Pseudexechia tristriata Stackelberg 1969

Pseudexechia tristriata (Stackelberg, 1969)

(Figs 14 A–D)

Exechia tristriata Stackelberg in Ostroverkhova & Stackelberg, 1969:299 [in English translation page 453, figs 185, 3a & 3b]

Pseudexechia tristriata; Ostroverkhova, 1979:168, fig. 32,3

Pseudexechia tristriata; Krivosheina et al. 1986:155, figs 45,3 & 45,4

Pseudexechia tristriata; Zaitzev 1999:188, figs 109,2 & 109,3

Pseudexechia tristriata; Zaitzev 2003:193, figs 43,2 & 43,6

Diagnostic characters. A distinctly bi-coloured species in dark greyish brown and yellow, often with a reddish tinge, with distinct, sharply defined thoracic stripes. Distinctive features of the male terminalia include having the ventral branch of the gonostylus larger than the dorsal branch, the former being covered with seta on the medial surface while the latter is almost devoid of medial setae. Females have almost identical terminalia with P. trivittata, but can be distinguished by the vivid coloration.

Description. Male (n = 3, except where otherwise stated). Total length 4.5–5.2 (n=4) mm. Wing length 3.36–3.48 mm, or 3.23–3.29 x as long as profemur. Antenna 1.4–1.46 mm long.

Coloration (specimen in alcohol). Distinctly bi-coloured in dark greyish brown and yellow, often with a reddish tinge; mesonotal stripes distinct, sharply defined, dark; humeral area narrowly pale. Wings unmarked, yellowish tinted. Legs pale, sometimes with indistinct dark spots on femur. Abdomen dark with triangular, gradually smaller, apical bands on tergite II–VI; terminalia dark yellow.

Head. Width / length to frontal tubercle 1.4–1.44. First flagellomere 1.87–2.07 times as long as second flagellomere. Second flagellomere 1.35–1.75 times as long as wide. Median ocellus vestigial or absent, lateral ocellus touching compound eye. Length / width of clypeus 0.83–1.08. Antepenultimate segment 0.11–0.12 mm long, palpomere ratios 1: 1.18–1.34: 2.63–3.06.

Thorax. Mesonotum length 1–1.06 mm, or 0.29–0.32 x as long as wing. Proepisternum with 2 strong bristles.

Wings. Wing length to length of R1 2.24–2.4; wing length to length of R5 1.76–1.83. Length of r-m to length of M-petiole 1–1.25. R4+5-bending index 0.96–1.09. Fork length ratio 0.8–0.83. Fork width ratio 1–1.25. M-ratios 0.59–0.66 and 0.67–0.77. CuA-ratios 1.45–1.69 and 1.79–2.37. CuP length to length of wing 0.45–0.48. A1 length to length of wing 0.31–0.36.

Legs. Leg ratios given for fore, mid and hind leg: LR 1.09–1.11: 0.81–0.82: 0.64–0.68; SV 1.65–1.66: 2.11–2.13: 2.54–2.66; BV 1.62–1.69: 2.07–2.12: 3.1–3.17; TR 1.51–1.59: 1.63–1.7: 1.91–1.97.

Terminalia (Figs 14 A–C). Gonocoxite subrectangular, with indistinct condyles; sternal sclerite forming longitudinal suture. Hypandrial lobe long, parallel sided, with blunt apices and small split. Aedeagal guides elongated, lying dorsad of internal branch of gonostylus. Gonostylus large, elongated; dorsal branch elongated, lanceolate, without whitish tip; dorsointernal branch reduced to hyaline knob basally on dorsal branch; medial branch reduced or fused with internal branch; ventral branch forming large, angular, lanceolate lobe, densely covered with short setae on both sides; internal branch forming small, striated cushion; anterior branch forming hyaline, irregular plate with many small, blunt projections caudally. Tergite IX long subrectangular, fused, with weak mesal suture. Pseudocercus medium sized, setose. Cercus forming small knob, 1.33–1.62 (n=2) as long as wide in dorsal view. Hypoproct triangular, apiculate. Epiproct vestigial or absent.

Female (n = 1). Total length 5.1 mm. Wing length 3.18 mm, or 3.18 x as long as profemur. Antenna 1.38 mm long.

Coloration. As in male except larger triangular pale apical bands on tergite II–VII.

Head. Width / length to frontal tubercle 1.5. First flagellomere 1.77 times as long as second flagellomere. Second flagellomere 1.76 times as long as wide. Median ocellus vestigial or absent, lateral ocellus touching compound eye. Length / width of clypeus 1.18. Antepenultimate segment 0.11 mm long, palpomere ratios 1: 1.49: 3.09.

Thorax. Mesonotum length 1.06 mm, or 0.33 x as long as wing. Proepisternum with 2 strong bristles.

Wings. Wing length to length of R1 2.27; wing length to length of R5 1.71. Length of r-m to length of Mpetiole 1.33. R4+5-bending index 1.19. Fork length ratio 0.79. Fork width ratio 1. M-ratios 0.56 and 0.63. CuAratios 1.31 and 1.8. CuP length to length of wing 0.42. A1 length to length of wing 0.32.

Legs. Leg ratios given for fore, mid and hind leg: LR 1.11: 0.83: 0.66; SV 1.62: 2.12: 2.6; BV 1.72: 2.1: 3.08; TR 1.6: 1.65: 1.91.

Terminalia (Fig. 14 D). Tergite VII excavated dorsally, with slightly dentate to laciniate, acute posterior edge; apicolateral corner without nude area; setae along margin long, slender. Tergite VIII wide, subrectangular. Tergite IX fused with postgenital plate. Cercus one-segmented, short sinusoid with acute tip, 2.5 as long as wide in lateral view. Postgenital plate (gonapophysis IX) short, broad, with acute tip. Sternite VII subequal in length to tergite VII. Sternite VIII acute. Gonapophysis VIII strong, broad.

Distribution. Palaearctic, mainly easterly in Europe.

Biology. Adults have been reared form Thelephora terrestris (Yakovlev 1994).

Material examined. FINLAND: N, Esbo, Bodom, 60°15'58''N, 24°41'25''E, 9 Oct 1962 (MZH, Leg. W. Hackman) — 1 male; Helsinki, Nordsjö, [60°12'26''N, 25°8' 5''E] 22 Apr 1962 (MZH, Leg. R. Tuomikoski) — 1 male; Vihti, Vihtijärvi, 60°31'32''N, 24°32'22''E, 26 Apr 1964 (MZH, Leg. R. Tuomikoski) — 1 male; Ta, Lammi, Trailing area Evo [61°11'34''N, 25°6'29''E], Old-growth spruce-dominated forest, Evo, trap no. 1, 18 Aug–2 Sep 2003 (MZH, Leg. J. Jakovlev) — 1 male; Trailing area Evo, Burnt clear-cut area with retention trees, Evo, trap no. 7, 15 Sep–3 Oct 2003 (MZLU, Leg. J. Jakovlev) — 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., 13 Aug–13 Oct 2004 (MZLU, Leg. M. Karström) — 1 female.