Plecia marginata Edwards, 1920

Fitzgerald, Scott J., 2021, New species of Neotropical Plecia Wiedemann (Diptera: Bibionidae) and delineation of the americana-, nigra-, and xyele- species-groups, Zootaxa 5005 (1), pp. 21-40 : 28-31

Plecia marginata Edwards, 1920

( Figs. 10–17 )

Type Material. Holotype female: “Museum Paris, Équateur, Tulcan, Dr. G. Rivet, 1901.” ( MNHN) . Paratypes: topotypic, 2 females (1 MNHN, 1 BMNH), (all examined in 1998) .

Additional material examined. COLOMBIA: “ Cauca, Paramo de Parace, Lake San Rafael , 3570 m, 29.I.59, J. F. G. Clarke,” 1 female ( USNM); “Valle Tenerife, paramo at 12,000’, R.E. Dietz, 15 Sept. 1970,” 1 male ( USNM) .

Discussion. Edwards (1920) described Plecia marginata from three female specimens collected on the northern border of Ecuador at high elevation (“ Équateur. Tulcan, alt.: 3200m ”). Since then, no additional specimens have been reported and Hardy’s 1945 revision of the New World Plecia simply provides an English translation of the original description and states that “the writer has not seen this species.”

Species concepts in the genus Plecia rely heavily on characters of the male terminalia and many females are unknown, unassociated with males, or undescribed, making most unassociated females unidentifiable. However, the female of P. marginata has several features that make it somewhat distinctive. Firstly, is its’ very large size; Edwards (1920) states that the female wing is 11–13 mm (the present author’s measurements of the wings of the types is 10.5–12.0 mm), making it one of the largest species of New World Plecia . Secondly, is the dull black mesonotum with a narrow but continuous orange border; this color combination is very unusual and Hardy (1945) notes that the species “should be easily recognized by the orange border on the mesonotum and the reddish pleurae and abdomen.” During a visit to MNHN and BMNH in 1998 I had the opportunity to study the holotype (redescribed below) and paratypes of P. marginata and confirm both its large size and unique color combination.

During routine determinations of unsorted material from USNM, two specimens (one male and one female) from two high elevation (páramo) sites in Colombia were discovered that fit the description of this species. The female ( Figs. 10–12 ), collected about 204 km northwest of the type locality, matches the original description and my notes on the type series very well except that the abdomen is brown rather than reddish-brown and the wings are longer; wing length of this female is 14.5 mm, which is very large for this genus (nearly the known upper limit for the New World species). The male specimen ( Fig. 13 ) (exact locality difficult to discern from label data) largely matches the female in structure and color except vein R 2 +3 shorter and more divergent from R 4 +5 and the dark central area of the mesonotum is more brownish-black in color and subtly divided into broad stripes. The male is also smaller (wing 11.0 mm) than the Colombian female but falls within the wing length range of the type series and, in any case, males are usually smaller than females. Additionally, the male terminalia do not match any other known species suggesting it is either a new species or belongs to a species (e.g., P. marginata ) for which the male is unknown .

Based on the original description, as well as my notes from study of the type series, the female from Colombia appears to be conspecific with P. marginata . Whether the male and female specimens from Colombia are conspecific with each other cannot be confirmed, but the unique color combination and otherwise largely matching descriptions suggests they are conspecific; they differ most in the length and angle of R 2+3 (shorter and more divergent from R 4+ 5 in male), though this may just be intraspecific variation as this vein shows considerable intraspecific variation in the similar bibionid genus Penthetria ( Fitzgerald 2021) . Based on these considerations, the male is tentatively treated here as P. marginata and used to provide the first description of the male.

Redescription. Female (redescription based largely on notes from examination of holotype and paratypes in 1998 with additions, based on female from Colombia, given in braces {}): Coloration. Head black. Pedicel and base of first antennal segment orange, remaining segments brown {to dark brown}. Scutum primarily matte dark brown to black with thin grey pruinosity. Lateral margins of scutum narrowly orange, humeral ridge orange, and scutellum orange with thin brown median stripe. Thoracic pleurae brown tinged with orange (becoming more orange ventrally), {postnotum orange}. Legs yellow-brown with apices of femora, tibiae and basal tarsal segments brown, distal tarsomeres entirely brown. Halter with base of stem orange, apical ½ of stem and knob brown {to very light brown}. Wing hyaline {to very slightly greyish}, veins light brown {to orangish}, anteriors more strongly pigmented. Stigma light brown {to brown}. Abdomen orange-brown {to dark brown}. Head. Rather wide, three ocelli and tubercle present. Median line of frons somewhat carinate with two small round tubercles; ridge extending about half-way from antennal base to ocellar tubercle. Median ridge of frons strongly developed in one of the paratypes ( MNHN). Face scarcely developed; produced about width of one flagellomere length beyond antennal base. Clypeus + proboscis black, broad, short, {about as long as long axis of eye}. Nine flagellomeres, apical flagellomere minute nipple-like. Thorax. Katepisternum with a patch of setae. Legs. Hind tibia slender, hind basitarsus slender, long, about eight times as long as wide (twelve times as long as wide in BMNH paratype). Legs with short dark hair. Wing. Wings seem disproportionally long for the body size. Wing 10.5–12.0 mm, {14.5 mm}. R 2 +3 1/3 length R 4 +5, r-m ¼ length stem of M fork. {Venation typical for the genus ( Fig. 12 )}. Terminalia. Tergite nine much broader than long, with a short triangular median point on posterior edge .

