Behav Ecol Sociobiol (1983) 13:221-228 Behavioral Ecology and Sociobiology 9 Springer-Verlag 1983 An equilibrium theory of queen production in honeybee colonies preparing to swarm Douglas H. Baird and Thomas D. Seeley Department of Biology, Yale University, P.O. Box 6666, New Haven, Connecticut 06511, USA Received November 3, 1982 / Accepted April 25, 1983 Summary. An equilibrium model is developed which seeks to explain the regulation of queen rear- ing in honeybee colonies preparing to swarm. The model postulates that there is a balance between nurse bees becoming inhibited from queen rearing and nurses losing their inhibition, and that whether a colony does or does not rear queens reflects the equilibrium percentage of inhibited nurses. This model leads to a quantitative prediction about the size of a colony's nurse population at which queen rearing should start. Comparing the model's pre- dictions with empirical observations pinpoints data needed for a more complete explanation of control of queen rearing. In particular, the model suggests a central regulatory role for density-dependent changes in the behaviors involved in queen sub- stance dispersal. Introduction A central challenge in insect sociology is under- standing how the mass actions of colonies - such as nest construction, forage site selection, and nest thermoregulation - emerge from the meshing of individuals' behaviors (Wilson 1971). An impor- tant principle on this topic is that the actions of a whole colony often result as an overall average of the conflicting actions of its many members. For example, when an ant colony emigrates from one nest site to another, some workers stream out of the old site carrying brood to the new site, while others are busy carrying brood in the opposite di- rection, back into the old site. It is the majority of workers independently deciding to move in one direction, not some higher-level decision from a leader, which determines which site the colony eventually occupies. This 'democratic' process is perhaps most clearly demonstrated by the failure of colonies to reach a decision when their workers are divided equally between two alternatives. Such a situation was described by Lindauer (1955, 1961) in which a honeybee swarm failed to choose a home site because its scouts were attracted equally strongly to two sites in opposite directions. In this paper we explore the emergence of col- ony behavior from friendly competition among colony members through a quantitative analysis of one action of honeybee colonies: deciding whether or not to rear queens. Looking at the level of whole colonies, one observes that throughout most of the year colonies do not rear queens, but in the late spring, if a colony has grown large en- ough to swarm (i.e., bud off a daughter colony), it will rear a batch of queens, one of whom will inherit the parent colony (reviewed by Simpson 1968). Colonies also occasionally rear queens to replace senescent queens. Looking at the level of individual colony members, one observes that a colony's queen secretes large quantities of E-9-oxo- dec-2-enoic acid (queen substance) and that the queen attracts workers by other, unidentified pher- omones. One also observes that workers pick up queen substance when contacting the queen, spread it throughout the colony, and are inhibted by it from rearing queens (reviewed by Butler 1974; Michener 1974; Free 1977; see also Vierling and Renner 1977; Seeley 1979; Ferguson and Free 1980; Jugka et al. 1981). What remains unclear is exactly how to reconstruct a whole colony's de- cision-making on queen prodution in terms of the behaviors of individual colony members. In this paper we propose an hypothesis which links col- ony- and individual-level descriptions of control of queen production, and which has at its core the idea of decision-making through conflicting ac- tions.