Chaoborus posio Salmela & Härmä & Taylor 2021, sp. n.

Chaoborus posio Salmela sp. n.

Material examined. Type material. Holotype. Male. [“http://tun.fi/” “ NVO.LMM-el-164” “ FINLAND Posio ” “ Peuralamminharjut ” “etrs-tm35fin: 7350437,” “527225” “ 23.V.2019 ” “ Salmela, Jukka leg.”] [QR code], printed. Type locality: Finland, Ks: Posio, Peuralamminharjut, 66.27269 27.60633, 311 masl, e.l., larval skin and pupal exuviae in Euparal and adult pinned, NVO.LMM-el-164 (LMM).

Paratypes. Finland. Ta: Tammela, Saarijärvi S, Salmela J. leg. 3. V.2020, 10 larvae, NVO. LMM-el-20-7; 1 male pupa e.l., NVO. LMM-el-20-24; 1 female e.l., NVO. LMM-el-20-33; 1 female e.l., NVO. LMM-el-20-35; 1 male pupa e.l., NVO. LMM-el-20-36; 1 male e.l., NVO. LMM-el-20-37; 1 female e.l., NVO. LMM-el-20-38; 1 male e.l., NVO. LMM-el-20-59; 1 female e.l., NVO. LMM-el-20-60; 1 female e.l., NVO. LMM-el-20-61; 1 female e.l., NVO. LMM-el-20-62 (LMM); Härmä O. leg. 21.IV.2020, 4 larvae, LG.6201; 1 female e.l., LG.6271; 1 male e.l., LG.6272; 1 male e.l., LG.6284 (FLHM). Ok: Suomussalmi, Hoiluankangas, Salmela J. leg. 22.5.2019, 10 larvae, NVO. CUL-2019-9; 1 larva, head & tail on slide, BOLD, NVO. CUL-2019-80; 1 larva, head & tail on slide, BOLD, NVO. CUL-2019-81 (LMM). Ks: Posio, Peuralamminharjut, Salmela J. leg. 23.5.2019, 1 male e.l., larval and pupal exuviae on slide, legs, wings, head, hypopygium on slide, NVO. LMM-el-134; 1 male e.l., larval and pupal exuviae on slide, legs, wings, head, hypopygium on slide, NVO. LMM-el-135; 1 male e.l., larval and pupal exuviae on slide, legs, wings, head, hypopygium on slide, NVO. LMM-el-137; 1 female e.l., larval and pupal exuviae on slide, NVO. LMM-el-138; 1 male e.l., larval and pupal exuviae on slide, hypopygium on slide, NVO. LMM-el-141 (LMM); 1 male e.l., pinned, larval and pupal exuviae on slide, NVO. LMM-el-142; 1 male e.l., pinned, larval and pupal exuviae on slide, LMM-el-142 (LMM); 1 male e.l., NVO. LMM-el-170 (MZH); 1 male e.p., NVO. LMM-el-175 (LMM); 1 pupa e.l., larval exuviae on slide, NVO. LMM-el-136; 1 male pupa e.l., larval exuviae on slide, NVO. LMM-el-139; 1 female, larval and pupal exuviae on slide (adult escaped during rearing) e.l., NVO. LMM-el-140; 1 female, larval and pupal exuviae on slide, NVO. LMM-el-143; 1 male e.l., larval and pupal exuviae on slide, legs, wings, head, hypopygium on slide, NVO. LMM-el-144; 1 male e.l., larval and pupal exuviae on slide, legs, wings, head, hypopygium on slide, NVO. LMM-el-145; 1 female e.l., larval and pupal exuviae on slide, NVO. LMM-el-146; 1 male e.l., pinned, NVO. LMM-el-162; 1 male e.p., NVO. LMM-el-184; 1 female e.p., NVO. LMM-el-185; 1 male e.p., NVO. LMM-el-186; 1 male e.p., NVO. LMM-el-188; 1 male e.p., NVO. LMM-el-193; 1 female e.p., NVO. LMM-el-194; 1 male e.p., NVO. LMM-el-195; 3 males 1 female e.p., parameres of one male in glue on slide, NVO. LMM-el- 199; 1 female e.p., NVO. LMM-el-202; 2 males 2 females e.p., NVO. LMM-el-203. 