Pseudexechia Tuomikoski

Kjaerandsen, Jostein, 2009, The genus Pseudexechia Tuomikoski re-characterized, with a review of European species (Diptera: Mycetophilidae), Zootaxa 2056, pp. 1-45 : 5-10

Genus Pseudexechia Tuomikoski

Pseudexechia Tuomikoski, 1966:180

Type species. Exechia trisignata Edwards, 1913 by subsequent designation.

Diagnosis. Species of the genus Pseudexechia are medium sized to small, slender exechiines, body length 3.5–6.5 mm ( Fig. 2 ). They can be recognized by the combination of the following characters: Ovate clypeus ( Figs 4 A&E). Vestigial, but usually traceable median ocellus (distinct but reduced in size in the trisignata group, Fig. 4 A). Absence of distinct bristles on the mesoscutal disc, except along the margin ( Fig. 4 F) and sometimes one pair posteriorly. Wings (Fig. 3) with vein sc more or less distinctly ending in R1, Cu branching beyond level of M branching (with one exception, see Kjaerandsen 1994), M-petiole subequal in length to cross vein ta (ratio 0.87–1.56, 1.16, n=65), branches of M and Cu without setulae. Male terminalia characteristic; usually with a strongly sclerotized, bud-like hypandrial lobe with a small median split (e.g. Fig. 6 A), ventral branch of gonostylus always with one long and one shorter, whip-like seta basally, often with a few characteristically fan-tipped setae ventrally ( Fig. 5 A), tergite IX without pair of extra long, apically truncated bristles ( Fig. 6 C), and pseudocercus slender and distinctly articulated ( Fig. 5 B, 6C). Female terminalia with sclerotized postgenital plate ( Fig. 5 C), usually with one-segmented (e.g. Fig. 6 D), but sometimes two-segmented ( Fig. 5 C) cercus.

Description. Adults: Medium sized to small, slender with long legs and long abdomen ( Fig. 2 ), body length 3.5–6.5 mm.

Head. Antenna ( Figs 4 B–C) with 14 flagellomeres; scape and pedicel with a few close set stout bristles ventromedially and dorsally, otherwise with scattered small setae apically; flagellars long rectangular, densely covered with medium sized pale, decumbent setae, some short stiff setae along ventral side; scape, pedicel and half of first flagellar pale, rest of flagellum darker. Vertex with five strong orbital bristles, otherwise covered with medium sized, decumbent dark setae. Ocelli ( Fig. 4 A) three or two, lateral ocellus touching eye margin, median ocellus either small but distinct or vestigial but usually traceable. Frontal furrow reduced, not reaching frontal tubercle. Face ( Fig. 4 E) wide rectangular, with scattered small setae. Clypeus ( Fig. 4 E) long ovate to subcircular, covered with small setae. Palp ( Figs 4 A&D) with four distinct palpomeres; sensory pit in third palpomere forming an ovate open furrow medially, with trichoid sensillae in internal sac; fifth palpomere as long as or longer than third and fourth palpomere combined.

Thorax ( Fig. 4 F). Proepisternum with 1–2 and antepronotum with 3 strong bristles. Scutum without distinct acrostichals and dorsocentrals, with strong prealar and postalar and sometimes with one pair of posteriorly situated bristles, otherwise covered with small to medium sized setae; with or without dark thoracic stripes on pale ground and pale band along lateral margin. Scutellum with one strong and one weaker pair of bristles otherwise covered with small setae. Anepisternum, anepimeron and preepisternum completely devoid of setae. Laterotergite scattered with tiny, thin setae and some large bristles. Mediotergite bare or at most with a couple of setae. Metepisternum posteriorly with a few bristles and some tiny setae. Metepimeron with some scattered tiny setae.

Wings (Fig. 3). Wing membrane unspotted yellowish tinted or with faintly smoked apical half and faint cloud around branching of media; with microtrichia only, trichia dark and arranged into regular rows apically. Basicosta with 1–2 strong bristles. Crossvein h without setae. Distal medial plate without setae both on dorsal and ventral side. Costa, R, R1and R5 with both dorsal and ventral setae. Sc, tb, ta, M, CuA, CuP, A1 and A2 without setae. Costa terminates at tip of R5. R4 absent. R5 straight to moderately curved posteriorly. Crossvein ta with small white spot. M-fork long, M-petiole subequal in length to crossvein ta (0.87–1.56, 1.16, n=65). CuA-fork shorter, starts (with one exception, see Kjaerandsen 1994) distinctly beyond M-fork. CuP long and basally strong, fading out about at level of CuA branching. A1 shorter, distinct and strong, breaking abruptly well before CuA-fork. A2 distinct, fading out about at level of A1.

