A new species of Gaurax from the Czech Republic (Diptera, Chloropidae)

Abstract Gauraxsiostrzonekisp. n. (Diptera, Chloropidae) is described from the Czech Republic and the main differential characters are illustrated. A key to the European species of the genus is provided.


Introduction
The genus Gaurax was erected by Loew (1863) for an American species G. festivus Loew. Species of the genus Gaurax are small black or yellow flies with black markings and with or without ommatrichia, shiny or slightly dusted ocellar triangle, and a rounded scutellum. The gena are usually covered with a silvery dust. The first flagellomere is oval or reniform. The arista are usually densely pubescent, but not thickened. The costal cell of the wing is unusually broad. Legs of males are without a femoral comb. Species of the genus Gaurax are variable in body colouration and size, and genitalia examination is usually necessary for species identification.
The larvae of several species are associated with bracket fungi, other fungi, decaying wood infested by insects and decaying vegetable matter, as well as in bird's nests (Komonen et al. 2004, Nartshuk and Andersson 2013, Nartshuk and Kurina 2014 and several authors before them observed the same. Other species have been reared from cones of Larix decidua, Picea abies, and from a twig of Pinus silvestris (Karps 1981;Nordlander and Grijpma 1991).

Materials and methods
The studied material was collected in 2010 and 2014 by the authors in Vráž (near Písek), and it is deposited in the collections of the Czech University of Life Sciences, Prague. The specimens were collected by pyramidal traps as illustrated in Fig. 1 (described by Barták and Roháček 2011) and by sawdust traps baited with oak sawdust (Fig. 2). Most of the specimens were originally preserved in alcohol and were dried and mounted using the method described by Barták (1997). The genitalia of the described species were macerated in 10 % KOH (24 hours, room temperature) and later stored together with the specimens on plastic tags and fixed with butyl-methacrylate copolymer of methyl-methacrylate, xylene. The genitalia and individual species were photographed using a Nikon D300 digital camera mounted on a Nikon SMZ-U microscope and images were edited with the computer software NIS-Elements 3.0. On average, each final image is from a stack of 15 layers. Images were improved using the software Adobe Photoshop. The genitalia served as models for the outline of the hand drawn illustrations; details were added by direct observation of the genitalia. The morphological terms used here and distribution follow Nartshuk and Andersson (2013). The length of the ocellar triangle was measured from the posterior margin of the posterior  ocelli to the apex of the main part of the ocellar triangle. The depth of the head was expressed as the distance between the uppermost part of the head and the lowest part of the gena (in lateral view). The head length was measured from the level of the posterior of the head horizontally to the level of the foremost extension of the anterior margin of frons or eye, excluding the antenna. All measurements (including body length) were taken from dry specimens (therefore the actual length may differ). The body lengths of males were measured from the antennal base to the hind end of the epandrium.

Genus Gaurax Loew, 1863
Gaurax Loew, 1863, Berl. ent. Ztschr., 7: 35. Diagnosis. Species with head 1.25× as deep as long, first flagellomere 1.3× as deep as long, body yellow with three black partly fused stripes, central stripe reaching scutellum and scutellum often dark. Gaurax siostrzoneki sp. n. is similar to G. flavoscutellatus. The main characters distinguishing these two species are as follows: Gaurax siostrzoneki has surstylus with two long curved extensions, one long, strong seta growing from the lower projection, and cercus short and enlarged at apical part. In G. flavoscutellatus surstylus is without spurs and cercus is short and narrowed.
Description. Male (Figs 3, 4). Body length 1.3-1.5 mm. Ground colour yellow. Head 1.25× as deep as long (lateral view), yellow with black occiput. Ocellar triangle occupying two-thirds of frons, yellow, shiny, and black on ocellar tubercle only, with one row of dark interfrontal setulae along sides. All setae and setulae on head black. First flagellomere 1.3× as deep as long, yellow, often darkened on outer margin (variable). Arista black. Eyes with ommatrichia. Depth of gena in front equal to the length of first flagellomere, gena with one row of dark setulae. Palpus yellow.    Thorax. Scutum shiny yellow with three black partly fused stripes, central stripe reaching scutellum, sometimes scutum completely dark. Scutellum yellow or dark, apical scutellar setae longer than lateral setae. Anepisternum, katepisternum, katepimeron, and meron shiny yellow with 1-4 small dark spots. Notopleural setae 1+1. Setae of thorax black. Wings not coloured. Haltere yellow. Legs completely yellow.
Abdomen: black dorsally and yellow ventrally. Male genitalia (Figs 5, 6): epandrium yellow with dark, wide, medial stripe, surstylus with two long curved extensions, one long, strong seta growing from the lower projection, cercus short and enlarged at apical part.

Acknowledgement
This paper was supported by S grant (specific research) of MSMT (Ministry of Education, Sports and Youth).