Astenus DEJEAN 1833

Assing, V., 2008, On the taxonomy and zoogeography of some Palaearctic Paederinae and Xantholinini (Coleoptera: Staphylinidae), Linzer biologische Beiträge 40 (2), pp. 1237-1294 : 1240-1241

3.1.1. Astenus DEJEAN 1833

On the subgenus Astenognathus REITTER 1909

The subgenus Astenognathus was described by REITTER (1909) to include seven species, among them A. bimaculatus (ERICHSON) , which was subsequently designated as the type species by BLACKWELDER (1939). According to REITTER (1909) and later authors, Astenognathus is separated from Astenus DEJEAN 1833 (type species: Staphylinus angustatus PAYKULL 1789 = S. gracilis PAYKULL 1789 ) by the narrower abdomen, with tergites III-VI (without paratergites) at most twice as wide as long. This subgeneric concept has remained unquestioned ever since.

A study of various species previously attributed to Astenus and Astenognathus , however, yielded the following results:

a) The width of the anterior abdominal tergites is by no means a constant character among the species of either subgenus. Extreme character states are linked by fluent transitional conditions, suggesting that the width of the abdomen is an inadequate character for the separation of subgenera in Astenus .

b) This distinguishing character is neither clear-cut nor discreet. For instance, in A. pulchellus (HEER) - originally included in, and currently still attributed to Astenognathus - the anterior abdominal tergites are of exactly the same width as in A. immaculatus STEPHENS , which has been regarded as a representative of the subgenus Astenus by REITTER (1909) and subsequent authors.

c) Based on external characters such as the shape and chaetotaxy of the forebody, as well as on the morphology of the aedeagus, several species currently in Astenognathus , among them the type species A. bimaculatus , are close relatives of A. gracilis (type species) and other species in the subgenus Astenus . Also, these species are zoogeographically and ecologically similar in that they are widespread and not associated with ants, respectively.

d) There is some evidence that some species currently in Astenognathus (e. g. A. procerus , A. uniformis , and allied species) form a distinct lineage and may eventually have to be moved to a separate subgenus, possibly Eurysunius REITTER. However, this question can be decided only based on a thorough revision and will have to be considered in future studies.

In conclusion, there is no reasonable doubt that Astenognathus in the current sense is in fact a polyphyletic taxon. Based on the evidently close relationship of its type species, A. bimaculatus , to the type species of Astenus , A. gracilis , the following synonymy is proposed: Astenus DEJEAN 1833 = Astenognathus REITTER 1909 , nov.syn.