Formosargus James 1939
Creators: name: Fachin, Diego Aguilar
name: Hauser, Martin
Publisher: name: Zenodo
Year: 2022
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Stratiomyidae
Formosargus

description: Formosargus James, 1939
(Figures 1–26)
Formosargus James, 1939: 35.
Type species: Formosargus kerteszi James, 1939, by monotypy.
Amsaria Adisoemarto, 1974: 69. Type species: Amsaria sagittocera Adisoemarto, 1974, by original designation. Syn. nov.
Diagnosis
Dichoptic eyes in both sexes (Figures 3–6). Ocellar tubercle often reduced in size, as wide as vertex area or much narrower (Figures 3–4); upper frons short, wider than long, at most only slightly longer than wide; lower frons often longer than upper frons (Figures 5–6). Male mid legs with a modified structure at base of first tarsomere (Figure 8). M4 vein branches off from discal cell, with m–cu crossvein connected at M3+4 fork (Figure 9); M1 and M3 long, but often fading, only apparent basally or as a fold (Figure 9 (a)). In male genitalia, gonocoxal apodeme reduced, not discernible; gonocoxal bridge at distal third; phallus and parameral sheath very reduced (Figure 10). Male and female mainly differing in the colouration over thorax and abdomen, with scutal bands slender and less intense and abdomen often completely yellowish in females; frons, frontal callus, and face in females broader than in males.
Redescription
Male. Length (mm): body, 6.0–6.5; wing, 5.5–6.0. Head (Figures 3–6). Typical of sargines, higher than wide and concave in dorsal view; eyes dichoptic, with very few sparse and minute setae on the eyes, and ommatidia uniform in size, except for a roughly circular area with slightly bigger ommatidia frontally. Frons, frontal callus, and face width nearly one-fifth of head or less, margins parallel-sided. Occiput black. Vertex area (from the posterior ocellus to the margin of the occiput) wide, mostly white to yellowish, except for a thin dark brown line on each side laterally; pilosity often yellowish, short to medium in length. Ocellar tubercle dark brown to black at centre, yellowish or brownish externally, reduced in size, often as wide as vertex or shorter; ocelli in the form of equilateral triangle; pilosity often yellowish, denser than in vertex, short to medium in length. Upper frons (black area between anterior ocellus and white lower frons) often wider than long or at most slightly longer and at least twice shorter than lower frons (whitish part above antenna); medial area of upper frons yellowish or brownish, at least twice as slender as the lateral area; black lateral area width varying from short to as wide as ocellar tubercle width, with short and dense yellowish to darkish pilosity; shape of anterior margin of upper frons at edge with lower frons: inverse-U-shaped (e.g. Figure 5 (a)), straight to nearly straight (Figure 6 (d))) or U-shaped, with median triangular extension slightly (Figure 6 (e)) to strongly (Figure 5 (f)) pointing towards antennal insertion. Frontal callus (= upper part of the lower frons) not distinguishable from basal half of lower frons in colour; latter with short whitish pilosity near antenna insertion. Antennae inserted at basal third of head; scape slightly longer than pedicel; mostly yellowish to reddish brown, except for a dorsoapical arista-like terminal flagellomere often dark brown, longer than remaining antenna, with a few setae at base, but often with only two; basal four flagellomeres compact, with short, relatively dense, yellowish hair-like setae; fourth flagellomere rounded or subtriangular, as long as each previous flagellomere separately (Figure 2 (a, b)) or much longer (Figure 2 (c)). Face white to yellow, much shorter than lower frons, pilosity short, yellowish. Proboscis whitish to reddish yellow, labellum well developed; maxillary palpus short, twosegmented, distal segment enlarged and shorter than basal segment. Thorax (Figure 7). Scutum mostly pale yellow in background, but reddish in some species; with a varied pattern of dark brown markings, ranging from a single complete medial band over scutum (e.g. Figure 7 (a)), with or without additional anterior and posterior lateral bands (e.g. Figure 7 (h)), to a completely dark scutum (Figure 7 (i)); scutellum often marked with dark brown, at least in the centre. Pleuron pale yellow to reddish yellow in background, with anepisternum, katepisternum, laterotergite, and mediotergite often marked with dark brown; pilosity white to yellow. Legs varying from whitish to reddish yellow, with at least the last three to four hind tarsomeres often dark brown; virtually unmodified, except for hind leg with first tarsomere much longer than tibia, and a modified structure at apex of mid first tarsomere, often hook-like or coiled, unique for each species (Figure 8). Wing (Figure 9). Wing membrane hyaline, with brownish veins; only microtrichia over membrane, except on alula, basal area of cup and br, bm, and cua cells anteriorly. C ending at wing tip. R2+3 originating slightly before or at level of r–m crossvein; basal third of R2+3 often curved, apical two-thirds straight, parallel to R1 towards wing margin. R4 weakly curved at base, arising from R5 with almost right angle, nearly straight on apical twothirds. R5 slightly curved posteriorly, ending posterior to wing tip. M fading on nearly entire extension between bm and br cells, except on its extreme apical portion; distal branch of M1+2 longer than proximal branch of M1+2; m–m as long as short branch of M3; M1 and M3 weakly developed compared to M2, often discernible proximally or as a fold; M4 connected to discal cell; r–m as long as R4; m–cu crossvein connected to M3+4 fork. Medial branches often not reaching wing margin. Cu vein basal to true cubital fork only setose on its basal half. Alula narrow, without microtrichia. Halter pale yellow to yellow.
