Repellent effect on host Formica workers of queen Dufour's gland secretion of the obligatory social parasite ant, Polyergus samurai (Hymenoptera: Formicidae)

Founding queens of the obligatory social parasite ant Polyergus samurai usurp the host Formica japonica colony. The queen secretes chemicals from its gaster when killing the host queen. At this time, the parasite queen is hardly attacked by host workers. We hypothesized that the queen's secretion acts as a repellent to deter host workers' aggression during host queen killing. Gas chromatograph-mass spectrometry analyses confirmed that the chemical composition of Dufour's gland contents of P samurai queens was almost identical to the chemicals remaining on the body surface of host Formica queens killed by them. Host F. japonica workers were used for bioassays. In an encounter with an intruder ant, the workers' aggression to the intruder was reduced significantly when Dufour's gland extract was applied to the intruder. Treatment of workers with the gland extract significantly increased the receding behavior of nest-mates. The host workers receded from a glass dummy treated with the gland extract. The time necessary for a worker to get over a barricade applied with gland extract was significantly longer than that of controls. These results strongly suggest that Dufour's gland secretion acts as a repellent allomone.