Pseudexechia canalicula ( Johannsen, 1912 )

Kjaerandsen, Jostein, 2009, The genus Pseudexechia Tuomikoski re-characterized, with a review of European species (Diptera: Mycetophilidae), Zootaxa 2056, pp. 1-45 : 23-24

Pseudexechia canalicula ( Johannsen, 1912)

( Figs 2 C, 5C, 9A–D)

Exechia canalicula Johannsen, 1912:69 , fig. 36

Exechia canalicula ; Shaw & Fisher 1952:202, fig. 33

Diagnostic characters. With its large gonostylus the male show some resemblance to the species of the trisignata group, but has the mesonotal stripes distinctly separated, a conically tapered hypandrial lobe and subsymmetric dorsointernal branch of the gonostylus. Further distinctive features of the male terminalia include a distinctly club-shaped dorsal branch of the gonostylus, and the ventral branch forming a large, subrectangular spatula. Females are characterized by the combination of a two-segmented cercus and tergite VII with smooth, straight posterior edge that is prolonged dorsally.

Description. Male (n = 4, except where otherwise stated). Total length 4.7–6, 5.4 (n=8) mm. Wing length 3.48–3.84 mm, or 3.22–3.36 x as long as profemur. Antenna 1.5–1.56 mm long.

Coloration (specimen in alcohol). Distinctly bi-coloured in dark greyish brown and yellow; mesonotal stripes distinct, but less sharply defined, dark; humeral area less pale. Wings unmarked, yellowish tinted. Legs all pale. Abdomen dark with small triangular, apical band on tergite II–IV, tergite V & VI all dark; terminalia dark yellow.

Head. Width / length to frontal tubercle 1.39–1.58. First flagellomere 1.88–2.07 times as long as second flagellomere. Second flagellomere 1.36–1.72 times as long as wide. Median ocellus vestigial or absent, lateral ocellus touching compound eye. Length / width of clypeus 1.22–1.35. Antepenultimate segment 0.13–0.15 mm long, palpomere ratios 1: 1.06–1.3: 1.93–2.16.

Thorax. Mesonotum length 1.08–1.2 mm, or 0.3–0.32 x as long as wing. Proepisternum with (1–) 2 strong bristles.

Wings. Wing length to length of R1 2.31–2.45; wing length to length of R5 1.78–1.83. Length of r-m to length of M-petiole 1.07–1.36. R4+5-bending index 1.04–1.26. Fork length ratio 0.8–0.85. Fork width ratio 0.88–1.17. M-ratios 0.58–0.64 and 0.67–0.73. CuA-ratios 1.35–1.56 and 1.87–2.12. CuP length to length of wing 0.44–0.47. A1 length to length of wing 0.3–0.36.

Legs. Leg ratios given for fore, mid and hind leg: LR 1.02–1.17: 0.81–0.85: 0.67–0.69 (n=3); SV 1.63–1.83: 2.05–2.16: 2.5–2.61 (n=3); BV 1.61–1.69: 2.09–2.29: 3.07–3.47 (n=2); TR 1.49–1.6: 1.66–1.77: 2–2.32 (n=3).

Terminalia ( Figs 9 A–C). Gonocoxite rounded, with less distinct condyles; sternal sclerite forming short, cordate plate. Hypandrial lobe triangular, conically tapered. Aedeagal guide forming elongated lobe. Gonostylus large; dorsal branch elongated, with distinctly club-shaped, whitish tip; dorsointernal branch forming large, subsymmetric, broad lamellate fan with long stalk; medial branch present as small knob with three setae; ventral branch forming large, subrectangular, slightly asymmetrical spatula, apically somewhat tapered and slightly serrated, ventrolaterad with 2–4 fan-tipped setae; internal branch forming large, striated cushion; anterior branch forming ventrally directed, subrectangular cushion. Tergite IX subquadrate, fused, with strong mesal suture. Pseudocercus moderately long, setose. Cercus forming small knob, 1.31–1.54 as long as wide in dorsal view. Hypoproct long, acuminate. Epiproct vestigial or absent.

Female (n = 3, except where otherwise stated). Total length 5–5.5 (n=4) mm. Wing length 3.74–3.78 mm, or 3.4–3.48 x as long as profemur. Antenna 1.34–1.4 mm long.

Coloration. As in male except tergite VII also all dark.

