Bilyjomyia, Niitsuma, Hiromi & Watson, Charles N., 2009

Niitsuma, Hiromi & Watson, Charles N., 2009, Bilyjomyia, a new genus of the tribe Macropelopiini from the Holarctic (Diptera: Chironomidae), Zootaxa 2166, pp. 57-68 : 58-62

Bilyjomyia new genus

Type species: Tanypus algens Coquillett, 1902 , by present designation.

Etymology. The new genus is named after Mr. Bohdan Bilyj, in recognition of his contributions to chironomid taxonomy and systematics.

Diagnosis. Male: Anterior abdominal tergites pale, contrasting with dark brown posterior tergites and hypopygium. Antenna with 14 flagellomeres. Occasionally small scutal tubercle present; postnotals present. Wing banded. Foreleg without tibial comb; pulvilli large. Tergite IX with few setae confined to its posterior margin; gonostylus greater than 0.5 length of gonocoxite, with long and nearly parallel-sided distal arm ending in blunt apex bearing megaseta.

Female: Abdominal tergites uniformly colored. Antenna with 14 flagellomeres. Antepronotals in two groups. Wing banding more extensive than in male. First tarsomere with sensilla chaetica on mid- and hind legs. Seminal capsule ovoid, with prominent neck placed symmetrically; coxosternapodeme nearly straight; Gp VIII broadly triangular, produced caudomesially.

Pupa: Thoracic horn broad, flattened and spinulate on surface; plastron plate with 3 prominent aeropyles on basal margin. Tergite I with pigmented scar. Tergites II–VII with spiniform D1; T.III–V with D2 and D3 taeniate and apically hooked; A.VII and VIII each with 5 LS-setae. Anal lobes longer than broad, with spines on inner margin.

Larva: Labrum with small sclerite. Ventral cephalic seta S9 anteromedial to S10; S9 and SSm multibranched, S10 simple. M appendage with petiolate labial vesicles; pseudoradula with granulation in apical half only. Dorsomental plates with 6–8 moderately sized teeth; inner margin rounded, not extending to pseudoradula. Pecten hypopharyngis with innermost tooth broadened. Posterior parapod with two small claws depressed and expanded basally.

Description. Male. Body length 4.8–6.4 mm; wing length 3.2–4.4 mm.

Coloration. Head pale to light brown. Thorax pale to brown with darker vittae and pleural sclerites. Wing banded by black macrotrichiae. Legs mostly pale. Abdomen distinctively patterned; anterior tergites pale, contrasting with mostly brown posterior tergites. Gonostylus and gonocoxite brown.

Head. Antenna with 14 flagellomeres; apical flagellomere weakly separated, with subapical seta; AR 1.9–2.0. Eye with dorsal extension. Temporals multiserial.

Thorax. Antepronotum well developed, with broad medial notch. Occasionally scutum with small dorsomedial tubercle. Antepronotals in one lateral group; pteropleurals, mesosternals and postnotals present.

Wing. Membrane with dense macrotrichiae. Costa produced well beyond R4+5; MCu joining M3+4 just distal of FCu.

Legs. Tibial spurs bearing 15–20 side teeth. Foreleg without tibial comb; hind leg with well-developed tibial comb. Tarsal claws pointed, with 2–5 short spines arising from basoventral margin; pulvilli well developed.

Abdomen. Tergite IX not enlarged, with 1–8 setae inserted on posterior margin. Gonocoxite simple, evenly setose. Gonostylus greater than 0.5 length of gonocoxite, sharply angled near base; distal arm nearly parallel sided for most of its length, with fine longitudinal ridges, ending in blunt apex. Phallapodeme with or without strong bend near mesial end; membranous aedeagal lobe compact with group of spines.

Female. Body length 3.8–4.7 mm; wing length 3.3–4.4 mm.

Coloration. Abdominal tergites uniformly colored, pale or brown. Wing banding more extensive than in male.

Head. Antenna with 14 flagellomeres; AR 0.23–0.27.

Thorax. Antepronotal setae in two groups, dorsolateral and lateral.

Legs. First tarsomeres of mid- and hind legs with sensilla chaetica in apical 0.05–0.10.

Abdomen. Seminal capsule ovoid, widest near middle, with prominent neck placed symmetrically, partially or completely infuscated. Coxosternapodeme mostly straight, curved only near union with ramus. Segment X sometimes with few setae at corners; Gp VIII broadly triangular, moderately produced caudomesially.

Pupa. Body length 6.0–9.0 mm.

Coloration. Brown. Abdominal segments lighter laterally and posteriorly.

