Chemical secretion and morpho-histology of the pygidial glands in two Palaearctic predatory ground beetle species: Carabus (Tomocarabus) convexus and C. (Procrustes) coriaceus (Coleoptera: Carabidae)

Although all ground beetles have pygidial glands homologous in structure and function, there are many differences among species, often significant, in terms of chemical composition of the secretion and morphology of the gland components. In this paper, two predatory ground beetle species of the genus Carabus, namely C. (Tomocarabus) convexus and C. (Procrustes) coriaceus, were subjected to chemical, morphological and histological study of their pygidial glands and the glands' secretions. Altogether, three carboxylic acids were isolated, and the pygidial gland reservoir and other glandular parts are morphologically described in the study. We also tested whether there exist differences in chemical content of the secretion obtained by upsetting the beetles in a traditional way and that obtained directly from intact reservoirs. Detailed data on morphology of the pygidial glands of both species are presented, as well as updated information about the chemical components of the glandular secretions. Apart from tiglic and methacrylic acids, which are typical for Carabus pygidial secretions, we also found benzoic acid as a minor component of the secretion in both species. In addition, a chemotaxonomic overview of Carabus taxa is given in the paper.