1Chemical Ecology Group, Keele University , Keele, Staffordshire, ST5 5BG, England.
2University of Aarhus, Ny Munkegade, building 540, 8000 Aarhus C, Denmark.
3University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark.
Ants of the myrmicine tribe Attini live in symbiosis with a fungus which provides them with food. In return the ants maintain optimal growth conditions for the fungus, weed out competing microorganisms and inhibit the growth conditions of these competitors by chemical means. The secretion of the metapleural gland of attine ants has been hypothesized to be important for protection against infections and proper maintainance of the fungus garden. However, to date only a few compounds have been identified in the metapleural gland secretion because of difficulties in analysing these highly polar mixtures. Here we present a comprehensive analysis of metapleural gland secretions of Acromyrmex octospinosus using a recently developed method for the analysis of polar compounds by gas chromatography and mass spectrometry. We show that the chemical identity and quantitative recovery of different compounds in the metapleural gland secretion depends upon the method used and the type of colony from which the samples are taken. In addition to the two compounds previously recorded in the metapleural gland secretion of Acromyrmex ants (indolacetic acid and myrmicacin) 20 new compounds were detected in the secretion of a random sample of workers from two laboratory colonies and two field colonies. These compounds span the whole range of carbon acids from acetic acid to the long chain fatty acids, but comprise also some alcohols, lactones and keto-acids. The possible function of this highly complex secretion mixture is discussed.