Formation of Colony Odor in Ponerine Ant Pachycondyla apicalis

The mechanisms operating in the formation and maintenance of colony odor in the ponerine ant Pachycondyla apicalis were studied using radioactive tracers. Using [l-¹⁴C]acetate as a precursor, the de novo biosynthesis and distribution of pentane-extractable lipids within the ant's body were followed. Twenty-four hours after injection, newly synthesized alkanes, alkenes, as well as more polar lipids were found in the postpharyngeal gland, the epicuticle, and internally. Ants that had their mouths blocked with beeswax possessed significantly less radiolabeled lipids (all classes measured) in the postpharyngeal gland but had augmented levels in the internal pool and the epicuticle. Both hydrocarbons and more polar lipids were exchanged between the respective postpharyngeal glands and the epicuticle. The transfer to postpharyngeal glands was highest when both ants had an open mouth or when the recipient ant had an open mouth but the donor's mouth was blocked. This suggests that the transfer to the postpharyngeal gland in this species is by allogrooming and not by trophallaxis. Transfer to the cuticle was low and comparable in all treatments. Behavioral observations during the first 6 hr of the dyadic encounters and in intact colonies confirmed that the ants did not engage in trophallaxis. The level of transfer to the postpharyngeal gland in P. apicalis was significantly lower than in representatives of other Formicidae subfamilies studied so far. We attribute this difference to the evolution of trophallaxis in the higher Formicidae.