Hydrellia pilsna, Zatwarnicki & Kejval, 2024

Hydrellia pilsna sp. nov.

( Figs 8–14 View Figs 8–14 )

Type locality. Czech Republic, Plzeň- Bolevec,banks of Velký Bolevecký rybník (pond), 49°46′33.5″N 13°23′27″E, altitude 310 m ( Fig. 35 View Figs 34–37 ).

Type material. HOLOTYPF: J, ʽCZ-Bocc 6246, 2.6.2022, PLZEŇ- Bolevec, Velký bolevecký rybník (pond banks), 310 m, Z. Kejval leg., 49°46′29″N 13°23′28″E [printed] // HOLOTYPE [red label, printed] // Hydrellia pilsna sp.nov. T. Zatwarnicki & Z. Kejval det. 2024 [printed]ʼ ( NMPC). PARATYPFs: 4 ♀♀, same locality data as holotype ( NMPC); 1 ♀, same data, except: 49°46′34.6″N 13°23′49″E, 6.6.2022 ( NMPC); 18 JJ 23 ♀♀, same data, except: 49°46′29″N 13°23′28″E, 18.7.2023 (25 ex. in NMPC, 4 ex. in each CULSP, MCH, SMOC, ZCM). GoogleMaps

Description. Male. Small shore flies; body length 1.6–1.9 mm, wing length 2.0– 2.4 mm.

Head. Frons longer than wide; parafrons dark, dull black with grey margin along eye margin, frontal vitta concolorous with parafrons ( Fig. 9 View Figs 8–14 ); length of pseudopostocellar seta is 1/2 of inner vertical seta length; ocellar seta stronger and 1.5 times longer than pseudopostocellar seta; fronto-orbital setae moderate, posterior one subequal to pseudopostocellar seta, anterior one 1/3 longer. Antenna with scape and pedicel black, basal flagellomere reddish with darker dorsal portion ( Figs 8, 9 View Figs 8–14 ); arista with 4 dorsal rays. Lunula grey; face in anterior view greyish brown, and more or less extensively paler/reddish medially, in lateral view gently and shallowly arched; 6 facial setulae; palpus reddish, spatulate ( Figs 8, 9 View Figs 8–14 ); eye to gena ratio 16.7.

Thorax. Mesonotum largely greyish-brown; postpronotum, notopleuron and supra-alar area, and side of scutellum grey; pleurae light grey ( Fig. 8 View Figs 8–14 ); presutural dorsocentral setae short. Legs distinctly bicolorous, coxae and majority of femora black, covered by grey microtomentum, trochanters, apices of femora, tibiae and tarsi reddish, apical tarsomeres sometimes moderately darkened ( Fig. 8 View Figs 8–14 ); fore femur bears postero-ventral row of small setulae; distal half of mid femur bears anterior row of moderate setulae. Wing hyaline with yellowish veins; costal vein ratio 0.58–0.76; M vein ratio 0.62–0.67; knob of halter white, stem yellow.

Abdomen. Terga dark brown, subshiny; male fifth to fourth tergite ratio 1.10. Epandrium in dorsal view narrowly U-shaped with moderately wide lateral arms, producing moderate cercal cavity ( Fig. 10 View Figs 8–14 ), arm in lateral view irregularly ovate, tapering posteriorly and rounded anteriorly, each bearing 5 strong setae; cercus small, in dorsal view irregularly triangular ( Fig. 10 View Figs 8–14 ); genital plate in dorsal view 1.05 times longer than wide, semi-oval, its anterior margin broadly rounded with deep medial indentation ( Fig. 10 View Figs 8–14 ), in lateral view ellipsoidal; aedeagus elongate, in dorsal view 3.50 times longer than wide, cylindrical with posterior margin slightly indented and tapered anteriorly to narrow clavate projection ( Fig. 11 View Figs 8–14 left), in lateral view 3.83 times as long as wide, lunate, broad basally, with its anterior section tapered apically to digital projection that is slightly corniform apically, with posterior margin distinctly concave, forming postero-ventral triangular fold ( Fig. 11 View Figs 8–14 right); phallapodeme in dorsal view narrow, Y-shaped, and bifurcated apically ( Fig. 12 View Figs 8–14 ), in lateral view sinuate with broad medial section and narrowed towards ends ( Fig. 13 View Figs 8–14 ); postgonite J-shaped with posterior section bearing semi-circular lobe, in lateral view semi-clavate with wavy ventral margin; anterior process of postgonite L-shaped ( Fig. 14 View Figs 8–14 ); pregonite slender, straight, digitiform, bearing 2 apical setulae ( Fig. 12 View Figs 8–14 ); hypandrium in dorsal view bullet-shaped with rounded anterior margin ( Figs 12, 14 View Figs 8–14 ), in lateral view longer than wide, shallowly depressed ( Fig. 13 View Figs 8–14 ); 5 th sternum U-shaped with numerous moderately long setulae, rather evenly pointing posteriad; setulae mostly sparsely scattered, denser, longer and more robust on/ along posterior margin ( Figs 12, 14 View Figs 8–14 ).

Female. Identical with male for most external characters; body length 1.9–2.4 mm; wing length 1.9–2.8 mm.

Differential diagnosis. Hydrellia pilsna sp. nov. may resemble H. concii Canzoneri & Meneghini, 1975 by conspicuously bicoloured legs, short fronto-orbital setae, 6 facial setulae, and general shape of aedeagus (especially in dorsal view). However, it can be distinguished from this species by arista with 4 dorsal rays, slender mid tibia in males (modified/swollen ʽallargateʼ for H. concii ), much less conspicuous median notch on anterior margin of genital plate, and lack of median subapical projection of aedeagus.

Etymology. The species epithet, pilsna , comes from the city of Plzeň (Pilzna, Pylzna or Plzna in some Latin documents from the 14 th century) and the Pilsner beer (also pilsener or simply pils), which is a sort of beer that took its name from the name of the city. In the past, Velký Bolevecký pond (type locality) was used as a source of ice for cooling beer by the famous Pilsner Urquell brewery, where the world’s first pale lager was produced in Plzeň in 1842. The epithet is a noun in apposition.

Biology. All specimens were collected exclusively by sweeping littoral vegetation ( Fig. 35 View Figs 34–37 ). The largest sample (18.vii.2023) was taken at a site with the following major plant genera/species: Alisma plantago-aquatica (a few/ single), Bolboschoenus sp. , Glyceria fluitans , Eleocharis palustris , Nuphar lutea , Phragmites australis , and Schoenoplectus lacustris (a few) and Typha sp.

The pond originally had a low water level and more diverse vegetation in the succession stage, which substantially changed after artificial filling. Since autumn 2022 the water level has gradually risen by about one meter and in 2024 the species was no longer found at the site.

Distribution. Czech Republic.