The sophisticated organization of eusocial insect societies is largely based on the regulation of complex behaviors by hydrocarbon pheromones present on the cuticle. We used electrophysiology to investigate the detection of cuticular hydrocarbons (CHCs) by female-specific olfactory sensilla basiconica on the antenna of Camponotus floridanus ants through the utilization of one of the largest family of odorant receptors characterized so far in insects. These sensilla, each of which contains multiple olfactory receptor neurons, are differentially sensitive to CHCs and allow them to be classified into three broad groups that collectively detect every hydrocarbon tested, including queen and worker-enriched CHCs. This broad-spectrum sensitivity is conserved in a related species, Camponotus laevigatus, allowing these ants to detect CHCs from both nestmates and non-nestmates. Behavioral assays demonstrate that these ants are excellent at discriminating CHCs detected by the antenna, including enantiomers of a candidate queen pheromone that regulates the reproductive division of labor.

Background: Mutual policing is an important mechanism for reducing conflict in cooperative groups. In societies of ants, bees, and wasps, mutual policing of worker reproduction can evolve when workers are more closely related to the queen's sons than to the sons of workers or when the costs of worker reproduction lower the inclusive fitness of workers. During colony growth, relatedness within the colony remains the same, but the costs of worker reproduction may change. The costs of worker reproduction are predicted to be greatest in incipient colonies. If the costs associated with worker reproduction outweigh the individual direct benefits to workers, policing mechanisms as found in larger colonies may be absent in incipient colonies.

Results: We investigated policing behavior across colony growth in the ant 'Camponotus floridanus.' In large colonies of this species, worker reproduction is policed by the destruction of worker-laid eggs. We found workers from incipient colonies do not exhibit policing behavior, and instead tolerate all conspecific eggs. The change in policing behavior is consistent with changes in egg surface hydrocarbons, which provide the informational basis for policing; eggs laid by queens from incipient colonies lack the characteristic hydrocarbons on the surface of eggs laid by queens from large colonies, making them chemically indistinguishable from worker-laid eggs. We also tested the response to fertility information in the context of queen tolerance. Workers from incipient colonies attacked foreign queens from large colonies; whereas workers from large colonies tolerated such queens. Workers from both incipient and large colonies attacked foreign queens from incipient colonies.

Conclusions: Our results provide novel insights into the regulation of worker reproduction in social insects at both the proximate and ultimate levels. At the proximate level, our results show that mechanisms of social regulation, such as the response to fertility signals, change dramatically over a colony's life cycle. At the ultimate level, our results emphasize the importance of factors besides relatedness in predicting the level of conflict within a colony. Our results also suggest policing may not be an important regulatory force at every stage of colony development. Changes relating to the life cycle of the colony are sufficient to account for major differences in social regulation in an insect colony. Mechanisms of conflict mediation observed in one phase of a social group's development cannot be generalized to all stages.