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 pro vides 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 comprehensi ve analysis of metapleural gland secretions of Acromyrmex oetospinosus, usi ng a recently developed method for the analysis of polar compounds by gas c hromatography and mass spectrometry. We show that the chemical identity and quantitative recovery of different compounds in the metapleural gland secr etion depends upon the method used and the type of colony from which the sa mples are taken. In addition to the two compounds previously recorded in th e metapleural gland secretion of Acromyrmex ants (indolacetic acid and myrm icacin), 20 new compounds were detected in the secretion of a random sample of workers from two laboratory colonies and two held colonies. These compo unds 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 discuss ed.