Diamesa gregsoni Edwards

Semenchenko, Alexander A. & Makarchenko, Eugenyi A., 2025, On the taxonomy and distribution of Diamesa gregsoni Edwards, (Diptera: Chironomidae: Diamesinae), with morphological redescription and DNA barcoding of species from the Far East, Zootaxa 5636 (3), pp. 499-510 : 503-508

Diamesa gregsoni Edwards

( Figs 7–25 )

Diamesa gregsoni Edwards, 1933: 618 ; Serra-Tosio 1967: 93, 1971: 145; Hansen & Cook 1976: 91; Makarchenko 1985: 93, 2006: 266, 474, 614; Ashe & O’Conner 2009: 276.

Material examined. JAPAN: 1 adult male, Hokkaido, Supporo, Jozenkei , 05.IV.1990, leg. Makarchenko. RUSSIA: 4 pharate adult males, extracted from mature pupae, 3 larvae, Magadan Region, Olsky District, Ola River , 127 km, 22.XI.2013, leg. E. Khamenkova ; 6 adult males the same data, except 137 km below the bridge, 60.412194 N, 151.514564 E, 29.04– 13. V.2017, leg. E. Khamenkova ; 5 larvae, Kamchatka Territory, Yelizovsky District, Paratunka River , 52.87888 N 158.20930 E, 18.IX.2022, leg. A. Semenchenko ; 5 adult males, 3 pharate adult males extracted from mature pupae, 4 pupae, 6 larvae, Khabarovsk Territory, Solnechny District, the vicinity of the Gorny Village , Levaya Silinka River , 11. V.1984, leg. E. Makarchenko ; 1 adult male, the same data, except Nanaisky District, Anyuisky National Park, Pikhtsa River (tributary of Gassi Lake ), Amur River basin, 48.796733 N, 136.783783 E, 26. V.2020, leg. Yavoskaya ; 5 larvae, the same data, except Tuguro-Chumikansky District , 53.675535 N, 137.040644 E, 10.VIII.2022, leg. N. Yavorskaya ; 5 adult males, Sakhalin Island, Noglikskyi District, Chamginsky Pass , Khrebtovyi Stream , 50.758757 N, 143.285754 E, alt. 743 m a.s.l., 28.VII.2003, leg. E. Makarchenko.

Description

Adult male (n =8, except when otherwise stated). Total length 4.3–5.2 (4.7) mm. Wing length 3.64–4.36 (4.17) mm. Total length/wing length 1.03–1.23 (1.14).

Coloration. Dark brown. Head, thorax, abdomen, and hypopygium dark brown. Antenna greyish. Legs brown to dark brown. Wings greyish.

Head. Eyes reniform, bare. Temporal setae including 10–19 preoculars, 14–23 verticals and 17–18 postorbitals. Clypeus with 12–21 setae. Antenna with 13 flagellomeres and well-developed plume; terminal flagellomere with 1 subapical seta, 48–56 μm long; pedicel with 3 setae, 68–108 μm long; AR 1.31–1.71 (1.53). Palpomere length (μm) (n = 6): 48–64, 112–136, 156–188, 164–200, 204–304. Palpomere 3 in distal part with sensilla capitata with diameter 20 μm. Head width/palpal length 0.90–1.27 (n = 6).

Thorax. Antepronotum with 5–11 (9) ventrolateral setae. Dorsocentrals 10–15 (13), prealars 7–17 (14). Scutellum with 23–36 setae (n=4).

Wing. Width 1.12–1.40 (1,24) mm. Costal extension 115–131 (118) μm long. Anal lobe outline rounded. Squama with 44–61 (54) setae. R and R 1 with 21–38 setae, R 4+5 with 3–15 setae. RM/MCu 2.5.

Legs. Spur of front tibia 80–92 µm long. Spurs of mid tibia 52–60 µm and 52–76 µm long. Spurs of hind tibia 60–68 µm and 88–104 µm long. Hind tibial comb with 21 setae. Length (μm) and proportions of leg segments are as in Table 1.

