Impact of Bad Weather on the Development of the Broodnest and Pollen Stores in a Honeybee Colony (Hymenoptera: Apidae)

Abstract

A honeybee colony of the race Apis mellifera carnica Pollmann 1879 with about 12.300-13.100 individuals, housed in an eight-frame observation hive (2 x 4 vertically arranged frames), was observed in summer 1997. The amounts of food stores and brood were measured during alternating periods of good weather (3 periods of 6 days each) and bad weather (3 periods of 5 days each), which was simulated by intense artificial rain. The amount of stored pollen typically increased during periods of good weather and decreased during phases of bad weather. The honey reserves were plentiful during the entire experiment. The larvae were classified into 2 categories according to their size: 'small' larvae (estimated fresh weight 140 mg). The total number of larvae increased slightly and fairly consistently over the course of the whole study, but under different weather conditions there were significant differences in the amounts of small and large larvae. During bad weather periods, the number of large larvae decreased significantly and heavily, while the number of small larvae increased. In contrast, during good weather conditions, the number of large larvae significantly increased, and the number of small larvae did not change. The changes in the number of large larvae correlated well with the changes in the amount of pollen in the colony. It seems that, during bad weather, a decline in the pollen stores might alter the brood-feeding behaviour of nurse bees, and this can result in underfed larvae, which may be sealed at a lighter weight. As the decreases in the number of large larvae started early in the rainy period, when pollen was still available, the bees seem to switch very rapidly to a 'save resources' strategy when a period of lack arises. The results do not suggest that brood cannibalism was prevalent, although this behaviour is known to occur under bad weather conditions.