Metriocnemus tucumanus Donato, 2023

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 : 916-918

Metriocnemus tucumanus Donato sp. nov.

Male imago (n = 1)

Material examined

1 J holotype, ′ Argentina: Tucumán, RP 307, La Heladera, 27° 1̍ 55″S, 65° 39̍ 24″W, 1215 m asl ., 9.xi.2014, Hand net, M . Donato leg . ( MLP)̍.

Total length 3.58 mm. Wing length 1.88 mm. Total length/wing length 1.90. Wing length/length of profemur 2.21. Colouration uniformly dark brown with legs light brown.

Head. Antennae with 13 flagellomeres, ultimate flagellomere 513. AR 1.32. Temporal setae 27. Clypeus with 42 setae. Tentorium 162 long, 44 wide. Stipes not measurable. Lengths of palpomeres: 48; 52; 220; 160; 236.

Thorax. Antepronotum with 9 lateral setae. Dorsocentrals 66; acrostichals not measurable; prealars 21; supraalars 1. Scutellum with 29 setae. Preepisternals 12.

Wing ( Figure 1 (c)). VR 1.25. Brachiolum with 8 setae; Sc 53; R 76; R 1 48; R 4+5 125; RM 4; M 25. M 1+2; M 3+4; Cu; Cu 1; Pcu and An not measurable. C extension 340, Squama with 24 setae.

Legs. Spur of front tibia 74 long; spurs of middle tibia: 40 and 42; of hind tibia: 84, the other not measurable. Width at apex of front tibia 48; of middle tibia 50; of hind tibia 60. Comb with 8 setae. Tarsomere 1 of middle and hind leg each with 2 pseudospurs; tarsomere 2 and 3 of middle and hind leg with 1 pseudospur. Lengths (in μm) and proportions of legs in Table 5 .

Hypopygium ( Figure 2 (d)). Anal point present. Setae on tergum IX 31, laterosternite IX with 6 setae. Phallapodeme 62 long; transverse sternapodeme 90 long, with strong anterolateral processes. Virga absent. Gonocoxite 208 long; inferior volsella strongly projecting, ending at 0.59. Gonostylus 116 long; crista dorsalis very low; megaseta 8 long. HR 1.79; HV 3.09.

Etymology

Named after the political province of Tucumán ( Argentina), where the species was collected.

Diagnosis

The male imago is distinguishable from the other species of the genus by the following combination of characters: anal point tapering to blunt apex, virga absent, inferior volsella well developed lobe-like, crista dorsalis rounded, and transverse sternapodeme with strong anterolateral processes.

Remarks

The species M. tucumanus was collected in the Yungas biogeographic province ( Cabrera and Willink 1980), extended along the eastern Andes hillsides in a narrow strip from Venezuela to north-western Argentina. The biomes range from moist lowland forest to evergreen montane forest and cloud forests. The climate is cool and very humid, by reason of the abundant precipitation and especially because of the almost permanent cloud cover over the mountains. The province extends altitudinally between 500 and 2500–3500 m above sea level, varying with latitude.

Key to male imagines of Metriocnemus van der Wulp from the Neotropics

1. Anal point absent ................................................................................................................................ 2

- Anal point present .............................................................................................................................. 5

2. Penis cavity strongly sclerotised and developed ....... Argentina, M. cavipenis sp. nov.

- Penis cavity not as above ................................................................................................................. 3

3. Thorax with no more than 33 dorsocentral setae. ..................................................................... ................................................................................................. Argentina, M. puna Donato and Siri

- Thorax with more than 33 dorsocentral setae ........................................................................ 4

4. Thorax with 56–77 dorsocentral setae ....... Guatemala, M. virgatus Sublette and Sasa

- Thorax with more than 78 dorsocentral setae ............................................................................... ....................................................................... Argentina, M. eryngiotelmatus Donato and Paggi

5. Inferior volsella well developed, lobe-like ................................................................................. 6

- Inferior volsella well developed with apical swelling .................................................................. ................................................................................................ Argentina, M. griseovittatus Edwards

6. AR 0.16–0.91 .......................................................................................................................................... 7

- AR 0.92–1.67 .......................................................................................................................................... 8

7. Third palpomere with apical spiniform seta, 12 flagellomeres ............................................... ......................................................................................... Guatemala, M. lautus Sublette and Sasa

- Third palpomere without spiniform seta, 13 flagellomeres ...................................................... ..................................................................................... Guatemala, M. costatus Sublette and Sasa

8. Transverse sternapodeme with strong anterolateral processes, prealar setae 5–21, setae on R vein 72–98 ........................... ........................... Argentina, M. tucumanus sp. nov.

- Transverse sternapodeme without strong anterolateral processes, prealar setae 38– 53, setae on R vein 45–71 ....................... ....................... Argentina, M. fasciventris Edwards

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.