Pseudexechia tuomikoskii, Kjaerandsen, Jostein, 2009

Kjaerandsen, Jostein, 2009, The genus Pseudexechia Tuomikoski re-characterized, with a review of European species (Diptera: Mycetophilidae), Zootaxa 2056, pp. 1-45 : 18-22

Pseudexechia tuomikoskii sp. n.

( Figs 8 A–D)

Mycetophila trivittata var. b Staeger, 1840:261

Pseudexechia trisignata ; Chandler 1978:44, figs 3 & 5

Diagnostic characters. Rather similar to P. trisignata and P. pectinacea , but can be distinguished by its moderately bi-coloured pattern in dark greyish brown and yellow with a narrow pale band along margin of mesonotum. Distinctive features of the male terminalia include having rectangular hypandrial lobe with sharp apices and relative sharp corners; the ventral branch of gonostylus forming large, slightly asymmetrical spatula that is broadest apically; and the smooth whitish tip of dorsal branch of gonostylus being slightly clubshaped. Females are distinguished by the combination of coloration; having tergite VII straight dorsally, forming a straight, weakly crenulated posterior margin with short, stout seta; and by having truncated tip of sternite VIII. Also similar to P. inthanonensis Kjaerandsen, 1994 , described from Thailand, which has inverted thoracic colours (yellow stripes on brown ground), a distinctly more dilated apex of the dorsal branch of gonostylus and a more stretched hypandrial lobe ( Kjaerandsen 1994).

Etymology. Named in honour of Risto Tuomikoski (1911–1989) who in the early 1960s collected and identified this species as separate from P. trisignata . The collections after him at the museum of zoology in Helsinki, Finland, show that Tuomikoski took special interest in the genus Pseudexechia and identified and labelled a number of undescribed species at that time, both from Europe and from the Oriental region (J. Kjaerandsen in prep.).

Description. Male (n = 5, except where otherwise stated). Total length 5.2–6.5, 5.9 (n=8) mm. Wing length 3.54–4.46, 4.01 mm, or 2.95–3.57, 3.27 x as long as profemur. Antenna 1.7–2.04, 1.91 mm long.

Coloration (specimen in alcohol). Moderately bi-coloured in dark greyish brown and yellow; mesonotal stripes indistinct, diffusely defined and dark; pale humeral area extended to forming narrow pale band along entire margin of mesonotum. Wings unmarked, greyish tinted. Legs pale with indistinct dark spots on coxae and femur. Abdomen dark with small triangular, apical band on tergite II–V, tergite VI extra dark; terminalia dark yellow.

Head. Width / length to frontal tubercle 1.37–1.53, 1.46. First flagellomere 1.49–1.63, 1.56 times as long as second flagellomere. Second flagellomere 2–2.35, 2.11 times as long as wide. Median ocellus small but distinct, lateral ocellus touching compound eye. Length / width of clypeus 1.21–1.4, 1.29. Antepenultimate segment 0.14–0.17, 0.15 mm long, palpomere ratios 1: 1.25–1.4, 1.32: 2.08–2.58, 2.33.

Thorax. Mesonotum length 1.04–1.26, 1.17 mm, or 0.28–0.32, 0.29 x as long as wing. Proepisternum with 1 strong bristle.

Wings. Wing length to length of R1 2.22–2.3, 2.25; wing length to length of R5 1.7–1.81, 1.73. Length of r-m to length of M-petiole 1–1.33, 1.15. R4+5-bending index 1.46–1.84, 1.61. Fork length ratio 0.88–0.95, 0.91. Fork width ratio 0.87–1.04, 0.92. M-ratios 0.58–0.74, 0.66 and 0.66–0.82, 0.74. CuA-ratios 1.11–1.28, 1.21 and 1.57–1.83, 1.69. CuP length to length of wing 0.44–0.57, 0.48. A1 length to length of wing 0.32–0.36, 0.33.

Legs. Leg ratios given for fore, mid and hind leg: LR 1.06–1.14, 1.1: 0.8–0.9, 0.85: 0.64–0.74, 0.71; SV 1.62–1.86, 1.7: 1.96–2.18, 2.05: 2.37–2.68, 2.44; BV 1.6–1.72, 1.66: 2.16–2.32, 2.22: 3.3–3.67, 3.48; TR 1.47–1.52, 1.51: 1.76–1.84, 1.79: 2.15–2.39, 2.3.

Terminalia ( Figs 8 A–C). Gonocoxite subrectangular, with distinct condyles; sternal sclerite forming small, sclerotized, bifurcated plate. Hypandrial lobe subrectangular, with sharp apices and blunt corners. Aedeagal guides subrectangular, but apically rounded. Gonostylus large; dorsal branch elongated, with slightly club-shaped, whitish tip; dorsointernal branch forming large, asymmetric, broad lamellate fan; medial branch present as large knob with three setae; ventral branch forming large, slightly asymmetrical spatula, widest at apex, ventrolaterad with 2–4 fan-tipped setae; internal branch forming large, striated cushion; anterior branch forming ventrally directed, subrectangular cushion. Tergite IX wide subrectangular, fused, with strong mesal suture. Pseudocercus long, setose. Cercus forming small knob, 1.75–2.4, 1.98 as long as wide in dorsal view. Hypoproct triangular, apiculate. Epiproct vestigial or absent.

Female (n = 1). Total length 6 mm. Wing length 4.28 mm, or 3.34 x as long as profemur. Antenna 1.7 mm long.

Coloration. As in male except tergite VI and VII also with pale apical bands.

