Colony Founding by Queens of the Obligatory Slave‐making Ant, Polyergus breviceps: The Role of the Dufour's Gland1

We conducted laboratory studies of the process by which newly‐mated queens of the slave‐making ant Polyergus breviceps invade colonies of their host species Formica gnava, kill the resident Formica queen, and appropriate the brood. The aggressive behavior of resident Formica workers towards the invading Polyergus queen subsides shortly after the Formica queen is killed. To elucidate the chemical basis for the reduction in aggression, we prepared extracts of Dufour's, pygidial, and poison glands from Polyergus queens. Workers of the harvester ant Pogonomyrmex occidentalis were daubed with these extracts, and introduced into dishes containing Formica workers. Only the Dufour's secretion protected the intruding ants from incessant aggression by Formica. Preliminary studies also show that the enlarged, bilobed Dufour's gland of the Polyergus queen decreases in size shortly after mating, when developing oocytes occupy a significant portion of the queen's gaster.