Solar heating of honey bee colonies (Apis mellifera L.) during the subtropical winter and its impact on hive temperature, worker population and honey production

We studied the impact of solar heating of bee colonies by placing beehives inside Infrared-Polyethylene (PE) covered enclosures, on: hive temperature, bee population, and spring honey production, during the subtropical winter (December 2000-March 2001) in Israel's Coastal Plain. During this period, the ambient daily maximum temperature fluctuated between 12.8 and 23.1degreesC. Out of the 1192 light hours, only 90 hours were cloudy and cold (<8degreesC). The precipitation was 176.8 mm rain, and the average wind velocity was 1.5 m/sec, above the threshold of bee foraging activities. The temperature inside empty, non-covered hives was close to the ambient It at 40 cm above the ground. However, on a bright day and clear night the It inside empty, PE-covered hive was higher by 12.2 and 1.7degreesC, respectively, than that inside an empty, non-covered hive. The degreest inside an empty, PE-covered hive resembled that inside PE tunnels and greenhouses, reaching maximum and minimum values during the noon and in the early morning, respectively. At all measuring positions, the It was always higher in PE-covered colonies than in non-covered ones. The temperature outside the brood area in PE-covered hive was higher by 9.3 and 2.7degreesC during a bright day and clear night, respectively, than in non-covered ones. The brood area degreest ranged between 34.8 and 36degreesC Brood area size in PE-covered hives increased by 59.2% (+2290 cm(2)) during the experimental period, but it went down by 8.4% (-504 cm(2)) in non-covered hives (P=0.05). Adult bee population in PE-covered hives increased by 37.5% (3.8 occupied frames) during the winter, versus only 11.8% (1.8 occupied frames) in non-covered hives. During the spring, PE-covered colonies produced +/-20.8 kg honey/colony, while non-covered colonies produced only +/-10.2 kg honey/colony (P=0.0004). We demonstrated that the temperature that prevailed in PE-covered populated hives was higher than non-covered ones, and resulted in a faster increase of the brood area size, colony population build-up and more spring honey per colony.