Hypopygium ( Figs 7–16 ). Tergite IX with 8–22 setae on one side; anal point narrow and long, slender distally but broadening basally, 136–184 µm long and 8–9 µm wide distally, with minute apical rounded peg ( Fig. 9 ). Laterosternite IX with 5–11 setae. Transverse sternapodeme (TSA) trapezoidal or rounded ca 280 µm long. Phallapodeme 156 µm long. Gonocoxite 276–344 µm long; large inferior volsellae covered with long setae ( Figs 7 , 12–16 ). Gonostylus 148–192 µm long, slightly curved when pressed against the gonocoxite, with a slightly convex outer edge and an almost straight inner edge; in some males, a slight protrusion is noticeable along the inner edge in the basal half ( Figs 8, 10 ). When bent back, the gonostylus is expanded basally ( Figs 11 , 16 ), its surface with short setae; apex with subterminal peg and short macroseta, ca 8 µm long. HR 1.5–2.1.

Pupa (n=4) brownish, exuviae brownish yellow to yellow. Total length 5.2–6.4 mm.

Cephalothorax. Frontal tubercles reduced, frontal apotome with 2 setae 280–308 μm long. Thorax scaly in anterior part and wrinkled in posterior. Thoracic horn filiform, 388–528 µm long, brown at base, yellowish distally, approximately same width (16–20 µm) up to the middle, then gradually narrows and at top with some small teeth. Two dark brown precorneal setae anterior to thoracic horn: Pc 1 330–355 μm, Pc 2 236–285 µm long ( Fig. 17 ). Antepronotum with 2 median setae 132–164 µm long and 1 lateral antepronotal 64–88 µm long. Mesonotum with 2 dorsocentrals: Dc 1 strong, 300–336 μm long, Dc 2 hair-like, 28–32 μm long.

Abdomen. Tergite I without shagreen or teeth. Tergites II–VII with shagreen in anterior third or half, tergite VIII almost covered with shagreen. Sternites I–II without shagreen, sternites III–VIII with sparse shagreen and IX without shagreen. Tergite I and sternites I–II without posterior transverse row of spines. Tergites II—VIII with posterior transverse row spines, number of these spines on these tergites: 7–12, 7–12, 8–11, 7–9, 6–8, 7–10, 5–9 ( Figs 18–19 ). Number of posterior transverse row spines of sternites III–VIII: 7–9, 9–11, 8–10, 8–13, 8–14, 8–15 ( Fig. 20 ). The total number of spines of the anal rows of tergites 55–57 and sternites 69–73. Segment I with 2 pairs of lateral setae, 48–96 μm long; segments III–VII with 3 pairs of strong lateral setae, 152–208 μm long (L 1 –L 3) and 1 pair of hair-like setae, 24–100 μm long (L 4). Segment VIII with 3 pairs of lateral setae 80–216 μm long. Segments II –VIII with spinelike process on posterolateral corners. Anal lobe with 3 yellow anal macrosetae, 292–312 μm long, slightly curved in distal part and pointed. Male genital sac not extended or slightly extended beyond anal lobe ( Fig. 21 ).

Fourth instar larva (n = 4). Total length 6.5–8.5 mm. Head capsule uniformly dark brown to black., 656–672 µm long and 380–492 µm wide. S I and S II short and simple, S III bifurcate, hair-like. Labral lamellae consisting of 5 lobes. Premandible broad, apically with 6–7 teeth ( Fig. 24 ). Antenna with 5 segments; Lauterborn organs small; style reaches base of fourth segment; longest branch of antennal blade reaches the apex of the fourth segment; large ring organ located in basal quarter of first segment ( Fig. 22 ); AR 1.55–1.80, (1.68). Mandible dark brown to black, with apical tooth and 4 inner teeth; apical tooth slightly longer than the first inner tooth; seta subdentalis minute; seta interna with 24–26 simple branches ( Fig. 25 ). Mentum with 1 median and 9–10 pairs of lateral teeth; median tooth twice as wide as the first lateral tooth and same height as it; ventromental plate small ( Fig. 23 ). Procercus dark brown, in the form of incompletely sclerotized ring, bearing 4 dark brown strong anal setae, 268–308 µm long and 1 hair-like lateral seta which is on the body, 56–60 µm long. Posterior parapod is 2 times as long as the last body segment. Dorsal and ventral pairs of anal tubules 160–212 µm long, dorsal pair is slightly thicker.