Head. Width / length to frontal tubercle 1.41. First flagellomere 1.49 times as long as second flagellomere. Second flagellomere 2.53 times as long as wide. Median ocellus small but distinct, lateral ocellus touching compound eye. Length / width of clypeus 1.4. Antepenultimate segment 0.17 mm long, palpomere ratios 1: 1.3: 1.95.

Thorax. Mesonotum length 1.28 mm, or 0.3 x as long as wing. Proepisternum with 1 strong bristle.

Wings. Wing length to length of R1 2.23; wing length to length of R5 1.77. Length of r-m to length of Mpetiole 1.25. R4+5-bending index 1.33. Fork length ratio 0.9. Fork width ratios 0.96. M-ratios 0.64 and 0.73. CuA-ratios 1.2 and 1.69. CuP length to length of wing 0.46. A1 length to length of wing 0.33.

Legs. Leg ratios given for fore, mid and hind leg: LR 1.11: 0.88: 0.72; SV 1.68: 2.04: 2.41; BV 1.83: 2.31: 3.9; TR 1.61: 1.86: 2.84.

Terminalia. Tergite VII straight dorsally, with smooth posterior edge; apicolateral corner with nude area; setae along margin short, stout. Tergite VIII wide, subrectangular. Tergite IX fused with postgenital plate. Cercus one-segmented, long sinusoid with obtuse tip, as long as wide in lateral view. Postgenital plate (gonapophysis IX) elongated, with obtuse tip. Sternite VII subequal in length to tergite VII. Sternite VIII apically truncated. Gonapophysis VIII weak, narrow.

Remarks. The single female associated to the new species is confusingly similar to P. trisignata and to P. pectinacea . The association is based on the slightly diverged terminalia in combination with a good coloration match with the male. The diagnostic characters further seem to fit well with the female that was illustrated by Chandler (1978, fig. 5), who also figured the male of this species under the name P. trisignata .

Distribution. The confirmed records from Norway, Sweden, Great Britain ( Chandler 1978) and probably France indicate a western European distribution.

Biology unknown.

Holotype male: NORWAY: MRI, Sunndal, Jordalsgrenda, Jordalsøra, Hamrene, 62°46'18"N, 008°19'12"E, 140 m a.s.l. 23 Oct–11 Nov 2005 (Leg. J. B. Jordal) [ MZLU, JKJ – SPM – 013145, on slide].

Paratypes: NORWAY: MRI, Sunndal, Jordalsgrenda, Jordalsøra, Hamrene, 62°46'18"N, 008°19'12"E, 140 m a.s.l. 6–23 Oct 2005 (Leg. J. B. Jordal) — 1 male [ MZLU, JKJ – SPM – 011950, on slide]; 23 Oct–11 Nov 2005 (Leg. J. B. Jordal) — 1 male [ MZLU, JKJ – SPM – 011950, on slide]; FV, Alta, Mattisdalen (S), SEfaced slope, 69°50'6''N, 22°51'23''E, 4 Aug–26 Sep 1996 (Leg. L.O. Hansen & H. Rinden) — 1 female [ ZMUN, JKJ – SPM –005565, on slide]; Alta, Elvestrand, 69°57'12''N, 23°15'32''E, 18 Jul–16 Sep 1996 (Leg. H. Rinden) — 1 male [ MZLU, JKJ – SPM – 011880 on slide]; SWEDEN: SK, Blentarp, Stampenbäcken, 55°35'53''N, 13°33'12''E, 25 Sep 1969 (Leg. B. W. Svensson) — 1 male [ MZLU, JKJ – SPM –004651, on slide].

Additional material examined: NORWAY: FØ, Tana, Nedre Storfosen, 70°4'47''N, 27°40'25''E, 4 Jul 1964 ( MZH, Leg. R. Tuomikoski) — 1 male; FV, Alta, Elvestrand, 69°57'12''N, 23°15'32''E, 18 Jul–16 Sep 1996 ( ZMUN, Leg. H. Rinden) — 1 male; Kvalsund, Skaidi, 70°25'56''N, 24°29'24''E 7, Jul 1964 ( MZH, Leg. R. Tuomikoski) — 1 male; MRI, Sunndal, Jordalsgrenda, Jordalsøra, Hamrene, 62°46'18"N, 008°19'12"E, 140 m a.s.l., 15 Sep–6 Oct 2005 ( MZLU, Leg. J. B. Jordal) — 2 males; 6–23 Oct 2005 ( MZLU, Leg. J. B. Jordal) — 1 male; TRY, Kvaenangsfjord, 69°45'51''N, 21°56'45''E, 8 Jul 1964 ( MZH, Leg. R. Tuomikoski) — 1 male. SWEDEN: SK, Blentarp, Stampenbäcken, 55°35'53''N, 13°33'12''E, 10 Nov 1969 ( MZLU, Leg. B. W. Svensson) — 1 male; 20 Nov 1969 ( MZLU, Leg. B. W. Svensson) — 1 male. DENMARK: Frederiksberg, undated ( ZMUC, Leg. C. Staeger) — 2 males (paralectotypes of M. trivittata , var. b).? FRANCE: Without label (sans étiquette), from general collection MNHN, terminalia mounted on slide by L. Matile — 1 male.

Figures

FIGURE 8. Pseudexechia tuomikoskii sp. n. — A. Male terminalia, ventral view. — B. Male gonostylus, internal view. — C. Male tergite IX and cerci, dorsal view. — D. Female terminalia, lateral view.