Stenochironomus bare, Dantas, Galileu P. S., Hamada, Neusa & Mendes, Humberto F., 2016

Dantas, Galileu P. S., Hamada, Neusa & Mendes, Humberto F., 2016, Contribution to the knowledge of Stenochironomus Kieffer (Diptera, Chironomidae) from Brazil: seven new species and description of females and immatures of some previously known species, Zootaxa 4117 (1), pp. 1-47 : 10-12

Stenochironomus bare new species

( Figs. 6–8 )

Type material. Holotype male with pupal and larval exuviae, BRAZIL: Amazonas State, Itacoatiara, Madeireira Mil, 02º 46’ 37.7’’ S, 58º 50’ 38.3’’ W, 13.v.09, in decayed leaves, G.P.S. Dantas ( INPA).

Diagnostic characters. Male: scutelum with 25 setae; anal point large at apex; inferior volsella with 4 setae, restricted to apex, apical setae stout; gonostylus with constant width along its length; HR<1. Pupa: tubercle on wing sheath; spines on apex of anal lobes and frontal apotome elongated.

Etymology. the species name is a reference to the “ Baré ” ethnic group, which occupied a large area in central Amazon. The name is to be treated as a noun in apposition.

Male (n = 1). Total length 4.61 mm. Wing length 1.95 mm. Total length/ wing length 2.36.

Coloration—Eyes markedly metallic green when alive or in alcohol. Thorax: light brown patch on anterior portion of lateral vitta; light-brown patch on central region of scutelum ( Fig. 6 B); a transversal light-brown band on the preepisternum. Wing: transparent membrane, with a medial light-brownish band. Legs: mid leg yellowish; hind femur yellowish, with a brownish band at base and at apex; hind tibia yellowish, with a basal brownish band, tarsus yellowish. Abdomen: brown pigmentation on posterior margin of T II–III and posterolateral margin of T VIII; hypopygium light brown, with bare areas near pre-apical constrictions.

Head ( Fig. 6 A). AR 2.05. Thirteenth flagellomerum 840 µm long. Temporal setae 10, extending to the posterior margin. Clypeus with 21 setae. Tentorium, stipes and cibarial pump as in Figure 6 A. Tentorium 167 µm long; 40 µm wide at sieve pore; 28 µm wide at posterior tentorial pit. Stipes 151 µm long; 7 µm wide. Palpomere length (1–3 in µm): 44; 52; 180.

Thorax ( Fig. 6 B). Acrostichals 10; dorsocentrals 11, in a single row; prealars 7, in two rows. Scutellum with 25 setae in two rows. Anterior edge of scutum angled in lateral aspect.

Wing ( Fig. 6 C). VR 1.10. Brachiolum with 3 setae, with about 20 sensilla campaniformia. R with 32 setae; R1 with 35 setae; R4+5 with 52 setae; M with 1 setae; RM with 1 setae; remaining veins bare . Squama with 8 setae. Legs. Spurs of middle tibia 41 µm and 50 µm long; spurs of hind tibia 46 µm and 49 µm long. Apex of mid tibia 60 µm wide, of hind tibia 64 µm wide. Lengths (in µm) and proportions of legs as in Table 3 .

Hypopygium ( Figs. 7 A, 7B). Anal point large at base; 86 µm long; 19 µm wide at base; 17 µm wide at half; 29 µm wide at apex. Tergite IX with 35 setae, caudal apex edge-shaped, with several setae posterior to the pre-apical constriction. Laterosternite IX with 4 setae. Phallapodeme 111 µm long; transverse sternapodeme 47 µm long. Gonocoxite 170 µm long; inferior volsella 188 µm long, with 4 setae, restricted to apex, apical setae stout; superior volsella 62 µm long, with 6 setae. Gonostylus 185 µm long, with constant width along its length. HR 0.92. HV 2.49.

Pupa (n = 1). Total length 5.46 mm. General coloration light brown.

Cephalothorax ( Figs. 8 A, 8B). Frontal apotome markedly elongated ( Fig. 8 A); frontal warts absent. Precorneal setae 127 µm long. Dorsocentrals (Dc) 98 µm long. Distance between Dc1 and Dc2 6 µm; between Dc2 and Dc3 122 µm; between Dc3 and Dc4 4 µm. Median suture smooth. A ventral tubercle close to wing sheath base; a laterodorsal tubercle, anterior to Dc1 ( Fig. 8 B).

