Chemistry and morphology of the pygidial glands in four Pterostichini ground beetle taxa (Coleoptera: Carabidae: Pterostichinae)

Abstract

Morphology of the pygidial glands and chemical composition of their secretions in adults of four ground beetle representatives of the Pterostichini tribe (Coleoptera: Carabidae) were analysed. Molops (Stenochoromus) montenegrinus, Pterostichus (Cophosus) cylindricus, P. (Feronidius) melas and P. (Pseudomaseus) nigrita were chemically tested, while the latter three species were morphologically investigated. Pterostichus (C.) cylindricus, P. (P.) nigrita and M. (S.) montenegrinus were chemically studied for the first time. Altogether, 23 chemical compounds were isolated using gas chromatography-mass spectrometry (GC-MS), of which some are new for Pterostichini or even Carabidae. Methacrylic acid was present in all species analysed. It was predominant in the secretion extract of P. (C.) cylindricus and P. (F.) melas. Isobutyric and 2-methylbutyric acids were the major components in the secretion of M. (S.) montenegrinus. Undecane, methacrylic and tiglic acids were the main components in the secretion of P. (P.) nigrita. The simplest chemical mixture was found in P. (C.) cylindricus (two compounds), while the most complex one was detected in P. (P.) nigrita (15 compounds). No significant differences in the chemical composition of the pygidial gland secretions were evidenced in P. (C.) cylindricus sampled from the same area and in the same season in two different years. Morphology of the pygidial glands of the studied species was analysed for the first time. Morphological features of the pygidial glands were observed using bright-field microscopy and nonlinear microscopy and described in details.