Remarks. Unfortunately, a detailed comparative morphological analysis of the adult males of known populations of D. gregsoni cannot be carried out due to insufficient data for individuals from Canada and Norway, but nevertheless, it can be stated that the males are similar in some basic features ( Table 2) and in the structure of the hypopygium. However, it should be noted that there is a difference in the shape of the gonostylus of males shown in the original description ( Edwards 1933) from Akpatok Island ( Figs 2–3 ), New Brunswick ( Hansen & Cook 1976) ( Figs 5–6 ), Norway (Sierra- Tosio 1971) ( Fig. 4 ), and the Far East ( Figs 7–16 ). This may be due to the position of the gonostylus relative to the gonocoxite, as well as geographic variability, but the protrusion along the outer edge in the basal third of the gonostylus ( Figs 8, 10 ) is present only in males from the Far East. In our opinion, a revision of D. gregsoni adult males from North America and other areas is necessary in the future to determine the degree of variability in the form of the gonostylus.

Biology and ecology. In North America, adults were caught in the first half of April in New Brunswick and in early September on Akpatok Island, Nunavut ( Hansen & Cook 1976). In Europe, the species was collected in Norway at an altitude of 1837 m a.s.l. on August 11 (Serra-Tosio 1971). In the Far East, the species is bivoltine. In Kamchatka, the emergence of adults occurs from the first half of June to mid-July and in the first half of October. On the Ola River in the vicinity of Magadan City D. gregsoni adults were caught in late April–early May and late November. The earliest collection of males in the vicinity of Magadan City on the Dukcha River was on April 22 on the snow. In the Amur River basin, adults were collected in late May and July, on Sakhalin, in late July at an altitude of 743 m a.s.l.

Larvae and pupae live in foothill and mountain rivers on cobble and gravel substrates with interstitial sand ( Figs 26–29 ).

Distribution. According to our data D. gregsoni currently known from Canada (Akpatok Island in the Hudson Strait, Nunavut, New Brunswick, Newfoundland, Labrador, Yukon Territory), USA (Alaska, California), Norway, Japan (Hokkaido Island) and the Russian Far East—in the vicinity of Magadan, from the Kamchatka Peninsula, Sakhalin Island, the Amur River basin and the northeast of Khabarovsk Territory. Ashe & O’Connor (2009) also pointed out to the occurrence of this species in Sweden, Novaya Zemlya and China. We believe that this information should be clarified.

Figures

FIGURE 2–11. Adult male hypopygium structures of Diamesa gregsoni Edwards. 2, gonocoxite and gonostylus; 3–4, 6–7, hypopygium in dorsal view, with tergite IX; 5, hypopygium in dorsal view, without tergite IX; 8, 10–11, gonostylus in varies positions; 9, apex of anal point. Figs 2–3, holotype, (after Edwards 1933); Fig. 4, from Norway (after Serra-Tosio 1971); Figs 5–6, from North America (after Hansen & Cook 1976); Fig. 7, from Kamchatka (after Makarchenko 1985). Scale bars—Figs 7–8, 10–11—50 µm; Fig. 9—20 µm.

FIGURE 12–15. Adult male hypopygium of Diamesa gregsoni Edwards in dorsal view from Ola River (Magadan Region of Russia) (12), Hokkaido (Japan) (13), Sakhalin Island (Russia) (14) and Amur River basin (Russia) (15). Scale bar—50 µm.

FIGURE 16–21. Adult male (16) and pupa (17–21) of Diamesa gregsoni Edwards. 16, part of hypopygiuim without tergite IX; 17, thoracic horn and precorneals; 18, tergite IV; 19, tergite VIII; 20, posterior transverse row spines of sternite V; 21, anal segment. Scale bars—Figs 16–17—50 µm; Figs 18–21—200 µm.

FIGURE 22–25. Larva of fourth instar of Diamesa gregsoni Edwards. 22, antenna; 23, mentum; 24, distal part of premandible; 25, mandible. Scale bars are 20 µm. Figs 22, 24–25 redrawn from Makarchenko (1985). Scale bars—20 µm.

FIGURE 26–29. Localities of Diamesa gregsoni Edwards. 26–27, Sakhalin Island, Chamginsky Pass, Khrebtovyi Stream, alt. 743 m a.s.l. (Photos by E.A. Makarchenko); 28, Kamchatka, Paratunka River (photo by A.A. Semenchenko); 29, Amur River basin, Anyuisky National Park, Pikhtsa River (tributary of Gassi Lake) (photo by N.M. Yavorskaya).