New results in the defensive chemistry of Crematogaster ants

Ants of the genus Crematogaster are able to raise their abdomen forwards and over the thorax and head. In many Crematogaster species, the venom is emitted as a froth that accumulates on the spatulate portion and at the basis of the sting, and thus can be easily applied to the integument of enemies. In the three European species of Crematogaster ants, the Dufour gland contains complex mixtures of long chain derivatives bearing a (E,E)-cross-conjugated dienone linked to a primary acetate function. When the venom is emitted, these compounds are transformed into highly electrophilic and toxic 4-oxo-2,5-dienals by an esterase and an oxidase stored in the poison gland. On the other hand, the Dufour gland of one Crematogaster species from Papua-New Guinea produces long chain furan derivatives, whereas two Brazilian species produce furanocembrene diterpenes. To further investigate the defensive mechanisms in this genus and to assess whether the composition of the Dufour gland secretion could be used for taxonomic purposes, we have now studied two other Crematogaster species. The Dufour gland of C. nigriceps from Africa contains a mixture of l-alkyl-l,3,5-cyclohexanetriols. In C. montezumia, collected in Argentina, the defensive mechanism is based on the production of triacylglycerols bearing polyunsaturated fatty acids containing (Z,Z,Z)-conjugated trienes or (5E,8Z,10Z,12Z)-tetraenes, which are responsible for the strong sticking properties of the secretion.