Colony founding in Polyergus rufescens: the role of the Dufour's gland

In the European slave-making ant Polyergus rufescens, the occurrence of chemical strategies during the initial phase of dependent colony foundation or usurpation was investigated. To test this idea, we analysed the effect of the secretion of different glands (Dufour's, poison, pygidial, rectal, and mandibular) on the behaviour of workers of its common host species, Formica cuniculavia (subgenus Serviformica). Workers of another species, Formica rufibarbis (Serviformica), were daubed with these extracts, and introduced into colony fragments of F. cuniculavia. The results of a set of laboratory aggression test showed that the secretion of the mandibular, pygidial, rectal, and poison glands do not alter the characteristic aggressive reactions generally performed by resident workers against alien ants. By contrast, the Dufour's gland seems to play a crucial role in the appeasement of residents of the target host colony. In fact, its secretion drastically lowers the degree of overt attacks shown by F. cunicularia workers against the intruders. This chemical strategy probably allows an easier invasion and usurpation of host colonies by newly mated females of P. rufescens.