Pygidial gland secretions of Carabus Linnaeus, 1758 (Coleoptera: Carabidae): chemicals released by three species

The chemical composition of the secretions, their antibacterial activity, and the pygidial gland morphology of selected European Carabini ground beetles (Coleoptera: Carabidae)

The pygidial glands of carabids produce strong-smelling vapours. In this study, we examined the chemical composition of the gland secretions and the structure of the glands in five species of Carabini ground beetles (one species from the subtribe Calosomatina and four species from the subtribe Carabina): Calosoma (Calosoma) maderae (Fabricius, 1775), Carabus (Carabus) granulatus Linnaeus, 1758, C. (Limnocarabus) clathratus Linnaeus, 1760, C. (Carabus) ulrichii Germar, 1823, and C. (Procerus) gigas Creutzer, 1799. Additionally, we tested the antibacterial potential of the pygidial gland secretions of the two latter species against 11 bacterial strains. In order to detect the chemical content of the secretions, we used gas chromatography–mass spectrometry (GC–MS). The secretion extracts were applied against selected strains of medically important bacteria. We used bright-field microscopy to examine the morphology of the glands. We discovered a total of 11 chemical compounds in the pygidial gland extracts of the ground beetles we analysed. Ten of these compounds were identified as seven carboxylic acids, two hydrocarbons, and one aromatic aldehyde, while one chemical remained unidentified. Most of the components were isolated from the secretion of C. (L.) clathratus (nine), while the lowest number of compounds was found in C. (P.) gigas (two). Methacrylic acid was the most dominant compound by percentage in all five species, while angelic acid was also detected in all samples. As expected, salicylaldehyde was exclusively found in the species of the genus Calosoma Weber, 1801. The secretion of C. (P.) gigas was shown to achieve the highest level of antibacterial activity against Pseudomonas aeruginosa, Salmonella enterica, and S. typhimurium (even the same level as the positive control streptomycin), while the secretion of C. (C.) ulrichii achieved the highest antimicrobial potential against Staphylococcus epidermidis, S. aureus, Listeria monocytogenes, and Bacillus cereus. The most noticeable difference in the structure of the glands between the two genera is that the reservoir in Calosoma is more significantly narrowed as it leads into the efferent duct, compared to that of Carabus.

Pygidial glands of three ground beetle taxa (Insecta, Coleoptera, Carabidae): a study on their morphology and chemical composition of their secretions

Morphology of the pygidial glands and chemical compositions of their secretion were analysed in the adults of three selected ground beetle taxa. Secretions of pygidial glands of Cychrus (Cychrus) semigranosus, Patrobus atrorufus and Pterostichus (Platysma) niger were chemically tested. Additionally, pygidial glands of the latter two species were investigated using bright-field microscopy and nonlinear microscopy and morphological features of the glands were described in detail. Both C. (C.) semigranosus and P. atrorufus were studied for the first time in terms of chemical ecology, while the latter species was analysed for the first time in terms of pygidial gland morphology. Altogether, eight compounds were detected in the dichloromethane extracts of the pygidial gland secretions of the three ground beetle taxa analysed. The simplest secretion mixtures were present in C. (C.) semigranosus and P. atrorufus (with two compounds each), while the extract of P. (P.) niger contained five compounds. The presence of 1-tetradecanol in the secretion of P. (P.) niger represents the first finding of this compound from the pygidial gland secretion extracts of ground beetles.

Pygidial Glands in Carabidae, an Overview of Morphology and Chemical Secretion

Predator community structure is an important selective element shaping the evolution of prey defence traits and strategies. Carabid beetles are one of the most diverse families of Coleoptera, and their success in terrestrial ecosystems is related to considerable morphological, physiological, and behavioural adaptations that provide protection against predators. Their most common form of defence is the chemical secretion from paired abdominal pygidial glands that produce a heterogeneous set of carboxylic acids, quinones, hydrocarbons, phenols, aldehydes, and esters. This review attempts to update and summarise what is known about the pygidial glands, with particular reference to the morphology of the glands and the biological function of the secretions.

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

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.