24.5.2018, 20 larvae 5 pupae, NVO. ins2018-384; 7 pupae, NVO. ins2018-386; 15 larvae, NVO. ins2018-387; 1 larva, BOLD, NVO. ins2018-580; 1 larva, BOLD, NVO. ins2018-581; 1 larva, BOLD, NVO. ins2018-582; 1 pupa, BOLD, NVO. ins2018-616; 1 pupa, BOLD, NVO. ins2018-617; 1 pupa, BOLD, NVO. ins2018-618; 1 larva, BOLD, NVO. ins2018-619; 1 larva, BOLD, NVO. ins2018-620; 1 larva, BOLD, NVO. ins2018-621; 1 larva, BOLD, NVO. ins2018-622; 1 larva, BOLD, NVO. ins2018-623; Salmela J. & Ahola J. leg. 20.VIII.2019, 4 larvae, NVO. LMM-el-599; (LMM). Obb: Rovaniemi, Montosenlampi W, Salmela J. leg. 5. VI.2020, 2 male e.p., NVO. LMM-el-20-104; 1 male e.p., adult pinned, pupal exuviae on slide, NVO. LMM-el-20-109; 1 male e.p., NVO. LMM-el-20-111; 1 male e.p., NVO. LMM-el-20-112; 1 female e.p., NVO. LMM-el-20-113; 7 male e.p., NVO. LMM-el-20-114 (LMM); 1 larva, 2 males and pupa exuviae (ABC) Lkoc: Kittilä, Muotrikkilehto, Salmela J. leg. 27.VII.2019, 1 larva, head and tail on slide, BOLD, NVO. LMM-el-574; 3 larvae, NVO. LMM-el-588; 1 larva, NVO. LMM-el-589; 5 larvae, NVO. LMM-el-590; 3 larvae, NVO. LMM-el-600; 1 larva, NVO. LMM-el-612; 1 larva, BOLD, NVO. CUL-2019-75 (LMM). Li: Inari, Latnabuolza, Salmela J. leg. 23.8.2019, 1 larva, NVO. LMM-el-584; 1 larva, NVO. LMM-el-606; 1 larva, head & tail on slide, BOLD, NVO. CUL-2019-76 (LMM). Inari, Iso-Söimi, Salmela J. leg. 29. VI.2020, 6 larvae, NVO. LMM-el-20-137 (LMM). Utsjoki, Geaidnogeachi, Salmela J. leg., 13.6.2019, 1 male e.p., NVO. LMM-el-306 (LMM); 1 male pupa e.l., NVO. LMM-el-293; 1 female pupa e.l., NVO. LMM-el-294; 1 male e.l., larval and pupal exuviae on slide, hypopygium on slide, NVO. LMM-el-295; 1 male e.l., larval and pupal exuviae on slide, hypopygium on slide, NVO. LMM-el-296; 1 female e.l., larval and pupal exuviae on slide, NVO. LMM-el-297; 1 pupa e.l., NVO. LMM-el-299; 1 male e.l., larval and pupal exuviae on slide, legs, wings, head, hypopygium on slide, NVO. LMM-el-302; 2 males 2 females e.p., NVO. LMM-el-307; 1 male e.p., NVO. LMM-el-309; 1 female e.l., NVO. LMM-el-310; 1 female e.l., NVO. LMM-el-311; 1 female, NVO. LMM-el-312; 1 male pupa e.l., NVO. LMM-el-313; 1 male e.l., larval and pupal exuviae on slide, legs, wings, head, hypopygium on slide, NVO. LMM-el-314; 1 female e.l., NVO. LMM-el- 315; 1 female pupa e.l., NVO. LMM-el-316; 1 female e.l., NVO. LMM-el-317; 1 male pupa e.l., NVO. LMM-el-318; 1 female pupa e.l., NVO. LMM-el-319; 1 male e.p., NVO. LMM-el-320; 1 male e.p., NVO. LMM-el-321; 1 male e.p., NVO. LMM-el-323; 1 female e.p., NVO. LMM-el-324; 1 male e.p., NVO. LMM-el-326; 1 female e.p., NVO. LMM-el-327; 1 female e.p., NVO. LMM-el-328; 1 male e.p., NVO. LMM-el-329; 1 male e.p., NVO. LMM-el-330; 1 female e.p., NVO. LMM-el-331; 3 male 3 female e.p., NVO. LMM-el-339; 4 males e.p., NVO. LMM-el-340; 1 female e.p., NVO. LMM-el-343; 1 male e.p., NVO. LMM-el-344; 1 female e.l., NVO. LMM-el-365; 4 males 3 females e.p., NVO. LMM-el-372; 2 males e.p., NVO. LMM-el-379; 1 male e.p., hypopygium on slide, NVO. LMM-el-583; 17.VII.2018, 1 larva, BOLD, NVO. ins2018-480 (LMM).

