Orthocladius (Mesorthocladius) nimidens, Saether, Ole A., 2005

Saether, Ole A., 2005, A new subgenus and new species of Orthocladius van der Wulp, with a phylogenetic evaluation of the validity of the subgenera of the genus (Diptera: Chironomidae), Zootaxa 974, pp. 1-56 : 36-42

Orthocladius (Mesorthocladius) nimidens sp. n.

O. sp. “Jacobsen” ( Epler 2001: 7.99, 7.109)

( Figs. 18–22 , 25–27 , 33, 34 , 37, 38 , 41–46 )

Type material

Holotype ɗ reared from larva, USA: Ohio, Franklin Co., Sharon Woods Park, woodland trickle, 28 iii emerged 2 iv 1987, M. J. Bolton ( ZMBN Type No.407). Paratypes: 3 mature ɗ pupae reared from larva, 3 mature Ψ pupae reared from larva, 3 pupal exuviae, 3 larvae, as holotype except 22–26 iv 1987, M. J. Bolton ( ZMBN)

Diagnostic characters

The male imago differs from all other species of the genus by means of the triangular anal point. The apical wart of the seminal capsule, the evenly wide spermathecal ducts with several loops, and the lack of an anterior projection of the dorsomesal lobe of gonapophysis VIII all are unique within the genus. The combination of prominent frontal warts, granulose pedes spurii B on segment II, thoracic horn covered with spinules, and minute lateral threads but no apical spines on the anal lobe separates the pupa from other members of the genus. The mentum with 15–17 teeth combined with a bifid premandible, very broad median tooth of the mentum, and presence of seta interna of the mandible separate the larva from other members of the genus.

Male imago (n = 3–4 except when otherwise stated)

Total length 3.35–4.30, 3.95 mm. Wing length 1.72–1.96 mm (2). Total length/wing length 1.95–2.07 (2). Wing length/length of profemur 2.44–2.49 (2). Coloration brown with dark brown vittae.

Head ( Fig. 41 ). AR 1.76–1.92, 1.84. Ultimate flagellomere 567–652, 614 µm long. Temporal setae 11–14, including 4–5 inner verticals, 4–5 outer verticals, and 3–4 postorbitals. Clypeus with 5–8, 6 setae . Cibarial pump, tentorium and stipes as in Fig. 41 . Tentorium 195–206 µm (2) long, 49 (2) µm wide. Stipes 146–158 µm (2) long, 56–60 µm (2) wide. Palpomere lengths (in µm): 34–47, 53–64, 75–101, 68–86, 113–135 (2).

Thorax ( Fig. 42 ). Antepronotum with 6–8, 7 setae . Dorsocentrals 15–18, 16, uni­biserial; acrostichals 6–11, 8; prealars 7–8, 8; 1 supraalar. Scutellum with 14–17, 16 setae ; unibiserial.

Wing ( Fig. 43 ). Anal lobe moderately to strongly produced. VR 1.03–1.06 (2). Costal extension 38–49 µm (2) long. Brachiolum with 1 seta, R with 7–9, 8 setae ; other veins bare. Squama with 17–24, 19 setae .

Legs (n = 2). Spur of front tibia 71–94 µm long, spurs of middle tibia 34–45 and 24–41 µm long, of hind tibia 68–83 and 26–38 µm long. Width at apex of front and middle tibia each 45–56 µm, of hind tibia 56–68 µm. Pseudospurs present on ta1 of mid and hind leg, ta2 of mid leg and occasionally ta2 of hind leg, 26–32 µm long. Sensilla chaetica absent. Lengths (in µm) and proportions of legs:

Hypopygium ( Figs. 44–46 ). Anal point 86–120, 109 µm long, triangular with pointed apex. Tergite IX including anal point with 16–20, 19 setae ; laterosternite IX with 7–10, 9 setae . Phallapodeme 124–135, 130 µm long; transverse sternapodeme 94–131 µm long, oral projections moderately developed. Gonocoxite 266–311, 288 µm long; inferior volsella with ventral part reduced, not extended beyond dorsal part. Gonostylus 113–131, 122 µm long; crista dorsalis low or absent; megaseta 11–15 µm long. Virga absent. HR 2.34–2.37, 2.36; HV 2.97–3.50, 3.24.

Female imago (n = 3)

Total length 3.83–4.19 mm. Wing length 1.95–2.28 mm. Total length/wing length 1.80–2.05. Wing length/length of profemur 2.61–2.84. Coloration not as dark as in male with more distinct markings.

