Are multiple honeybee queen pheromones indicators for a queen-workers arms race?

Honeybees are endowed with pheromones, many of which exhibit caste specific composition, one of which is Dufour’s gland pheromone (QDP). The queen possesses long chain esters that are absent in queenright (QR) workers. However queenless (QL) workers that develop ovaries also express these queen substances. The ability of QL-workers to produce the queen-like compounds suggests that under normal conditions glandular expression is inhibited. This is corroborated by studies in vitro where Dufour’s gland detached from its normal regulation can synthesize the queen-like substances even in QR workers, indicating a role in the queenworker arms race for reproduction. QDP is only one of multiple queen specific pheromones in honeybees. A major evolutionary enigma is why the queen uses multiple signals to announce its presence, when theoretically a single pheromone should be sufficient. We hypothesize that it is the result of a pheromonal and reproductive arms race between queens and workers. Queens were selected to develop means to inhibit workers from reproducing through the production of a queen specific pheromone. Workers have counteracted not only by retaining their ability to develop ovaries, but also by retaining the capacity to produce the queen-like pheromone and by that becoming “false queens”. The next step in this evolutionary arms race was the development of a new pheromonal bouquet by the queen that was again counteracted by the worker’s ability to produce these substances. This process is facilitated because the genetic makeup of queen and workers is identical, since female larvae can develop to either caste. The result of this arms race is that queens possess multiple queen signals, only the combination of which seems to be effective. Whether this postulated arms race have reached stalemate, i.e., for each queen-pheromone there is a matched production potential in workers, or is it an ongoing arms race, i.e., a true queen-specific pheromone exists.