Metriocnemus fasciventris Edwards, 1931

Donato, Mariano, Zanotto Arpellino, Juan Pablo & Siri, Augusto, 2023, Revision of the species described in Metriocnemus van der Wulp (Diptera: Chironomidae) by Edwards (1931), with the description of two new species, Journal of Natural History (J. Nat. Hist.) 57 (13 - 16), pp. 904-923 : 908-911

Metriocnemus fasciventris Edwards

Metriocnemus fasciventris Edwards, 1931: 319 ; Spies and Reiss 1996: 78 (unplaced valid species in Orthocladiinae ); Ashe and O̍Connor 2012: 656 (generically unplaced valid Orthocladiinae ).

Material examined

3 J paratypes, ′ Argentina: Buenos Aires, San Isidro , 21 .x .1926, F . and M . Edwards leg . ( NHM)̍; 1 J with larval and pupal exuviae, ′ Argentina, Buenos Aires, City Bell, A ° Carnaval , −34.870588 − 58.089776, 8 m asl ., 7.viii.2018, Hand net, J .P . Zanotto Arpellino leg ( ILPLA)̍; 1 J pharate adult, same collection data as the preceding specimen, except ̍ 29 .v .2018̍ ( ILPLA) (not measured); 1 pupal exuvia, same collection data as the preceding specimen, except ′ 7 .viii .2018̍ ( ILPLA) (not measured).

Male imago (n = 4, except when otherwise stated, in parentheses).

Total length 3.24–3.88 mm (3). Wing length 1.7–2.24 mm. Total length/wing length 1.73–1.91 (3). Wing length/length of profemur 1.99–2.20. Colouration uniformly dark brown with legs light brown.

Head. Antennae with 13 flagellomeres, ultimate flagellomere 505–561. Antennal ratio (AR) 1.07–1.45. Temporal setae 34–46, divided in 21–35 inner verticals, 7–11 outer verticals and 3–7 postorbitals. Clypeus with 26–40 setae. Tentorium 156–228 long and 36–47 wide. Stipes 160–223 long, 74–93 wide (3). Lengths of palpomeres: 30–65; 42–70; 200–274, (3); 154–200 (3); 230–260 (3).

Thorax. Antepronotum with 9–12 lateral setae. Dorsocentrals 71–97; acrostichals 35–59; prealars 40–48, divided in 19–22 anterior prealars and 21–26 posterior prealars; supraalars 3–4. Scutellum with 28–43 setae. Preepisternals 11–16.

Wing ( Figure 1 (a)). VR 1.26–1.37. C extension 116–174. Brachiolum with 7–10 setae; Sc with 59–73 (3); R 55–71; R 1 57–72; R 4+5 75–128; RM 4–5; M 16–35;M 1+2 65–78 (2); M 3+4 52–59 (3); Cu 58–59 (2); Cu 1 30–36 (3); Pcu 100 (1); An 70 (1) setae. Squama with 15–30 setae (3).

Legs. Spur of front tibia 84–116 long; spurs of middle tibia: 36–60 and 40–65; of hind tibia: 36–47 (2) and 80–117. Width at apex of front tibia 42–60; of middle tibia 44–60; of hind tibia 54–82. Comb with 9–10 setae. Tarsomere 1 of middle and hind leg each with 2 pseudospurs; tarsomere 2 of middle and hind leg with 1 pseudospur. Lengths (in μm) and proportions of legs given in Table 2 .

Hypopygium ( Figure 2 (a)). With anal point. Setae on tergum IX 28–34, laterosternite IX with 6–9 setae. Phallapodeme 68–97 long; transverse sternapodeme 90–138 long. Virga absent. Gonocoxite 224–294 long; inferior volsella strongly projecting, ending at 0.62–0.7. Gonostylus 116–150 long; crista dorsalis very low; megaseta 8–12 long. HR 1.79–1.96; HV 2.43–2.79 (3).

Pupa (n = 1)

Exuviae light brown. Cephalothorax partially broken. Median antepronotals 2. Distance between Dc 1 and Dc 2 56; between Dc 2 and Dc 3 28; between Dc 3 and Dc 4 22.

Abdomen. Tergite I–II bare; T II–VIII with a row of teeth; T III–VIII with an anterior band of strong pointed spinules, TVI–VIII anteriomedian patch of weak shagreen ( Figure 3 (a)). Sternites I–II bare; S III– VI with posterior band of fine shagreen ( Figure 3 (b)). Anal lobe 300–320 long, without macrosetae. Genital sac 370–400 long.

Larva (n = 1)

Total length about 2.5 mm (exuviae only). Head capsule length 0.32 mm. Colouration light brown.

Head. Length of antennal segments: 40; 10; 8; 4; 2. AR 1.46. Basal antennal segment 20 wide; distance from base to ring organ 8; to basal mark of seta 14; blade 30 long; accessory blade not measurable. Premandible 42 long; brush apparently absent. Mandible 118 long, apparently with 5 branches in seta interna. Mentum ( Figure 4 ) with central teeth lower than first pair of lateral teeth. Postmentum 160 long.

Abdomen. Procercus 60 high; 48 wide. Posterior parapods 180 long. Anal tubules 130 long, 30 wide at base.

Diagnosis

The combination of characters anal point tapering to sharply pointed, virga absent, welldeveloped lobe-like inferior volsella, crista dorsalis very low, AR 0.92–1.67, number of dorsocentral setae more than 78, number of setae on squama 19–33, LR 1 0.68–0.74, HR 1.87–2.06, and HV 2.31–2.72 differentiates M. fasciventris from the other the species of the genus.

Remarks

This species occurs in the Pampean biogeographic province ( Cabrera and Willink 1980) that occupies the plains of eastern Argentina, Uruguay, and southern Brazil. Its climate is warm temperate with rains all year round. The predominant vegetation is the pseudosteppe of grasses but there are also edaphic communities, halophytic steppes, marginal forests on the banks of the rivers and xerophytic forests in shell soils.

Figures

Figure 1. Metriocnemus wings. (A) M. fasciventris Edwards; (B) M. cavipenis sp. nov.; (C) M. tucumanus sp. nov. Scale bars: 100 µm.

Figure 2. Metriocnemus male genitalia. On the left, dorsal aspect; on the right, hypopygium with anal point and tergite IX removed. (A) M. fasciventris Edwards; (B) M. griseovittatus Edwards; (C) M. cavipenis sp. nov.; (D) M. tucumanus sp. nov. Scale bars: 100 µm.

Figure 3. Metriocnemus fasciventris Edwards pupae. (A) Tergites; (B) sternites III/VI. Scale bar: 100 µm.

Figure 4. Metriocnemus fasciventris Edwards larvae. Mentum. Scale bar: 10 µm.