Abdomen. Pale yellow to reddish yellow in background, with at least a pair of roughly subrectangular dark brown spots on tergite 1, and tergites 2–5 mostly yellowish, with a pair of proximal or medial dark brown spots to nearly entirely dark; more than twice longer than broad, wider at about fourth segment; first segment slightly shorter than remaining segments, parallel-sided; divergent margins on segments 2–4, convergent margins on segment 5; pilosity short and yellowish. Terminalia (Figures 10–14). Genital capsule subrectangular, slightly taller than wide; distal margin weakly developed dorsally, exceeding ventral margin height; ventral margin of synsternite clearly U-shaped, often with projections medially; synsternite with a pair of well-developed inner projections, ventral to phallus, curved at base, parallel on distal two-thirds. Gonocoxal apodeme very reduced; gonocoxal bridge placed at distal margin of genitalia. Phallus trifid, with very shortened lobes; parameral sheath roughly elliptical or subrectangular, nearly entirely encapsulating the phallus; both very reduced in size, placed at distal half of genitalia. Gonostylus wide, varied in shape, with expansions or bilobed. Epandrium wider than long. Proctiger (tergite 10) well developed, as long as cercus, triangular; cercus slender, rodshaped.
Female. Similar to male, except as follows: Length (mm): body, 5.0–10.0; wing, 5.0–9.0. Head (Figures 3–6). Frons, frontal callus and face wider than one-fifth of head. Face much shorter than lower frons or at most as long as. Thorax (Figure 7 (b, e–g)). Scutal bands or maculae over scutum often slender and less intense in colour.
Abdomen. Mostly pale in colouration, varying from completely yellow to well maculated with dark brown on each visible tergite at centre or distally; spots of tergites 2– 5 often weakly or not connected medially; clearly oval, with divergent margins on segments 1–2, parallel margins on segment 3, convergent margins on segments 4–5. Terminalia (Figures 15–17). Typical of sargines, mostly differing in the shape of genital fork. Tergite 8 rectangular, nearly twice longer than wide; sternite 8 wider than tergite 8, subtriangular on its distal fourth. Tergite 9 sclerite strongly chitinised laterally. Genital fork (sternite 9) often wider posteriorly, with anterior half gradually (Figure 17 (a)) or only basal third abruptly (Figure 17 (c)) narrowing into an often straight anterior end; posterior bridge from nearly straight (Figure 17 (k, l)) to weakly bilobed (e.g. Figure 17 (i, j)); posterolateral process curved at basal third, parallel on apical two-thirds; genital opening reduced, from elliptical to nearly circular-shaped, displaced posteriorly on the genital fork. Tergite 10 well developed, triangular. Cercus two-segmented; first segment of cercus nearly twice as long as second segment.
Geographic distribution
Oriental Region: Taiwan (Pingtung; Orchid Island), Philippines (Benguet; Eastern Samar: Calicoan Island; Laguna; Palawan), Thailand (Trang), Malaysia (Pahang; Sabah), Indonesia (North Maluku: Island of Mangole; West Java); Australian Region: Indonesia (West Papua), Papua New Guinea (Morobe); Australia (Queensland) (Figure 26).