Abdomen ( Figs. 8 C, 8D). T I bare ; T II–III with large field of shagreen, slightly thicker near posterior margin, with a somewhat circular bare area near anterior margin; T IV with large field of shagreen, thicker near posterior margin, with a somewhat elliptical bare area near anterior margin, paratergites with posterior fine shagreen; T V with two fields of shagreen separated by 117 µm, one anterior larger field of thinner shagreen with a central bare area larger anteriorly, and one posterior smaller field of thicker shagreen; T VI with two fields of shagreen separated by 64 µm, one anterior somewhat triangular field of thinner shagreen, and a posterior field of thicker shagreen; T VII–VIII with shagreen restricted to a small area near anterolateral margin; anal segment with anterior pair of shagreen patches. T II with posterior row of hooklets not extending to lateral margin of tergite, divided medially into two groups by 38 µm, each row 100 µm long; pedes spurii B absent. Abdominal setation: S I without L setae; S II–IV with 3 L setae; S V–VII with 4 LS setae; S VIII with 5 LS setae. Spur on S VIII ( Fig. 8 E) with teeth yellowish brown, with one extremely elongate lateral tooth 130 µm long, an elongate penultimate tooth 56 µm long, and four smaller medial teeth; from a dorsal view, teeth arranged in a slightly curved row ( Fig. 8 D). Genital sac 257 µm long, overreaching the posterior margin of the anal lobe by 15 µm; anal lobe with fringe of about 42 filaments, apex rounded, with spicules ( Fig. 8 F).

Female and larva unknown.

Systematic remarks. Borkent (1984) described a pupal morphotype (“pupal form one”) that was associated with the genitalia of a male, probably pharate, indistinguishable from S. bacrionis Borkent. According to the author the two species could be differentiated by pupal features, which in the morphotype have spicules on the posterior region of the anal lobes, missing in the pupae of S. bacrionis . The pupa of S. bare sp. n. has such spicules on the anal lobes, but the male can be distinguished from S. bacrionis by the size of the superior volsella, that in the first species does not exceed the apex of the gonocoxite. The new species is also similar to S. triannulatus Borkent by the pigmentation of the thorax and wings and by the general morphology of the hypopygium. However, S. bare sp. nov. has the preapical constriction of T IX more pronounced, gonostylus with constant width along its length, hind tibia with one brown band, abdominal brown pigmentation on posterior margin of T II–III and posterolateral margin of T VIII, whereas S. triannulatus has the preapical constriction of T IX less pronounced, gonostylus with a preapical swelling, hind tibia with two brown bands, abdominal brown pigmentation on very lateral and posterior margins of T II–IV and posterior margin of T VI.

Notes on biology of the species. The stream where S. bare sp. nov. was collected is a small typical blackwater stream of the Amazon lowlands forest, with an average width of 1.5 m (range: 0.70–2.20), average depth of 0.10 m (range: 0.033–0.240) and average flow of 0.02 m 3/s (range: 0.004–0.148). These water courses are characterized by acidic black water (average = 4.50, range: 2.60–6.00), low conductivity (average = 7.60 µS/cm, range: 6.80–9.95), high concentration of dissolved oxygen (average = 6.50 mg /L, range: 5.12–7.10) and low temperature variation (average = 24.6 C, range: 23.2–25.5). The opening of the forest canopy was small (average = 0.07%, range: 0.02–0.19) and the dominant substrate types in the stream beds were sand (average = 31%, range: 3– 61), coarse litter (average = 28%, range: 6–50) and fine litter (average = 13%, range: 0–41).

Figures

FIGURE 6. Stenochironomus bare sp. nov., adult male. A, head. B, thorax. C, wing.

FIGURE 7. Stenochironomus bare sp. nov., adult male. A, hypopygium in dorsal view. B, hypopygium with tergite IX removed, left dorsal view, right ventral view.

FIGURE 8. Stenochironomus bare sp. nov., pupae. A, frontal apotome. B, anterior part of thorax, in lateral view. C, tergites I – IV. D, tergites V – IX. E, spur on S VIII. F, apex of anal lobes.

Tables

TABLE 3. Lengths (in µm) and proportions of leg segments of Stenochironomus bare sp. nov., adult male (n = 1).

	fe	ti	ta1	ta2	ta3	ta4	ta5	LR	BV	SV	BR
P1
P2	1090	943	666	359	233	166	76	0.71	3.24	3.05	3.1
P3	1286	1174	873	476	354	225	89	0.74	2.91	2.82	5.6