Nesting Behavior and the Evolution of Worker Tempo in Four Honey Bee Species

Three Asian honey bee species (Apis florea, A. cerana, and A. dorsata) were studied in Thailand, and compared with the European honey bee A. mellifera, to explore the energy implications of interspecific differences in worker body size and nesting behavior. From previous work on these four species, we know that several measures of the energy—related performance of foragers (body temperature, flight speed, wing loading, and mass—specific metabolic rate) deviate from predicted size—dependent patterns. Instead, workers in the two species intermediate in body size, A. cerana and A. mellifera, appear to be high—powered relative to those of the largest species (A. dorsata) and the smallest species (A. florea). Among the Asian species, A. cerana's colonies also show a disproportionately high mass—specific metabolic rate, and their foragers make many more trips per day in the same habitat than do foragers of the other species. These various traits seem to be functionally related, and to represent evolved differences among species in worker "tempo," i.e., in the rate of performance of colony tasks. Correlated with the dichotomy in worker tempo is a dichotomy in nest architecture and intracolony demography. The low—tempo species (Apis florea and A. dorsata) nest in the open, protecting the comb and its contents with a thick curtain of young worker bees. The high—tempo species build their nests in enclosed cavities, which allows the workers to protect and provision a relatively larger area of comb. Worker life—span is longer in the open—nesting species; this allows colonies to maintain the work force needed for the curtain, even though the rate of worker production (per capita) is lower than that of cavity nesters because of the relatively small number of brood cells available. With the assumption that there is a fundamental relationship across species among tempo, foraging performance, and the rate of mortality, we propose that the relatively high tempo of cavity—nesting workers has been favored for two reasons. First, a benefit of higher tempo (enhanced ability to provision brood) is better realized owing to the greater brood—rearing capacity of their nests. Second, a cost of higher tempo (shorter life—span, resulting in fewer workers available for nest production) is less important for the cavity nesters because the cavity walls reduce the need for protection by workers.