Metriocnemus griseovittatus 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 : 911-914

Metriocnemus griseovittatus Edwards

Metriocnemus griseovittatus Edwards 1931: 271 ; Spies and Reiss 1996: 78 (unplaced valid species in Orthocladiinae ); Ashe and O̍Connor 2012: 657 (generically unplaced valid Orthocladiinae ).

Material examined

2 J syntypes, ′ Argentina: Terr . Rio Negro , Bariloche, 25/ 28 .x .1926, F . and M . Edwards leg. ( NHM)̍. One of the syntypes is pinned with the hypopygium mounted in Canada balsam; the other is slide mounted .

Male imago (n = 1, except the hypopygium measures with n = 2)

Total length 4.38 mm. Wing length 2.5 mm. Total length/wing length 1.75. Wing length/length of profemur not measurable. Colouration uniformly dark brown with legs light brown.

Head. Antennae with 13 flagellomeres, ultimate flagellomere 701. AR 1.46. Temporal setae 19. Clypeus with 9 setae. Tentorium 198 long, 44 wide. Stipes not measurable. Lengths of palpomeres: 44; 85; 259; 173; 235.

Thorax. Antepronotum with 12 lateral setae. Dorsocentrals 44; acrostichals 18; prealars 18; supraalars 2. Scutellum with 28. Preepisternals absent.

Wing. VR 1.28. Brachiolum with 6 setae; R 52; R 1 44; RM 2; M 8; M 1+2 65–78 (2); Cu 55. C extension, Squama, Sc, R 4+5, M 1+2, M 3+4, Cu 1, Pcu, and An not measurable.

Legs. Spur of front tibia 93 long; spurs of middle tibia: 47–51 and 40–65; of hind tibia: 47 and 112. Width at apex of front tibia 60; of middle tibia 56; of hind tibia 84. Comb absent. 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 in Table 3 .

Hypopygium ( Figure 2 (b)). With anal point. Setae on tergum IX 23–32, laterosternite IX with 9 setae. Phallapodeme 68–97 long; transverse sternapodeme 82–88 long. Virga absent. Gonocoxite 303–323 long; inferior volsella strongly projecting, ending at 0.78– 0.8. Gonostylus 132–135 long; crista dorsalis very low; megaseta 15–18 long. HR 2.30–2.39; HV 3.32 (1).

Diagnosis

The following combination of characters clearly differentiates M. griseovittatus from the other species of the genus: anal point tapering to sharply pointed, inferior volsella well developed lobe-like, crista dorsalis very low, LR 2 0.40–0.45, LR 3 0.57–0.61, M vein without setae, scutellar setae 20–32, prealar setae 5–21, acrostichal setae 9–21, dorsocentral setae 34–55, antepronotal setae 12–16, and temporal setae 19–29.

Remarks

Edwards mentioned that the anal point is lacking in Metriocnemus griseovittatus . The specimen mounted in Canada balsam showed an anal point ( Figures 2 (c), 4). The species M. griseovittatus closely resembles M. fuscipes (Meigen) , only differing in the quantitative characters listed in the diagnosis. It is possible that M. griseovittatus could be a junior synonym of M. fuscipes but since the immature stages of the former are not known, this species is kept as such. The type locality of this species is in the Subantarctic biogeographic province ( Cabrera and Willink 1980) comprising valleys and mountains with temperate humid climate. The dominant vegetation is Nothofagus forest with small areas of evergreen forest, but there are also prairies and extensive peat bogs occur.

Figures

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.