Pollen utilization in non-breeding honeybees in winter

Abstract During the broodless period in winter, the pollen content of the gastrointestinal tract, the degree of pollen digestion and the proteolytic activity in the midgut were investigated in bees from the margin and from the centre of clusters of two colonies of Apis mellifera L. in Austria. In addition, the movement of bees within the winter cluster was examined. There was no difference in pollen content and proteolytic activity between bees from the centre or margin of the cluster, nor did the 2 groups show a preference for staying at the centre or on the margin of the winter cluster. Compared to 8–9-day-old bees in summer, the amount of pollen in the midguts was smaller by a factor of 100–1000, but the degree of pollen digestion in the midgut and the rectum was significantly greater; the proteolytic activity in the midgut was approximately a quarter. The more efficient utilization in spite of lower proteolytic activity might be due to pollen staying longer in the midgut. Foragers in summer also consume only minimal amounts of pollen but have a smaller degree of utilization than winter bees. The reduced pollen consumption rate, and efficient utilization in spite of lower proteolytic activity are useful adaptations to the reduced availability of pollen and reduced protein metabolism which bees experience during the winter.