Comments
The Malagasy Gongrosargus Lindner, 1959 is the only other genus of Sarginae that has the M4 vein branching off from the discal cell in the wing, with m–cu crossvein connected to the fork of M3+4 (Hauser et al. 2017b, p. 965, fig. 182). These, however, are very large flies and distinct due to the presence of more than five antennal flagellomeres (see Hauser et al. 2017b, p. 957, fig. 130), while all remaining genera of Sarginae have only five. Therefore, this may indicate that the genus does not belong to the Sarginae, but may be instead more closely related to the Chrysochlorinae and Hermetiinae.
Adisoemarto (1974) compared his new genus Amsaria with the genera Sargus and Ptecticus and pointed out it could be distinguished from the latter two by the shape of the antenna, wing veins and thorax colouration. This is in part correct. Formosargus does not have a thumb-like projection of the pedicel towards the inner face of the flagellar complex as seen in Ptecticus (e.g. Rozkošný and Kovac 1994, p. 78, fig. 16); and in some species, including that described by Adisoemarto, the fourth flagellomere alone can be as broad as the remaining flagellomeres (see his p. 70, fig. 4), a feature that excludes it from Sargus as well. In respect of the scutum colour, the presence of a single medial dark band is indeed rather unique for most species of the genus, but some Formosargus species have also additional lateral markings, bands, or a completely dark scutum. In the Oriental Region, a three-banded scutum can be seen in Ptecticus, for example in P. proximus Rozkošný and Kovac, 1996. Therefore, this feature, the colouration of the thorax, is also not a good choice for genus identification. Adisoemarto, however, was not aware of James’s description of Formosargus (James 1939), nor of his second species described in 1969, in which he stated that the genus could be distinguished by the m–cu connected to the M3+4 fork and by veins M1 and M3 mostly fading. After examining photographs of the female holotype of Amsaria sagittocera (Figure 24) housed in the MZB collection and the illustrations in Adisoemarto (1974), it is clear to us that it belongs to Formosargus, and therefore, Amsaria is proposed as a new synonym of Formosargus.
The male genitalia, illustrated for the first the time in this paper, is rather unique in the Sarginae, distinct from the genitalia of the other genera worldwide. In some Sarginae, there is a medial line, sometimes only visible as a subtle scar, over the ventral face of the synsternite, basal to the gonostylus insertion, with different degrees of sclerotisation that may be evidence of the fusion between the gonocoxites. This condition can be seen in Acrochaeta and some Merosargus, where the medial line can be further modified into a highly sclerotised projection internally (e.g. Fachin and Amorim 2015, p. 91, fig. 335). In the three genera, this medial line on the synsternite is present, although it is not well marked externally in Formosargus as it can be in Acrochaeta and Merosargus species. The medial line is, then, in Acrochaeta, Formosargus, and in some Merosargus, connected to the inner walls of the synsternite (e.g. Figure 10 (b)); Fachin and Amorim 2015, p. 19, fig. 40 and p. 90, fig. 331)). Additionally, Formosargus shares with these two Neotropical genera the presence of an inner projection in the synsternite, but the condition is slightly different. The inner projection itself in Formosargus is rather long, parallel and well defined, sometimes with strong setae distally, and free of an innermost connection with the ventral or inner margins of the gonocoxite (Figure 11), while in some Merosargus and in some members of Acrochaeta (e.g. A. fasciata Wiedemann, 1830; see Fachin and Amorim 2015, p. 19, fig. 40), the inner projection is wide and simple, with no signal of reduction around the gonostylus, and in the other members of Acrochaeta (e.g. A. flaveola Bigot, 1879; see Fachin and Amorim 2015, p. 53, fig. 61), the inner projection is still platelike but reduced laterally and around the gonostylus. In Formosargus, both the phallus and the parameral sheath are highly reduced and displaced distally in the genitalia (see e. g. Figure 12 (a)), which may be related to the reduction of the gonocoxal apodeme as well, recognisable only by an enlarging at the centre of the gonocoxal bridge (see e.g. Figure 11 (a), see black arrow). These features have also not been found in other sargines and may be apomorphies for Formosargus as well.
Another important finding is the presence of a modified structure at the base of the first tarsomere in the male mid leg (Figure 8), which is, besides the hind tibial flange of Ptecticus kovaci Hauser and Rozkošný, 2007, the only case of a modified leg within Sarginae.Males are indeed rarer than females and only James (1939, 1969) had males to examine, but he did not notice the structure in the male mid leg. In the species of which we have males,the feature is unique for each species, which indicates it may be associated with some sort of courtship.