Head. AR 0.46–0.49. Flagellomere lengths (in µm): 90–101, 56, 49–56, 60–68, 124– 135. Coronal suture 113–128 m long. Temporal setae 14–16, including 4–6 inner verticals, 6–7 outer verticals, and 4–5 postorbitals. Clypeus with 8–12 setae . Tentorium 154– 191 µm long, 38–49 µm wide. Palpomere lengths (in µ m): 41–45, 53–64, 90–124, 79–94, 129–143.

Thorax. Dorsocentrals 14–19, acrostichals 6–17, prealars 7–10. Scutellum with 18–21 partly biserial setae .

Wing. Anal lobe very slightly produced. VR 1.06–1.11. Costal extension 56–60 µm long. Brachiolum with 1–3 setae , R with 79–18, R1 with 6–11. R4+5 with 11–18 setae . Squama with 17–24, 19 setae .

Legs. Spur of front tibia 41–45 µm long, spurs of middle tibia 30–38 and 28–34 µm long, of hind tibia 68–85 and 26–38 µm long. Width at apex of front tibia 45–56 µm, of middle tibia 53–62 µm, of hind tibia 60–71 µm. Pseudospurs present on ta1 of mid and hind leg, ta2 of mid leg and occasionally ta2 of hind leg, 30–34 µm long. Sensilla chaetica absent. Lengths (in µm) and proportions of legs:

Abdomen. Tergite VIII with 30–50 setae , sternite VIII with 35–39 setae .Genitalia ( Figs. 18–22 ). Tergite IX strongly divided with margins well delimited, with 33–40 setae . Gonocoxite with 14–19 setae . Cercus 169–188 µm long. Seminal capsule pear­shaped with more or less well developed apical wart, 105–130 µm long including about 45 µm long tapering neck, 64–68 µm wide, sclerotised in anterior 75–94 µm. Spermathecal ducts with several loops and apparently separate openings. Notum 98 µm long. Dorsomesal lobe of gonapophysis VIII without anterior projection. Labia with very fine microtrichiae medially, apodeme of apodeme lobe strong.

Pupa (n = 9–10) Total length 4.29–5.78, 4.89 mm. Exuviae pale brown with darker thorax and apex of anal lobe and blackish brown apophyses.

Cephalothorax. Frontal warts ( Fig. 27 ) relatively pronounced. Frontal setae 64–139, 103 µm long. Thoracic horn ( Fig. 26 ) 266–428, 363 µm long; 49–68, 56 µm wide; 5.46– 7.85, 6.54 times as long as wide; 0.95–1.23, 1.11 times as long as anal macrosetae. Precorneal setae respectively 68–113, 96 µm; 86–169, 133 µm; and 56–98, 84 µm long. Anterior dorsocentral (Dc1) 71–120, 95 µm long; Dc2, 53–105, 75 µm; Dc3 71–94, 69 µm; and Dc4 79–116, 94 µm long. Distances (in µm): Dc1–Dc 2 30–60, 46; Dc2–Dc 3 26–64, 49; Dc3–Dc4 34–71, 55.

Abdomen ( Fig. 25 ). Tergite I bare, tergite II with weak median and anterolateral group shagreen and stronger posterior shagreen; strong, extensive shagreen on tergites III–VI, posterior spinules on tergite III stronger than anterior ones, of about the same size on IV– VI, spinule bands confluent with anterior shagreen reaching about as far lateral as posterior shagreen; tergite VII with weak median shagreen, VIII and IX with anterior group shagreen. Sternite I bare; II with weak lateral shagreen, II–V with stronger lateral, VI with lateral, anterolateral and posteromedian shagreen, VII with fewer anterolateral and posteromedian spinules, VIII with anterolateral V–VII with lateral plus anterolateral, VIII and IX with anterolateral shagreen. Pedes spurii A on sternites IV–VII. Pedes spurii B well developed, granulose, on tergite II only. Caudal hooklets on tergite II 61 –160, 111; in 4–5 rows. Segments II–VI each with 3 L setae , VII with 4, and VIII with 4–5 L setae . Lengths of L1–L5 setae on segment VIII (in µm) as: 79–165, 123; 86–199, 138; 90–184, 132; 139– 240, 186; 105–120 (present in 2 of 10 specimens).

Anal lobe 338–401, 374 µm long; each lobe with 9–14, 12 fine lateral spines; no posterior spines. Anal macrosetae subequal in length; 281–375, 326 µm long; 0.79–0.94, 0.87 as long as anal lobe. Male genital sac reaching about to apex of anal lobe.

Fourth instar larva (n = 8–9 except when otherwise stated)

Total length about 4.8–8.1, 6.2 mm. Head capsule 0.48–0.53, 0.51 mm long. Postmentum 225–263, 240 µm long. Head capsule light brown.