Legs ( Figs 4 F&G–J). Setosity dark. Fore coxa covered with small setae on anterior and lateral surface, anteriorly and apically with strong bristles. Mid coxa with narrow row of small setae anteriorly; bare basolaterally, apical third with narrow row of small setae laterally; apically with larger setae and some bristles. Hind coxa with one strong bristle basolaterally; with narrow row of small setae along posterolateral surface; apically with larger setae and some bristles. Femora uniformly covered with small setae. Tibiae with trichia in regular rows. Fore tibia with short anteroventral and posterior bristles, anteroapically with round depressed FIGURE 3. Wing photos of Pseudexechia . —A. P. trisignata ( Edwards, 1913) . —B. P. aurivernica Chandler, 1978 . —C. P. trivittata ( Staeger, 1840) . —D. P. parallela ( Edwards, 1925) . Abbreviations: A = distance between base of the distal median plate to the branching of media; A1 = anterior anal vein; A2 = posterior anal vein; B = distance between base of the distal median plate to the branching of CuA; bc = basicosta; C = distance between R1 and R4+5 termination; CuA1 and CuA2 = anterior branch of cubitus; CuP = posterior branch of cubitus; D = distance between R5 and M1 termination; E = distance between M1 and M2 termination; F = distance between CuA1 and CuA2 termination; h = humeral; M-pet = petiole of media; M1 and M2 = branches of media; R1 = anterior branch of radius; R4+5 = posterior branch of radius; sc = subcosta; ta = anterior transversal (= crossvein rm); tb = basal transversal.

area, covered with trichia. Mid tibia with row of small, close set anterior bristles and a few posterior and posterodorsal bristles. Hind tibia with a few large anterior bristles; some large posterodorsal bristles; several small, close-set bristles in one row posterodorsally; tibial comb consisting of triangular area, densely covered with long microtrichia posteroapical and complete transverse row of setae along apical margin ( Fig. 4 J). Fore tarsus without distinct spine-like setae ventrally. Empodia ( Fig. 4 H) rudimentary, thread like.

Abdomen ( Fig. 2 ). Pale abdominal markings present along posterior margin of tergites; more or less extended anteriorly to form larger triangular or complete pale areas laterally. Preterminal segments often darker than rest of abdomen.

Male terminalia ( Figs 5 A&B). Tergite IX medium sized, wide to long rectangular, more or less divided mesally, usually with sclerotized mesal suture; scattered with setae that get larger towards apicolateral corners, without any outstanding strong setae. Cercus small ovate knob; scattered with small, thin setae. Gonocoxite ( Fig 5 B) large, moderately to deeply incised ventrally in which a usually bud-shaped, strongly sclerotized hypandrial lobe is situated; apically divided into an outer wall (section II) and a medioventral, inner wall (section III). Epiproct ( Fig. 5 B) pointed triangular, very hyaline, without setae. Hypoproct ( Figs 5 B, 6C) usually forming long tapered posterior process, straight or downcurved. Lateral margin of tergite X forming slender, setose pseudocercus; clearly articulated against rest of segment; of variable length. Aedeagus ( Fig. 5 B) elongated, hyaline, tapered apically, well retracted within gonocoxite, basally jointed with strong gonocoxal apodemes. Aedeagal guides ( Figs 5 B, 6A) large, hyaline lobes; rectangular or elongated; situated dorsolaterad of hypandrial lobe. Hypandrial lobe ( Fig. 5 B) well developed, usually bud-shaped, of medium size and strongly sclerotized; its angle in relation to gonocoxite variable, usually exposed and aligned with gonocoxite, sometimes retracted into gonocoxite and produced interodorsad; basolaterally with patch of placoid sensillae; with a small split apicomedially. Gonostylus divided into six branches ( Fig. 5 A). Dorsal branch short with smooth whitish rounded tip or moderately to extremely elongated; without blunt lamellae; lateral surface always covered with strong setae. Dorsointernal branch usually present as a fan-shaped outgrowth of the ventrointernal margin of the dorsal branch; with row of small, blunt lamellae along entire internal margin; without setae, sometimes reduced to bifurcated or small bare knob ( Fig. 14 B). Medial branch reduced, present as small to large knob, with a few setae. Ventral branch large, usually shaped as a thin spatulate plate, sometimes elongated, lanceolate; typically with a few characteristically fan-tipped setae ventrolaterally and some strong setae apicomedially. Anterior branch forming ventrally directed, subrectangular to triangular cushion; without setae, sometimes with numerous small, blunt projections caudally ( Fig. 14 B). Internal branch forming medium sized, bulbous, largely striated pouch; posteriorly with a few setae, sometimes with a small, digitate lobe ( Fig. 14 B).

