2Department of Chemistry and Chemical Biology

Abstract—Analyses of pygidial gland contents of two species of a previously uninvestigated family of beetles (Trachypachidae) by Gas Chromatography-Mass Spectrometry (GC-MS) revealed that their chemistry is similar to that reported from many members of the family Carabidae. Nevertheless, the com-position of defensive gland fluids of the two species Trachypachus slevini and T. gibbsii differs sufficiently to distinguish between the two species solely on the basis of their defensive chemistry. The major components of T. slevini glandular fluid are methacrylic, tiglic, and octanoic (D caprylic) acids, together with the hydrocarbon (Z)-9-pentacosene. In contrast, the glandular contents of T. gibbsii contain a rather unique mixture of polar and nonpolar compounds, the princi-pal constituents of which are methacrylic and ethacrylic acids (D 2-ethylacrylic acid), together with 2-phenylethanol, 2-phenylethyl methacrylate, 2-phenylethyl ethacrylate, and (Z)-9-pentacosene. Key Words—Defensive secretion, methacrylic acid, tiglic acid, octanoic acid, Trachypachidae, Trachypachus slevini, Trachypachus gibbsii