Hydrellia frontalis Loew, 1860

Hydrellia frontalis Loew, 1860 View in CoL

( Figs 25–33 View Figs 25–33 )

Hydrellia frontalis Loew, 1860: 19 View in CoL .

Type locality. Poland, Wrocław env. (see Remarks).

Type material examined. HOLOTYPF: ♀, directly pinned in good condition ( Figs 32, 33 View Figs 25–33 ), labelled: ʽ… 4. 6. 46 [handwritten, partly illegible, Fig. 32 View Figs 25–33 ] // Coll H. Loew [printed] // Hydrellia frontalis m. [handwritten] // Holotypus [red label, printed] // 14436 [printed] // Zool. Mus. Berlin [light yellow label, printed]ʼ ( ZMHB).

Additional specimens examined. CZECH REPUBLIC: BOHEMIA: Dolní Lhota, 49°22′31″N 13°14′41.5″E, alt. 400 m, Luňáky Nature Reserve, overgrown bottom of pond, yellow/white pan traps (2 days), 26.vii.2024, Z. Kejval leg.,2JJ 2♀♀ ( MCH, NMPC);same data, except: 31.vii.2024, 1 J 1 ♀ ( MCH). Tchořovice, 49°25′19″N 13°48′05″E, alt. 460 m, Smyslov Nature Monument, sweeping littoral vegetation of small pool, 23.viii.2024, Z. Kejval leg., 1 ♀ ( MCH).

Redescription. Male. Small shore flies; body length 2.6 mm, wing length 2.8–3.0 mm.

Head. Frons strongly transverse; parafrons brownish- -grey and with narrow bluish-grey strip along median margin of eyes, frontal vitta grey with slight bluish tinge ( Fig. 26 View Figs 25–33 ); ocellar, pseudopostocellar and fronto-orbital setae nearly equal, rather short, about 0.4 times as long as inner vertical seta. Antenna with scape and pedicel brownish black, basal flagellomere brownish black ( Figs 25, 26 View Figs 25–33 ); arista with 7–8 dorsal rays. Lunula brownish grey; face in anterior view silvery grey, in lateral view rather flattened; 7–8 facial setulae, minute to moderately long; palpus black, slightly broadened distally ( Figs 25, 26 View Figs 25–33 ); eye to gena ratio 8.2.

Thorax. Mesonotum subshiny, grey with slight bluish tinge anteriorly, more or less distinctly brownish posteriorly and especially on lateral sides, scutellum brownish, notopleura distinctly brown; pleurae largely grey, with bluish tinge, only dorsal half/third of anepisterum brown ( Fig. 25 View Figs 25–33 ). Presutural dorsocentral setae markedly shorter than first postsutural seta. Legs comparatively long, nearly entirely dark grey ( Fig. 25 View Figs 25–33 ), front coxa usually entirely pale reddish-brown, sometimes rather greyish laterally, as shown in photo 25, all trochanters, base and apex of tibiae with brownish tinge; covered by grey microtomentum, except for posterior side of hind leg; fore femur antero-ventrally on distal half with row of minute densely spaced spine-like setulae; distal half of mid femur with anterior row of moderately long setulae. Wing hyaline, with yellowish tinge, and with vaguely outlined dark apical spot, along apical part of vein R 4+5 ( Fig. 27 View Figs 25–33 ); veins largely brownish, paler at wing base, brownish black apically; costal vein ratio 0.78; M vein ratio 0.62; knob of halter white, stem pale reddish.

Abdomen. All terga largely grey with slight bluish tinge, except for narrow brownish strip along basal margin; external male terminalia pale brown; male fifth to fourth tergite ratio 0.8. Epandrium narrow without distinct setae, producing large cercal cavity; cercus conspicuously large, in dorsal view irregularly triangular ( Fig. 28 View Figs 25–33 ); genital plate in dorsal view moderately transverse, 0.7 times as long as wide, obcordate and its apical margin with deep triangular median emargination ( Fig. 28 View Figs 25–33 ), in lateral view narrowly triangular; aedeagus elongate, in dorsal view 2.29 times as long as wide, cylindrical with posterior margin slightly depressed, then tapered and narrow in anterior quarter, bearing latero-medial tooth-like shaped projections ( Fig. 29 View Figs 25–33 left), in lateral view 5.19 times as long as wide, irregularly stringbean-shaped with two-flaps on dorsal margin ( Fig. 29 View Figs 25–33 right); phallapodeme in dorsal view spatulate, with posterior part showing V-shaped dark chitinization, and anterior part bifurcated apically ( Fig. 30 View Figs 25–33 ), in lateral view L-shaped, of moderate width, with posterior margin forming zigzag ( Fig. 31 View Figs 25–33 ); postgonite in dorsal view forms arcuate spatula ( Fig. 30 View Figs 25–33 ), in lateral view elongate and narrow, with anterior process sinuate ( Fig. 31 View Figs 25–33 ); pregonite short, strongly narrowed apically, bearing one apical and one subapical setula ( Figs 30, 31 View Figs 25–33 ); hypandrium in dorsal view bullet-shaped with rounded anterior margin ( Fig. 30 View Figs 25–33 ), in lateral view moderately depressed ( Fig. 31 View Figs 25–33 ); 5 th sternum U-shaped and largely covered by setulae, pointing evenly posteriad; setulae markedly more robust and longer posteriorly ( Fig. 30 View Figs 25–33 ).

Female. Identical with male for most external characters; body length 2.9–3.0 mm; wing length 3.0– 3.1 mm; arista with 6–8 dorsal rays; 9–13 facial setulae ( Figs 32, 33 View Figs 25–33 ); eye to gena ratio 7.8–9.2; darker apical spot of wings indistinct or at most very slightly indicated; costal vein ratio 0.59; M vein ratio 0.76; cercus yellowish to pale reddish.

Biology. The specimens from the Luňáky Nature Reserve come from strongly overgrown muddy bottom of largely drained pond ( Fig. 37 View Figs 34–37 ). They were all collected by using water pan traps (yellow and white, diameter ca. 20 cm) placed at the edges of vegetation with dominant Glyceria maxima and Juncus effusus .

Distribution. Czech Republic (KARNFCKÁ 1985, here confirmed), Poland (LOFW 1860).

Remarks. LOFW (1860) described Hydrellia frontalis from a single specimen collected in the vicinity of Wrocław (ʽNähe von Breslauʼ) in Poland. It was later recorded from the Czech Republic ( Bohemia: Nítovice, Skopaný pond, ca. 49°10′10.6″N 14°47′37″E, 1J) (KARNFCKÁ 1985), but this record, as well as other suspect findings by H. Karnecká, was questioned by KUBÁTOVÁ- HIRšOVÁ (2003), and the species was later removed from the Czech checklist (cf. KUBÁTOVÁ- HIRšOVÁ 2009). The collection of H. Karnecká was never studied by other specialists and is in very poor condition in NMPC (M. Tkoč, pers. comm.).

The holotype is in good condition and the newly collected specimens (females) match it well, especially in having dark palpi, pale fore coxa, darkened brownish dorsal part of anepisternum and brownish base of abdominal terga. The darkened apex of wing in males of H. frontalis ( Fig. 27 View Figs 25–33 ) appears to be a unique case of sexual dimorphism within the genus.