Description. Male. Coloration. Head black. Apex of pedicel and very base of first antennal segment orangish, remaining segments dark brown. Scutum matte orange in ground color with three broad, matte, light brown stripes which are nearly contiguous with each other; very thinly separated by orange tint along dorsocentral grooves and median stripe medially longitudinally subdivided by thin orange line in median groove. Scutum with, lateral areas, humeral ridge, area just posterior to humeral ridge, scutellum, and area just anterior to scutellum orange. Thoracic pleurae largely orange except light brown dorsally. Legs yellowish with extreme apices of femora, tibiae (very subtly so) and basal tarsal segments light brown, distal tarsomeres entirely brown. Legs with dark hairs. Halter with base of stem orange, apical ½ of stem and knob brown. Wing hyaline to very light greyish, veins light brown, anteriors more strongly pigmented. Pterostigma light brown. Abdomen dark brown with pale hairs. Head. Three ocelli and tubercle present. Eye holoptic. Face not produced. Clypeus rectangular, about twice as long as wide. Clypeus + proboscis black, broad, short. Antennae with eight or nine flagellomeres (difficult to count as antennae are strongly shriveled), apical flagellomere minute nipple-like (at least on one antenna). Palps with four or five segmented (shriveled and hard to determine). Thorax. Mesonotum largely bare with short, very sparse, pale setae near subtle median and deeper dorsocentral grooves as well as laterally. Katepisternum with patch of dorsal setae. Legs. Long and slender, hind tibia and basitarsus nearly parallel-sided. Hind basitarsus about eight times as long as wide. Wing. 11.0 mm. R 2+3 1/4 length R 4+5. Venation typical for the genus ( Fig. 13 ). Abdomen. Terminalia ( Figs. 14–17 ). Epandrium (tergite nine) short, distinctly broader than long, posteromedial cleft broadly V-shaped with a small median triangular lobe, main posterior lobes of epandrium somewhat triangular but apically rounded. Anteromedial cleft of epandrium broad, U-shaped, extending about 1/3 length of sclerite. Gonocoxites ventrally broader than long, lacking posteromedian cleft and sclerotized median projection, though a pair of small rounded, setose, submedian lobes present that form part of the gonostylar socket. Lateral lobes of gonocoxites present, broad and broadly rounded apically in posterolateral view. Gonostylus simple, long digitate, slightly arched and gradually tapering apically to an acute point; posterior surface of gonostylus laterally compressed, fin-like, so that gonostylus appears much more robust (seagull-head-shaped) in posterolateral view than posterior view and appears acute in ventral and dorsal views (when fin is being view head-on).

Diagnosis & Remarks. The unique color of the mesonotum (dark medially with continuous orange border) and large size makes this species distinctive, but the shape of the gonostylus will distinguish it from other species, such as P. boliviana Fitzgerald , with similar terminalia. P. marginata belongs to the nigra -species-group (see Discussion).

Distribution. Previously known only from a high elevation type locality near the Ecuador / Colombia border. Newly reported specimens are from high elevation (páramo) sites in Colombia.

Figures

FIGURE 13. P. marginata Edwards, male, dorsal. Scale bar = ca. 1.0 mm.

FIGURES 10–12. P. marginata Edwards, female. 10. Habitus. 11. Thorax, dorsal. 12. Wing. Scale bars = ca. 1.0 mm.

FIGURES 14–17. P. marginata Edwards, male terminalia. 14. Dorsal. 15. Ventral. 16. Posterior. 17. Posterolateral. Scale bar = ca. 0.5 mm. Abbreviations: c, cerci; ea, ejaculatory apodeme; gc, gonocoxite; gs, gonostylus; llgc, lateral lobe of gonocoxite; t9, tergite nine.