On the taxonomy and natural history of Oxypoda brachyptera and O . tarda ( Coleoptera : Staphylinidae : Aleocharinae )

Based on a revision of types and additional material, Oxypoda brachyptera (Stephens, 1832) and O. tarda Sharp, 1871, two species with a controversial and confusing taxonomic history, are regarded as distinct species, redescribed, and illustrated. A lectotype is designated for Oxypoda tarda. Numerous field studies conducted in northwestern Germany during the period from 1981 through 2001 yielded approximately 8,500 adult specimens of O. brachyptera and O. tarda. Based on these data, as well as on anatomical studies, the life histories of both species, including their seasonal activity, seasonal density, reproduction periods, duration of pre-imaginal development, and pupal emergence, are investigated. Both species are epigeically active from spring through autumn, develop without diapause, and hibernate in the adult stage. In contrast to Oxypoda tarda, which has only one generation per year, O. brachyptera is apparently bivoltine. Both species are generally found in open, unshaded biotopes. Nevertheless, regarding their respective habitats, they are distinctly segregated. While O. brachyptera was recorded from drier and wamer habitats on sandy or calcareous soils, O. tarda usually occurs in moist localities on heavier soils. Rarely, they were found to occur syntopically. Both species are wing-dimorphic, the macropterous morph being distinctly rarer than the micropterous morph; the dimorphism is not sex-related.

The abdomen o f several thousand females was dissected to examine the condition o f the ovaries.
The presence o f mature eggs was interpreted as evidence o f oviposition activity. In all the studied specimens the length o f the hind wings was recorded. In order to assess the presence or absence o f flight muscles, the thorax o f more than a hundred macropterous specimens was dissected by removing the dorsal portion o f the thoracal ectoscleleton.

Ecology:
During a period o f more than two decades (1 9 8 1-2 0 0 1), field studies were conducted on the staphylinid fauna o f a variety o f habitats, particularly Calluna heathlands on sandy soils, in Niedersachsen, northern Germany. These studies yielded more than 10 0 ,0 0 0 adult Staphylinidae and more than 15 ,0 0 0 larvae. The localities where either Oxypoda brachyptera or O. tarda were recorded are listed in Tab. 1. For more details on these sites see AssiNG (1988,1992,1993,1994 In all the study sites pitfall traps were used to assess the species inventory and seasonal activity. The number o f pitfall traps varied between three and 52 per year and site. For details regarding the type, construction, and maintenance o f the pitfall traps see M elber (198 7 ). The traps remained installed throughout the year (i.e., also in winter) and were emptied at half-monthly intervals, in some sites at m onthly intervals. The data shown in Figs 2 6 -2 7 are exclusively based on those full-year studies with pitfall traps that were emptied at half-m onthly intervals. In all, more than 7 0 0 one-year pitfall traps were installed and maintained.
In addition to pitfall trapping, soil extractions after Kempson et al. (1963) were conducted in several heathlands to assess the densities o f Staphylinidae. The samples were taken at half m onthly intervals throughout the year. For more inform ation on the field methods used see AssiNG (1993

Comment:
The original description o f Aleochara brachyptera is based on an unspecified number o f syntypes from "Norfolk" and "Barham" (Stephens 1832

Redescription:
Small species; body length 2.2-2.6 mm. Coloration variable; usual coloration: head reddishbrown to blackish-brown; pronotum and elytra reddish-yellow to reddish; abdomen reddish, with segment V I and anterior portion o f segment VII infuscate; legs yellowish to reddish-yellow; antennae dark-yellowish to brown. Occasionally, especially in macropterous specimens, the color ation is significantly darker, with the head almost blackish, the pronotum and elytra dark-brown, and the abdomen more extensively infuscate.
Head transverse; eyes moderately large, approximately as long as postocular portion in lateral view, not larger in macropterous than in micropterous specimens. Antenna relatively long and massive, moderately and gradually incrassate apically; preapical antennomeres approximately 1.5 times as wide as long; antennomere XI with weakly pronounced sexual dimorphism, on average slightly longer in males than in females. Maxillary palpus not conspicuously elongated; preapical palpomere approximately 3 times as long as wide.
Pronotum approximately 1.35 times as broad as long, widest approximately in the middle; hind margin broadly convex, not distinctly bisinuate; punctation dense and shallow; interstices with microsculpture ( Fig. 1).

Additional material examined:
Apart from the material listed in Tab. 2, the following material was studied: Germany Elytra dimorphic, in micropterous morph 0.7 5-0 .9 0 times, in macropterous morph 0 .9 0 0.95 times as long as pronotum. Hind wings either fully developed (macropterous morph) or reduced to short stubs (micropterous morph), these rudiments slightly longer than elytra.
Abdomen punctation o f tergite VII practically as dense as that o f anterior tergites (Fig. 10)  Habitat. In northern Germany, O. tarda is not particularly rare. The examined material was found in various unforested, generally in more or less moist habitats on heavier, often more or less loamy, or on calcareous soils, particularly in moist meadows, floodplains, arable land, fallows, and in coastal meadows. The species appears to be absent from dry habitats on sandy soils.
According to Lohse (