Derivatio nominis. The name of the new species refers to Posio, a municipality in southeastern Lapland. Posio is derived from Sámi languages (boaššu), meaning a sacred opening opposite of the main entrance in lavvu (a tentlike dwelling). The name is a noun in apposition.

Diagnosis. General coloration of adult specimens dark–almost black. Male hypopygium mostly dark, gonocoxite and gonostylus relatively wide; paramere strongly scleroterized, apical beak long, almost straight. Respiratory organs of pupa club-shaped, widest medially, not constricted subapically. Larval mandible with conspicuous lateral teeth, uppermost about as large as subordinate tooth; number of mandibular fan bristles over 20 (21–29).

Description. Adult male. Head dark with dark setae. Non–setose area of occiput pale, frontal macula bare. Clypeus with numerous dark setae. Antennal flagellomeres slightly infuscated between bases of whorls and apices, basal parts of flagellomeres pale; length of penultimate flagellomere 242 (233–256), apical flagellomere 201 (188–222, n=5), penultimate/apical 1.21 (1.05–1.36). Lengths of palpal segments 2–5: 104 (90–113, n=6), 213 (191–239, n=6), 180 (174–186, n=6), 320 (295–330, n=5). Thorax mostly dark–almost black (Fig. 13). Scutum dark brown–black, scutellar stripes are dark and hard to discriminate expect their non–setosity (Fig. 13b); narrow pale area is present along paranotal suture and anepisternum (Fig. 13a). Scutellum and mediotergite black. Halter whitish. Thoracic setae (n=2): antepronotal lobe 33–34, postpronotal 5–6, proepisternal 5–6, katepisternal 3–5, anepisternal 10–12, anepimeron 5–7, supra–alar 1. Legs pale brown–brown, apices of femora slightly darkened. Foreleg, lengths of fe, ti and ta1–ta5 (n=7): fe 1706 (1653–1778), ti 1889 (1778–2000), t1 875 (807–945), t2 552 (523–591), t3 464 (432–500), t4 299 (278–326), t5 207 (194–225). Midleg, lengths of fe, ti and ta1–ta5 (n=7): fe 1606 (1489–1917), ti 1599 (1486–1917), t1 805 (716–1139), t2 496 (432–695), t3 383 (336–466), t4 247 (225–284), t5 195 (183–217). Hind leg, lengths of fe, ti and ta1–ta5 (n=7): fe 1880 (1806–1972), ti 1815 (1458–1972), t1 1086 (972–1222), t2 641 (580–739), t3 458 (409–517), t4 275 (245–330), t5 200 (188–214). Wing (n=5, Fig. 4b). Length 3655 (3440–3859), width 797 (714–847), length/width 4.59 (4.45–4.82); fork of R 2+3 480 (422–531), fork of M 1+2 442 (391–484), R 3 1063 (954–1129), M 1 926 (862–971), number of setae on squama 35 (26–45, n=7). Abdomen dark–almost black. Hypopygium dark brown, epandrium rounded apically (Fig. 14a). Gonocoxite stout, bearing dark setae, length 571 (472–625), width 217 (186–239), length/width 2.64 (2.40–3.03, n=10); gonostylus relatively stout, length 495 (466–545), width, 53 (48–59), length/width 9.43 (7.90–10.69); paramere (Fig. 14 b–e) strongly sclerotezited, dark, apical claw rather long and straight; length 179 (160–194, n=9).

