The individual roles of honeybee workers and drones in heat regulation were investigated using single combs of bees and brood (about 1,000 individuals) placed in boxes at 15 degrees C. After 1 h and before cluster formation, I measured the elevation of bee thoracic surface temperature (Tths) above local ambient temperature (Ta). Bees were then left overnight at 15 degrees C. During the preclustering period, the density of bees over the brood slowly increased. In the clusters left overnight, bees in the innermost layer were significantly younger than bees in the outermost layer. One-day-old bees and drones were always located in the innermost cluster layer. 89% of all workers measured had Tths - Ta greater than or equal to 2 degrees C, indicating that most workers contribute to colonial thermogenesis. Average Tths - Ta was 4.1 degrees C. Drones measured had the same average Tths - Ta as unmarked workers. Tths - Ta did not differ among bees 2 days of age and older. Location on or off the brood did not affect Tths - Ta. Cooling constants of dead bees placed near the comb in the box averaged 1.036 min-1 and were independent of location on the comb. Calculated average thoracic conductance was 0.829 cal g-1 degree C-1 min-1. Average calculated heat production per worker was 0.095 cal min-1, less than 15% of the maximal oxygen consumption of 4-day-old bees. Calculations indicate that the larger drones contribute more heat per bee than do the workers.(ABSTRACT TRUNCATED AT 250 WORDS)

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