugar syrup (60%) containing 200 mg of fumagillin. Then sugar syrup was supplied until each colony without a hive cover, reached a total weight of 64 kg.

Bottom and top entrances (each 1 x 5 cm) were provided on the front of each hive. At the end of October, groups of 4 colonies were packed tightly together. In each group two colonies faced north and two colonies faced south. The groups were covered with R12 fiberglass insulation and building paper on the sides and R24 fiberglass insulation on the top. The top fiberglass was covered with a 1 cm thick 122 x 122 cm sheet of plywood. The plywood, paper and fiberglass were secured with baler twine. The hive bottoms were not insulated. Entrance holes were cut through the building paper and fiberglass, in line with the upper entrance holes of the hives. Colored plywood pieces (10 x 15 x 0.8 cm) with approximately 2 x 6 cm openings were nailed to the top entrances.

The SW colony in each of the 4 packs was equipped with remote temperature sensing thermistors. Each hive body contained 10 combs and the thermistors were placed between the 2nd and 3rd, the 5th and 6th, and the 8th and 9th combs in both hive bodies. In each SW hive there was a total of 54 thermistors attached to 6 combs. There were 3 rows of 3 thermistors in each comb, making a rectangle pattern with 7 cm between adjacent thermistors in rows and 14.3 cm in columns. The first row of 3 thermistors was 3.2 cm from the top bar of the frame. The thermistors were connected with shielded cables to two CR5 Digital Recorders (Campbell Scientific Inc.), located in the apiculture laboratory. Ambient temperature was measured with thermistors in a Stevenson screen placed west of the four colonies. All thermistors were checked prior to installation at 5 [41.0ºF], 10 [50.0ºF], 20 [68.0ºF], 30 [86.0ºF] and 35ºC [95.0ºF] and those indicating a deviation of more than 0.5º [32.9ºF] were replaced. The thermistors were installed during August to minimize disturbance to the colonies.

The hive and ambient temperatures were recorded on 17 May 1983 at 20.00 h MDT and on 18 May at 2.00 and 8.00 h. On May 18 at 11.00 h packing was removed and the hives spaced 20 to 50 cm apart. Top entrances were closed and covers equipped with R5 styrofoam insulation were installed on each hive. Temperatures were recorded again at 14.00 and 20.00 h and on 19 May at 2.00, 8.00 and 14.00 h.

The recorded data was tabulated and the 10 [50.0ºF], 20 [68.0ºF] and 30ºC [86.0ºF] isotherms in the three cross sections of the hives were fitted among the data points by eye. The 10º [50.0ºF] isotherms were connected between the cross sections to delineate the approximate size of the wintering cluster. The space of the 30º [86.0ºF] temperature area was dotted. In each cross section the highest and lowest rounded temperatures were recorded. Temperature records for each of the four hives were recorded and plotted separately and no attempt at statistical averaging was made.

Fig. 1. Isotherms of the 10 [50.0ºF] (dotted line) 20 [68.0ºF] (broken line) and 30º [86.0ºF] (solid line) temperatures in three cross sections of the insulated hives and honeybee colonies on 17 May at 20.00 h and 18 May, 1983 at 2.00, 8.00 and 14.00 h. The Insulation packs were removed on 18 May at 11.00 h. In each cross section the minimum and maximum temperatures are also recorded. The dotted area represents the 30º [86.0ºF] and higher temperatures. The ambient temperature is marked below the hive drawings. Each hive drawing represents the SW hive from a 4-colony pack.

Fig. 2. Hive and colony temperatures on 18 May at 20.00 h and 19 May, 1983 at 2.00, 8.00 and 14.00 h. See notes to Fig. 1.


RESULTS AND DISCUSSION

Three dimensional drawings of isotherms of the four colonies at specified times before and after removal of the insulating wintering pack are presented in Figs. 1 and 2. Colony No. 3 which initially had the smallest cluster was the first to respond. Within three hours of removal of insulation temperatures at the outer side of the colony dropped dramatically. Six hours later colonies 1 and 2 showed a drop in temperatures on their outer edges, and by 8.00 h the next day all four colonies registered lower temperatures on their outer boundaries, indicating that the clusters had contracted to the central portion of each colony despite relatively high ambient temperatures of 7.7 [45.86ºF] to 19.3ºC [66.74ºF].

Owens (1971) demonstrated that the temperature at the outer edge of the cluster was 6.7º [44.06ºF]. The bees on the outer edge face into the cluster, and this temperature was measured at the abdomen of the outermost bees. He found that the bees were densest just inside this outer edge, where the temperature was 12.8º [55.04ºF] to 13.3º [55.94ºF]. The mean of these temperatures was 10º [50.0ºF] and was chosen as the isotherm marking-position of the honey-bee colony cluster in the wintering hives in the present study. Owens (1971) also showed that when brood was on one side of a thermocouple, the temperature was 29.4º [84.92ºF] to 33.3º [91.94ºF] depending on the stage of brood and temperatures of 33.3º [91.94ºF] to 34.4º [93.92ºF] were recorded at all locations where brood was on both sides of the thermocouple. The isotherm of 30º [86.0ºF] was thus marked as locating possible brood area in the present paper. This temperature disappeared from one whole cross section of colonies 1, 2 and 3 by 19 May and greatly reduced in colony 4.

In wintering colonies brood is often found on the inner (adjacent) sides of the colonies where temperatures tend to be maintained at a somewhat higher level. It is therefore suggested that in order to minimize spring temperature shock and to encourage maximum brood development in wintered colonies, the removal of the insulation from the wintered packs be delayed as long as practically possible. The reluctance of beekeepers to unpack the colonies too early is therefore fully justified.


ACKNOWLEDGEMENTS

Paul van Westendorp drew the illustrations and provided technical assistance during the study. The research was partially supported by Farming for the Future, Agricultural Research Council of Alberta.


REFERENCES

Owens, C. D. (1971) The thermology of wintering honeybee colonies. Tech. Bull. U.S. Dep. Agric. No. 1429.

Szabo, T. I. (1974) Outdoor wintering of honey bee colonies in the Nipawin area of Saskatchewan. Can. Beekeeping (12):89-91.

Szabo, T. I. (1980) Outdoor wintering of Italian and Caucasian-Italian hybrid honey bees. Am. Bee J. 120(7):513, 514 and 517.

Szabo, T. I. (1983) Effects of various entrances and hive direction on outdoor wintering of honey bee colonies. Am. Bee J. 123(1):47-49.

Szabo, T. I. (1985) The thermology of wintering honeybee colonies in 4-colony packs as affected by various hive entrances. J. Apic. Res. 24:27-37.