Head. Width / length to frontal tubercle 1.38–1.5. First flagellomere 1.88–2.46 times as long as second flagellomere. Second flagellomere 1.2–1.53 times as long as wide. Median ocellus vestigial or absent, lateral ocellus touching compound eye. Length / width of clypeus 1.11–1.18. Antepenultimate segment 0.14–0.15 mm long, palpomere ratios 1: 1.12–1.22: 2.24–2.36.

Thorax. Mesonotum length 1.14–1.16 mm, or 0.3–0.31 x as long as wing. Proepisternum with 2 strong bristles.

Wings. Wing length to length of R1 2.27–2.3; wing length to length of R5 1.7–1.8. Length of r-m to length of M-petiole 1.08–1.56. R4+5-bending index 0.88–1.25. Fork length ratio 0.74–0.85. Fork width ratio 0.96–1.19. M-ratios 0.54–0.62 and 0.63–0.7. CuA-ratios 1.29–1.54 and 1.83–2.1. CuP length to length of wing 0.44–0.48. A1 length to length of wing 0.3–0.35.

Legs. Leg ratios given for fore, mid and hind leg: LR 1.08–1.13: 0.82–0.84: 0.65–0.68; SV 1.65–1.74: 2.08–2.14: 2.51–2.65; BV 1.69–1.75: 2.17–2.29: 2.96–3.23; TR 1.59–1.7: 1.71–1.89: 1.92–2.03.

Terminalia ( Fig. 9 D). Tergite VII prolonged dorsally, with smooth straight posterior edge; apicolateral corner with nude area; setae along margin long, slender. Tergite VIII wide, subrectangular. Tergite IX fused with postgenital plate. Cercus two-segmented, apical segment ovate, the two combined 2.79–3.32 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 slightly truncated apically. Gonapophysis VIII more strongly developed, broad.

Distribution. Holarctic, in the Palaearctic region known only from the Nordic region ( Finland, Sweden and Norway).

Biology unknown.

Type material examined: Holotype male, USA: North Carolina, 35°10'14"N, 079°51'40"W, July, year unknown [ CUIC, JKJ – SPM –015088, Leg. O. A. Johannsen]. Holotype in poor condition, terminalia mounted on slide in the 70s—although very hyaline and difficult to interpret clearly conspecific with Nordic material.

Other material examined: FINLAND: N, Tvärminne, 59°50'31''N, 23°12'6''E, 14 Jun 1966 ( MZH, Leg. K. Keynäs) — 1 male; NORWAY: TRY, Kvaenangen, Kvaenangen, 69°43'33''N, 22°4'45''E, 25 Jul 1965 ( MZH, Leg. R. Tuomikoski) — 1 male; SWEDEN: LU, Jokkmokk, Porsitjärn/Porsi VVO, 1.5 km SE Vuollerim, 66°25'28''N, 20°40'17''E, 60 m a.s.l., 14 Apr–18 Oct 2003 ( MZLU, Leg. M. Karström) — 1 female; 6 May–13 Aug 2004 ( MZLU, Leg. M. Karström) — 4 males; 13 Aug–13 Oct 2004 ( MZLU, Leg. M. Karström) — 1 female, 1 male; 15 May–1 Jun 2005 ( MZLU, Leg. K. Hedmark & M. Karström) — 2 males; 16 Sep–1 Oct 2005 ( MZLU, Leg. K. Hedmark & M. Karström) — 4 males; 1–16 Oct 2005 ( MZLU, Leg. K. Hedmark & M. Karström) — 1 female; USA: Alaska, Palmer, 61°35'55"N, 149°07'21"W, 13 Jul 1964 ( USNM, Leg. K. M. Sommerman) — 2 females.

Figures

FIGURE 2. Habitus photos of Pseudexechia. — A. P. trisignata (Edwards, 1913) in lateral view, a dull brown species with a distinct greyish dusting, with fused thoracic stripes and narrow apical pale bands on abdomen. — B. P. aurivernica Chandler, 1978 in lateral view, a distinctly bi-coloured species in dark greyish brown and yellow, often with a reddish tinge, with distinct thoracic stripes and with large, triangular apical pale bands on abdomen — C. P. canalicula (Johannsen, 1912) in dorsal view, yet another bi-coloured species in greyish brown and yellow with distinct thoracic stripes.

FIGURE 9. Pseudexechia canalicula (Johannsen, 1912). — A. Male terminalia, ventral view. — B. Male gonostylus, internal view, enlarged. — C. Male tergite IX and cerci, dorsal view. — D. Female terminalia, lateral view.