Comparative morphology of abdominal glands in Paederinae (Coleoptera : Staphylinidae)

Abstract

Glandular structures at the sternites of 31 species of Paederinae (Coleoptera : Staphylinidae) are described in detail for the first time. A median gland of unknown biological significance is situated at the front margin of the 4th sternite in Paederus and Paederidus ( Paederus s.l.). A gland tissue at the posterior border of the antecosta opens into a reservoir situated between the antecosta and the intersegmental membrane. Each of the numerous glandular units obviously consist of 2 secretory cells that are drained by a tubule. They are thus related to dermal glands. Two types of pores, single pores and pore plates, are dispersed over the body, but are aggregated in the vicinity of the aperture of the reservoir. In Rugilus, 2 hitherto unknown glands of the same shape are located at the front margins of sternites 4 and 5. In contrast to the glands of Paederus s.l., there are big pores under the gland tissue and the opening area lies in a pit. One further species, Stilicosoma rufipes, was recently classified in the genus Rugilus, but does not have any glands, and therefore the genus Stilicosoma Casey, which was once named for S. rufipes, is re-established. Ochthephilum fracticorne does not have a reservoir, but otherwise combines features of both the glands of Paederus s. l. and those of Rugilus. This link points out the possible derivation of these glands from a common origin. All species of Lathrobiina have accumulations of tubules at the front margins of at least the 4th sternites, and thus represent a rather primitive stage in the development of the glands, while the lack of glandular peculiarities at the 4th sternites in Medonina is plesiomorphic. With respect to a special type of dermal tubules, the genera Medon, Pseudomedon, and Sunius are distinguished from Lithocharis, hence denoting a clear dividing line between the subtribes Medonina and Lithocharina. These features as well as the glands themselves, provide the basis for clarifying the largely unknown phylogeny of Paederinae.