Female terminalia ( Fig. 5 C). Usually partly retracted within tergite VII. Tergite VIII well developed, subrectangular, devoid of setae. Sternite VIII large; ventrally scattered with small setae; fused with a welldeveloped, apically truncated or pointed gonocoxite VIII, bearing several strong setae along apical margin. Gonapophysis VIII present as hyaline tapered protrusion, usually extending beyond apex of gonocoxite VIII, without setae. Labia not discernible, or fused basally with gonapophysis VIII. Tergite IX well developed and partly fused with gonocoxite IX, without setae. Spermathecal duct ending in constricted, sclerotized eminence. Tergite X reduced or fused with epiproct. Sternite X apparently fused basally with gonapophysis IX; forming a stout, sclerotized, elongated postgenital plate; apically covered with small setae. Cercus one- or two-segmented, scattered with small setae; elongated to moderately truncate; apical segment when present short, ovate.

Larva unknown.

Notes on biology. Little is known about larval habitats of Pseudexechia . P. trisignata s. l. has been reared from soft gill fungi like Naucoria sp. and Galerina sp. ( Chandler 1993) and Psathyrella piluliformis ( Sasakawa & Ishizaki 1999) . P. tristriata has been reared from Thelephora terrestris ( Yakovlev 1994) . P. trivittata has been reared from fruiting bodies of coprophilous agarics like Coprinus , Psathyrella and Panaeolus ( Jakovlev et al. 2008) . Adults of Pseudexechia were mainly collected with aspirator in caves in wintertime (55%) (see Kjaerandsen 1993), with window traps (29%) or with sweep net (10%). It is noteworthy that although large Malaise trap collections have been examined in search of Pseudexechia , only about 1% of the examined material originates from Malaise trap collections. This under-representation in Malaise trap collections seems to hold for several of the Exechiini genera, and might be explained by a general negative phototaxis for many members of the tribe.

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 4. Morphology of Pseudexechia [A – D + F – J = P. trisignata (Edwards, 1913), E = P. pectinacea (Ostroverkhova, 1979)]. — A. Head in dorsal view. — B. Antenna, dorsal view. — C. Antenna, lateral view — D. Segment III – V of maxillary palp. — E. Face enlarged. — F. Thorax, lateral view. — G. Fore tarsus V. — H. Mid tarsus V. — I. Hind tarsus V. — J. Apex of hind tibia, medial view. Abbreviations: anepist = anepisternum; clyp = clypeus; cx 1 = forecoxa; cx 2 = midcoxa; cx 3 = hindcoxa; emp = empodium; fc = face; flag I = first flagellar segment; flag II = second flagellar segment; fr fur = frontal furrow; fr tub = frontal tubercle; htl = halter; ltg = laterotergite; m oc = medial ocellus; mtg = mediotergite; proepist seta = proepisternal seta; sc = scutum; sctl = scutellum; sens pit = sensory pit; t comb = tibial comb.

FIGURE 5. Morphology of terminalia of Pseudexechia. — A. Male gonostylus of P. trisignata (Edwards, 1913), internal view. — B. Male terminalia of P. pectinacea (Ostroverkhova, 1979), caudal view with gonostyles removed. — C. Female terminalia of P. canalicula (Johannsen, 1912), lateral view. Abbreviations: a br = anterior branch of gonostylus; aed = aedeagus; aed gd = aedeagal guide; cerc = cercus; d br = dorsal branch of gonostylus; d cond = dorsal condyle; di br = dorsointernal branch of gonostylus; epi = epiproct; gc ap = gonocoxal apodeme; gc II = section II of gonocoxite; gc III = section III of gonocoxite; gc = gonocoxite; gp = gonapophysis; hyp = hypoproct; hyp lb = hypandrial lobe; i br = internal branch of gonostylus; j scl = joint sclerite; m br = medial branch of gonostylus; pseudocerc = pseudocercus; sens basicon = basiconic sensillae; st = sternite; tg = tergite; v br = ventral branch of gonostylus; v cond = ventral condyle.

FIGURE 6. Pseudexechia trisignata (Edwards, 1913). — A. Male terminalia, ventral view. — B. Male gonostylus, internal view. — C. Male tergite IX and cerci, dorsal view. — D. Female terminalia, lateral view.

FIGURE 14. Pseudexechia tristriata (Stackelberg, 1969). — A. Male terminalia, ventral view. — B. Male gonostylus, internal view. — C. Male tergite IX and cerci, dorsal view. — D. Female terminalia, lateral view.