Condition-dependent timing of comb construction by honeybee colonies: How do workers know when to start building?

Colonies of honeybees, Apis mellifera, initiate new comb construction only when two conditions are met: (1) they are currently collecting nectar and (2) they have filled their available comb beyond a threshold level with brood and food. In this study I explored how the individual workers responsible for building might use readily accessible local cues to acquire this global information on colony and environmental state. In particular, I tested the hypothesis that comb is built by nectar receivers (bees specialized to receive nectar from foragers and store it in Comb cells) that experience increased distension of their crops, crop distension could serve as a cue that both conditions for building have been satisfied, because the bees' crops will fill up as they receive nectar from successful foragers and have difficulty finding comb in which to store it. However, two findings led to rejection of this hypothesis. First, very few nectar receivers participated in comb building. Most builders came from another, unidentified subpopulation of workers. Second, potential builders showed no increase in crop size correlated with the onset of new comb construction or with the development of conditions that favour comb building. This was true both for identified nectar receiver bees and for bees belonging to the age cohort at which wax secretion and comb building reach their peak levels. The behavioural repertoire of comb-building bees suggests that these builders come from a pool of underemployed bees that may evaluate colony state by direct inspection of comb cells.