Head. Antenna as in Fig. 31 . Length of antennal segments (in µm): 73–86, 79; 15–17, 16; 4–7, 6; 3–4, 4; 5–6, 6. AR 2.38–2.81, 2.62. Ring organ 13–19, 17 µm from base; basal setal mark 16–25, 20 µm from base; apical setal mark 20–35, 28 m from base. Basal antennal segment 20–25, 22 µm wide; blade 20–26, 23 µm (6) long; accessory blade10– 17, 14 µm (8) long. Lauterborn organs 5–7, 6 µm (7) long; style 5–9, 7 µm long. Labrum ( Fig. 32 ) with one branch of S I split into 2–6 weak branches, S II double on one side in one specimen, 12 chaetae and 5 spinulae. Chaetulae laterales smooth. Premandible bifid ( Fig. 32 ), 98–109, 105 µm (8) long; vestigial brush indicated. Pecten galearis apparently absent. Mandible ( Fig. 37 ) 176–210, 189 µm long; seta interna of 7–8 branches. Mentum ( Fig. 38 ) 161–180, 169 µm wide; with 15 or 17 teeth, median tooth 35–47, 40 µm wide; ventromental plate 10–16, 14 µm wide; about 4 very weak setae present underneath ventromental plates on cardo.

Abdomen. Claws of anterior parapods strongly serrated. Longest body setae 131–278, 186 µm long. Posterior parapods 225–323, 280 µm (5) long. Procercus 41–56, 48 µm high; 26–45, 39 µm wide. Anal setae 544–675, 618 µm long; supraanal seta 143–206, 167 µm (8) long, 0.24–0.31, 0.27 (8) as long as anal setae . Longer anal tubules 151–188, 162 µm (6) long, 75–113, 94 µm (6) wide at base; shorter anal tubules 105–143 µm (3) long, 56–68 µm (3) wide at base.

Comments

The female imago is unique within the genus, with the apical wart on the seminal capsule, spermathecal ducts with several loops but no widened portions, dorsomesal lobe without the anterior projection characteristic for the Cricotopus­Orthocladius group of genera, and no discernible rami. The genitalia are surprisingly similar to those of some Diamesa Waltl. Other apparent autapomorphies within the genus are the triangular anal point of the male imago and the rounded, instead of concave, posterior part of the larval ventromental plates. However, the pupa shares several synapomorphies with other members of the subgenus such as prominent frontal warts, granulose pedes spurii B, and lateral threads on the anal lobe.

Ecology and distribution

The species inhabits vernal woodland shallow pools and springs. This habitat is only present in the spring when the groundwater level is high enough to supply them, or possibly they are created where an impermeable clay lens is pooling snow­melt and spring rains. The species is known from Ohio, Indiana, and North Carolina.

Figures

FIGURES 13 – 22. Orthocladius (Mesorthocladius) spp., female imagines, genitalia, 13 – 17: O. (M.) lamellatus sp. n., 13: ventral view, 14: ventrolateral lobe, 15: dorsomesal lobe, 16: apodeme lobe, 17: dorsal view, 18 – 22: O. (M.) nimidens sp. n., 18: ventral view, 19: ventrolateral lobe, 20: dorsomesal lobe, 21: apodeme lobe, 22 dorsal view.

FIGURES 23 – 27. Orthocladius (Mesorthocladius) spp., pupae, 23: O. (M.) lamellatus sp. n., tergites, 24: thoracic horn, 25 – 27: O. (M.) nimidens sp. n., 25: tergites, 26: thoracic horn, 27: frontal apotome.

FIGURES 28 – 34. Orthocladius spp., larvae, 28: Orthocladius (Mesorthocladius) frigidus (Zetterstedt) labrum, epipharyngeal area and premandible, 29, 30: Orthocladius (Orthocladius) nitidoscutellatus Lundström, 29: antenna, 30: labrum, epipharyngeal area and premandible, 31, 32: Orthocladius (Mesorthocladius) lamellatus sp. n., 31: antenna, 32: labrum, epipharyngeal area and premandible, 33 – 34: Orthocladius (Mesorthocladius) nimidens sp. n., 31: antenna, 32: labrum, epipharyngeal area and premandible.

FIGURES 35 – 40. Orthocladius spp., larvae, 35, 36: Orthocladius (Mesorthocladius) lamellatus sp. n., 35: mandible, 36: mentum, 37 – 38: Orthocladius (Mesorthocladius) nimidens sp. n., 37: mandible, 38: mentum, 39 – 40: Orthocladius (Orthocladius) nitidoscutellatus Lundström, 39: mandible, 40: mentum

FIGURES 41 – 46. Orthocladius (Mesorthocladius) nimidens sp. n., male imago, 41: head, 42: thorax, 43: wing, 44: hypopygium, 45: inner margin of gonocoxite, 46: gonostylus, different view.