Chemical ecology and social parasitism in ants

The chemical strategies by which parasites manage to break into the social fortresses of ants offer a fascinating theme in chemical ecology. Semiochem icals used for interindividual nestmate recognition are also involved in th e mechanisms of tolerance and association between the species, and social p arasites exploit these mechanisms. The obligate parasites are odorless ("ch emical insignificance") at the time of usurpation, like all other callow an ts, and this "invisibility" enables their entry into the host colony. By ch emical mimicry (sensu late), they later integrate the gestalt odor of this colony ("chemical integration"). We hypothesize that host and parasite are likely to be related chemically, thereby facilitating the necessary mimicry to permit bypassing the colony odor barrier. We also review the plethora o f chemical weapons used by social parasites (propaganda, appeasement, and/o r repellent substances), particularly during the usurpation period, when th e young mated parasite queen synthesizes these chemicals before usurpation and ceases such biosynthesis afterwards. We discuss evolutionary trends tha t may have led to social parasitism, focusing on the question of whether sl ave-making ants and their host species are expected to engage in a coevolut ionary arms race.