Cephalothorax. Thorax rugose dorsally. Thoracic seta Dc1 robust with pointed apex, granulose in distal half; Dc2 very short; Sa longer than Dc1. Thoracic horn flattened, broadening rapidly from base, with numerous spines on surface. Plastron plate broadly oval to trapezoidal, often with distal margin concave, occupying distal 0.4–0.5 of horn; base of plastron plate with 3 aeropyles, smallest located medially, larger one on either side. Tracheae usually visible, extending through horn sac to base of plastron plate; internal rods absent.

FIGURES 6–21. Bilyjomyia fontana new genus, new species, pupa (6–10) and larva (11–21). 6, thoracic horn; 7, thoracic setae; 8, abdomen, dorsal view; 9, abdominal segment I, dorsal view; 10, shagreen on posteromedial part of abdominal tergite IV; 11, head with chaetotaxy, dorsal view (R) and ventral view (L); 12, labral region, dorsal view; 13, showing distance between two labral setae S2 (D) and width of labral sclerite (W); 14, antenna; 15, apex of antenna; 16, mandible; 17, maxillary palp with apical stylets; 18, dorsomental plate; 19, ligula and paraligula; 20, pecten hypopharyngis; 21, claws of posterior parapod. Abbreviations: CP, coronal sensory pore; Dc1, 2, dorsocentral setae 1, 2; DP, dorsal sensory pore; S1–11, cephalic setae 1–11; Sa, supraalar seta; SSm, seta submenti; VP, ventral sensory pore.

Abdomen. Scar on T.I more or less distinct. Shagreen mainly consisting of serial rows of 2–5 spinules. D1- setae on T.II–VII spiniform, 0.2–0.4 times as long as segment, arising from small tubercles; D2- and D3-setae on T.III–V taeniate, apically hooked, 0.4–0.7 times as long as segment, arising from small tubercles; remaining D- setae short and hair-like. Segment VII with 5 LS-setae inserted laterally on about posterior 0.5 of segment; LS1-seta set off from others located equidistantly from each other. Segment VIII with 5 LS- setae inserted laterally on posterior 0.3–0.4 of segment. Anal lobe 2.5–3.0 times as long as broad; inner margin with fine spines; outer margin with 2 macrosetae, and fringe of fine setae gradually shortening towards apex.

Fourth instar larva. Total length 6.2–11.6 mm.

Coloration. Head capsule with light brown occipital margin.

Head. Cephalic index 0.70–0.80. Cephalic setae S1–S9 and SSm multi-branched, S10 simple and 2.0–2.5 times as long as S9, S11 not discernable; S8 anterolateral to dorsal sensory pore and near to S7; S9 anteromedial to S10. Labral region with small sclerite anterior to labral rod, nearly circular to amoebiform, occasionally fragmented, and with characteristically irregular surface. Antenna with 4 segments, 1.2–1.4 times as long as mandible; AR 6.8–8.7. First segment with ring organ located 0.77–0.82 from base; blade shorter than flagellum. Second segment with style about 1.5–1.9 times as long as peg sensilla, these arising from its side. Third segment slightly longer than wide, subequal to segment 4, and subtended by membranous stalk. Basal segment of maxillary palp with ring organ basally. Mandible evenly curved, with basal tooth appressed and apically bifid; ventrolateral seta 1 simple, ventrolateral setae 2 and 3 multi-branched. Dorsomental plate with 6–9 teeth; outermost tooth usually much smaller than others; inner margin of plate rounded, not reaching pseudoradula. M appendage with petiolate lateral vesicles; pseudoradula with granulation in distal half only, not expanded apically. Ligula with 5 teeth, toothed margin concave; paraligula bifid, with inner tooth small, about as long as wide, often appressed to outer tooth and difficult to see. Pecten hypopharyngis with innermost tooth, and sometimes next, broadened.

Body. Abdominal segments I–VII with lateral fringes of sparse setae. Procercus bearing 8 anal setae. Two pairs of conical anal tubules present; dorsolateral pair about 3 times as long as its basal width, ventrolateral pair about 2/3 times as long as dorsolateral pair. Posterior parapods with 11 large and 5 smaller claws; some large claws with fine spines along inner margin, two small claws distinctly depressed with expanded bases.

