Metaplural gland secretion of the leaf-cutter ant Acromyrmex octospinosus:: New compounds and their functional significance

Ants of the myrmicine tribe Attini live in symbiosis with a fungus that provides them with food. In return the ants maintain optimal growth conditions fur the fungus, weed out competing microorganisms, and inhibit the growth conditions of these competitors by chemical means. We present a comprehensive analysis of metapleural gland secretions of Acromyrmex oetospinosus, 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 held colonies. These compounds span the whole range of carboxylic 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.