Colony takeover by a socially parasitic ant, Polyergus breviceps: the role of chemicals obtained during host-queen killing

Abstract

Abstract. The behavioural adaptations of parasitic ant queens are more complex than those of parasitic birds, in which the egg-laying female approaches the nest only when the host parents are absent, and leaves immediately after egg deposition. Queens of the socially parasitic ant Polyergus breviceps are incapable of rearing their own brood, and therefore require the assistance of host Formica workers soon after egg laying. Accordingly, a newly mated Polyergus queen must penetrate a nest of Formica, kill the host queen, and become permanently accepted by the slave species' workers. Laboratory tests show that a Polyergus queen will similarly attack and bite a dead (and therefore motionless) Formica queen. Immediately after attacking the dead host queen, the Polyergus queen will be accepted by workers from any colony of Formica belonging to the same species of the dead queen (but will be attacked by workers from other Formica species). Preliminary results also indicate that any adoption-facilitating chemicals obtained by the Polyergus queen are still effective 1 week after killing the host Formica queen. When Polyergus queens raised in colonies containing F. gnava were introduced into nests of F. occulta, most showed little interest in attacking the resident Formica queen. In four of 10 tests, however, the Polyergus queen killed the foreign queen and was accepted by the F. occulta workers. Such chemical transfer of foreign-queen odours may have played a key role in the evolution of social parasitism in Polyergus.