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Chemistry and morphology of the tergal gland of freeliving adult Aleocharinae (Coleoptera: Staphylinidae) and its phylogenetic significance

Abstract. Morphology and chemistry of the tergal gland, an abdominal defensive gland of the Staphylinidae subfamily Aleocharinae, is studied comparatively in twenty‐two species of ten Central European tribes. To determine trends in the morphological evolution of the tergal gland the results are compared with well‐known evolutionary trends of gland systems of other insects. The possible chemical evolution of the gland secretion is proposed by considering the biosynthesis of the different secretion compounds and by testing their biological efficiency on Calliphora larvae (irritancy, mortality). The morphological evolution probably proceeded from a small reservoir with only a few glandular cells D1 (primitive) to a large and bilobed reservoir with a great number of glandular cells D1 (advanced). In the chemistry of the quinone‐containing gland secretion, long‐chain fatty acids as solvents in primitive species were probably replaced by short‐chain fatty acids (derived condition). Most advanced species also use hydrocarbons and aldehydes as solvents. With reference to these results, both a statistical (Jaccard‐coefficient) and a cladistic analysis are performed to test previous ideas on the phylogeny of the Aleocharinae.