Adult female. In general, similar to male. Penultimate flagellomere 144–153 (n=2), apical flagellomere 151 (n=1). Lengths of palpal segments 2–5: 98–207, 153–300, 85–176, 171–295 (n=2). Thoracic setae (n=2): antepronotal lobe 20–22, postpronotal 4–6, proepisternal 4, katepisternal 5–8, anepisternal 14–15, anepimeron 10–13, supra–alar 1. Wing length 3647–3898, width 947–1043, length/width 3.73–3.85 (n=2); fork of R 2+3 483–539, fork of M 1+2 408–454, R 3 1274–1336, M 1 1154–1231 (n=2), number of setae on squama 31 (n=1). Foreleg, lengths of fe, ti and ta1–ta5 (n=2): fe 1611–1651, ti 1744–1768, t1 819–850, t2 482–498, t3 403–453, t4 267–299, t5 202–206. Midleg, lengths of fe, ti and ta1–ta5 (n=2): fe 1550–1579, ti 1476–1479, t1 722–748, t2 420–458, t3 322–360, t4 232–234, t5 189–197. Hind leg, lengths of fe, ti and ta1–ta5 (n=2): fe 1890–1916, ti 1858–1870, t1 1032–1147, t2 586–661, t3 430–466, t4 270–292, t5 196–198.

Pupa. Thoracic respiratory organ rather short, club–shaped, widest medially, not constricted subapically (Fig. 9d); length 844 (773–925), width 243 (214–284), length/width 3.48 (2.92–4.0, n=18). Lateral ribs of terminal processes slightly paler than middle rib.

IV instar larva. Total length circa 12 mm. Anal fan setae 26 (24–28, n=17). Anal hook brown–dark brown in color. Mandibular fan bristles 24 (21–29, n=25, Fig. 10h). Lateral teeth of mandible conspicuous, ultimate tooth about as large as mandibular tooth 3 (Fig. 10f); number of lateral teeth 6.32 (5–8, n=25); mandibular teeth 1–4 darkened along entire length. Labral blade moderately serrated, basal part relatively wide (Fig. 10g), usually darkened; length 268 (228–295, n=25), width 73 (56–84, n=24), length/width 3.7 (3.0–5.0, n=24). Length of antenna 587 (545–682, n=24).

DNA barcoding. Chaoborus posio sp. n. was also very divergent from other members of the complex (>17%) (Table 1). Intraspecific variation was the lowest for the species complex (Table 1), perhaps indicating that this species survived in a single glacial refugium. Because the within species divergence was weak, the probability of identification from barcoding information was the highest in the complex (>99%). The barcoded specimens formed a unique BIN cluster in BOLD (BOLD:ADT7562).

Comments. The new species can be readily separated from C. flavicans and C. albipes in larval, pupal and adult stages. Fourth instar larvae possess a high number, in most cases well over 20 mandibular fan bristles; the number of such bristles is lower in the other species (the averages for C. flavicans and C. albipes are 13 and 17.7, respectively). The labral blade of the new species is rather wide: length/width ratio is ca. 3.72, whereas 5.55 and 4.73 in C. albipes and C. flavicans, respectively. The respiratory organ of pupae is not constricted subapically and it is generally rather short and wide. Adults are very darkly colored, almost black, and the thoracic setae are dark. Dark forms of C. albipes have a more pale/whitish coloration on the scutum and the thoracic setae are pale. The gonocoxite and gonostylus of the adult male in C. posio sp. n. are very stout, (i.e., they are more slender in the other species), and the paramere is strongly sclerotized. The apical claw is long and almost straight.

Distribution. Hitherto known from Finland only, but is likely to occur at least in Sweden, Norway and northwestern Russia. Most of the records are from the north boreal ecoregion, yet there is a locality in the south boreal zone, ca. 500 km south of the main area of distribution. It is not yet known if this should be considered a relict population outside of the normal range, or if the species is more widely present in the southern parts of Fennoscandia. The northernmost sites are presently at the subarctic zone, north of the limit of coniferous trees.

Ecology. The life cycle is univoltine, i.e., there is one generation per year. Overwintered, IV instar larvae pupate readily under laboratory conditions at room temperature, and the flying season in nature takes place in early summer. IV instar larvae of the new generation are present by mid-August. Larvae have been collected from fishless, permanent ponds (n=10, plus 8 sites detected in late 2020, J. Salmela et al. in prep). These ponds are often rather large (mean area 3400 m 2) and the larvae are absent from smaller yet permanent ponds that are present nearby. Typically the water color is at least moderately humic and the shores are characterized by bog vegetation. The new species often co-occurs with C. obscuripes, occasionally with C. flavicans (three occasions) and C. albipes (two occasions). In Central Lapland, Kittilä, C. posio sp. n. was observed from a possibly alkaline pond with clear water; the pond is surrounded by a calcareous rich fen vegetation.