Remarks. Because of the depressed posterior parapod claws with expanded bases, the larva will not key past couplet 13 in Fittkau & Roback (1983). The pupa will key to Macropelopia in Fittkau & Murray (1986). Couplet 12 in the Murray & Fittkau key (1989) to adult males presents a problem, due to the variable scutal tubercle. If a scutal tubercle is discernable, the male of Bilyjomyia will key to Bethbilbeckia ; if absent or obscured, the male will key to couplet 16, but will not fit either alternative ( Apsectrotanypus or Radotanypus Fittkau et Murray). The female will key to Natarsia Fittkau and Macropelopia (part) in Saether (1977).

The basal segment of the larval maxillary palp with a ring organ near the base, and the pseudoradula with granulation restricted to the distal half, are also found in Bethbilbeckia and Macropelopia , and set the larvae of these genera apart from those of other Macropelopiini . However, Bilyjomyia larvae differ from all other known Macropelopiini in the distinctive labral sclerite, and the relative positions and state of the S9- and S10- setae. The S9-seta multi-branched and anteromedial to a simple S10 is unique among Macropelopiini . Most Macropelopiini have the S9-seta simple and directly anterior or anterolateral to a simple S10 ( Kowalyk 1985). Apsectrotanypus johnsoni (Coquillett) , Apsectrotanypus yoshimurai (Tokunaga) , Alotanypus kuroberobustus (Sasa et Okazawa) and Brundiniella yagukiensis Niitsuma , have S10 multi-branched. However, the S9 is simple in Brundiniella yagukiensis ( Niitsuma 2003) and multi-branched in the other three species ( Niitsuma 2004, 2005; Watson, personal observation). The two depressed posterior parapod claws with expanded bases will separate Bilyjomyia larvae from all other known Macropelopiini except Brundiniella Roback , and an Australian species, Apsectrotanypus pallipes (Freeman) ( Horne & Pettigrove 1989) . The inner margins of the dorsomental plates are rounded, contrasting with those of Bethbilbeckia and Brundiniella , which have an inner projection reaching the pseudoradula.

In the general form of the thoracic horn, the shape and armature of the anal lobes, the scar of T.I, abdominal setation, and shagreen, the pupa is identical to those of the Macropelopia notata group. Bilyjomyia pupae can only be distinguished from them by the prominent aeropyles at the base of the plastron plate.

The adult males of Bilyjomyia can be separated from all other known Macropelopiini by the distinctive color pattern of the abdomen, the small number of setae on T.IX, and the restriction of those setae to the posterior margin of the tergite. Unlike the immatures, there is little in the morphology of the adult male to suggest a close relationship to Bethbilbeckia and Macropelopia . The form of the gonostylus is unlike that of those genera. It more closely resembles the gonostylus of Brundiniella , Derotanypus Roback , Fittkauimyia Karunakaran , Psectrotanypus Kieffer and Radotanypus. Bilyjomyia algens males may have a very small scutal tubercle. It is easily obscured by setae or distortion of the thorax in mounting. To date, it has not been observed in Bilyjomyia fontana . The male lacks the foreleg tibial comb found in Macropelopia and Alotanypus Roback. Bilyjomyia adults have prominent pulvilli, a feature shared with Apsectrotanypus , Brundiniella , Fittkauimyia , Psectrotanypus and Radotanypus, but not found in Bethbilbeckia or Macropelopia .

Bilyjomyia females can only be separated from those of other Macropelopiini by a combination of characters. Among the genera with prominent pulvilli, Apsectrotanypus , Brundiniella and Psectrotanypus also have banded wings, but the pattern of markings cannot be confused with that of Bilyjomyia species (see Cheng & Wang 2006; Niitsuma 2003, 2004; Roback 1971).

Bilyjomyia females have sensilla chaetica confined to the apical 0.05–0.10 of the first tarsomeres of the mid- and hind legs. Females of Brundiniella eumorpha (Sublette) , Alotanypus aris Roback , Apsectrotanypus johnsoni and Radotanypus florens (Johannsen) are similar to those of Bilyjomyia in having sensilla chaetica confined to the apical 0.1 or less of the first tarsomeres of the mid- and hind legs (Watson, personal observation). The Japanese species Apsectrotanypus yoshimurai , Alotanypus kuroberobustus and Brundiniella yagukiensis are similar in this respect ( Niitsuma 2004, 2005 in the former two species, personal observation in the last species).

Allowing for variation in mounting, there do not appear to be significant differences in the form of Gp VIII between females of Bilyjomyia , and those of Apsectrotanypus , Bethbilbeckia , and Macropelopia . The Gp VIII of North American Psectrotanypus species is more rounded and not as strongly produced. The coxosternapodeme usually appears more evenly curved in the latter genera, but the difference is subtle and influenced by variation in mounting (Watson, personal observation).