Key to the adults of the species of Formosargus
1. Scutum with only a dark brown medial band (Figure 7 (a–c)) extending onto scutellum, in one species with an additional notopleural macula (not to be confused with a dark macula on anepisternum); fourth flagellomere rounded, shorter than previous flagellomeres combined (Figure 2 (a, b)); last four hind tarsomeres completely yellow (Figure 18 (c)) ........................................................................................................................................ 2
- Scutum with additional dark markings beside the medial band and the notopleural macula (Figure 7 (h)), in some species scutum nearly completely dark (Figure 7 (d, i)); fourth flagellomere subtriangular, as long as previous flagellomeres combined (Figure 2 (c)); last four hind tarsomeres black (Figure 19 (a)) or completely yellow 8
2. Notopleuron with large black macula (Figure 7 (f)); male unknown; Malaysia: Borneo............................................................................................................. F. borneensis sp. nov.
- Notopleuron without black macula (Figure 7 (g)), pale yellow to yellow-orange, like most of the body ................................................................................................................................ 3
3. Mediotergite completely yellow (Figure 7 (g)), conforming with the colour of the body ......................................................................................................................................................... 4
- Mediotergite completely dark (Figure 7 (e)), contrasting with the colour of the body ................................................................................................................................................ 7
4. Anepisternum with black macula (Figure 20 (a)) .................................................................... 5
- Anepisternum without black macula (Figure 18 (c))............................................................. 6
5. Vertex area less than twice the length of the ocellar tubercle (Figures 3 (a), 22(a, e)); Taiwan; Philippines .................................. F. kerteszi James, 1939 [in part, only females]
- Vertex area at least twice the length of the ocellar tubercle (Figure 4 (c)); male unknown; Indonesia: Mangole Island .......................................... F. mangoleensis sp. nov.
6. Female abdomen completely yellow, without dark markings (Figure 18 (d)); male with a pair of dark markings on the lateral margins of tergite 1 (Figure 18 (b)); Papua New Guinea ................................................................................................ F. lineatus (de Meijere)
- Female abdominal tergites 2–5 each with a pair of diffuse dark markings (Lessard et al. 2020, p. 29, fig. 4); male unknown; Australia: Queensland ...... F. melanogrammus Lessard and Woodley
7. Black upper frons wider than long, anterior margin slightly inverse-U-shaped (Figure 5 (a)); scutal band less than one-third of the scutum width, wider on posterior half (Figure 7 (a)); Taiwan: main island; Philippines ......... F. kerteszi James, 1939 [in part, only males]
- Black upper frons as long as wide, anterior margin slightly pointed towards the middle (Figure 6 (a)); scutal band approximately one-third of the scutum width, more homogeneous in width, except at transverse suture (Figure 7 (e)); male only known from Figure 1; Taiwan: Orchid Island .............................................. F. berezovskiyi sp. nov.
8. Scutellum completely yellowish (Figure 7 (h)).......................................................................... 9
- Scutellum with dark markings (Figure 7 (i)), which can sometimes be diffuse and poorly defined................................................................................................................................... 10
9. Hind tarsomeres yellowish (Figure 25); Philippines: Palawan ..... F. variegatus James, 1969
- Second hind tarsomere white and last three dark brown (Figure 20 (c)); Malaysia, Thailand ........................................................................................................... F. trivittatus sp. nov.
10. Anterior margin of black frons to yellow lower frons straight (Figure 6 (f)); male frons extremely narrow, only slightly broader than ocellar triangle (Figure 6 (f)); female unknown; Philippines: Laguna ................................................................. F. woodleyi sp. nov.
- Anterior margin of black frons with median triangular extension pointing towards antennal insertion (Figure 5 (f)); frons wider, more than twice as broad as ocellar triangle (Figure 5 (f)); Indonesia: West Java .......... F. sagittocerus (Adisoemarto, 1974)
description: Published as part of Fachin, Diego Aguilar & Hauser, Martin, 2022, Revision of Formosargus James, 1939 (Diptera: Stratiomyidae): five new species in an otherwise rare genus and Amsaria Adisoemarto, 1974 as a generic synonym, pp. 1513-1562 in Journal of Natural History 56 (37 - 40) on pages 1517-1528, DOI: 10.1080/00222933.2022.2117107, http://zenodo.org/record/7318178