Trigonocera pilifer, Grootaert & Velde & Isabella Van de, 2024

Grootaert, Patrick, Velde, & Isabella Van de, 2024, New long-legged flies from mangroves on Pulau Ubin (Singapore) (Insecta: Diptera: Dolichopodidae), Raffles Bulletin of Zoology 72, pp. 303-323 : 310-312

Trigonocera pilifer , new species

( Figs. 6 , 7 )

Type material. Holotype male. Singapore, Pulau Ubin , 29 March 2018, PU14 , secondary forest (Ma 9841, leg. P. Grootaert; in ethanol LKCNHM).

Paratypes. Singapore, Pulau Ubin , 5 males, 29 March 2018 station, PU14 (Ma 9841, leg. P. Grootaert; LKCNHM). 1 male dissected and figured; female, PU13 , ZRCBDP0257677 , 29 March 2018; GenBank accession code: PP893297; male, PU13 , ZRCBDP0281269 , 7 June 2018; male, Botanic Gardens ( CUGE) ZRCBDP0276806 , 10 November 2017; male, Bishan-Ang Mo Kio Park ( BAP01 ) ZRCBDP0275497 , 3 June 2018; GenBank accession code: PP893298; female, Prince Georges Park, ZRCBDP0041193 , 20 May 2015; GenBank accession code: PP893299; male, Pulau Semakau ( SM03 ) ZRCBDP0105383 , 23 January 2014, GenBank accession code: PP893300 .

Diagnosis. A medium-sized species (3 mm). Scape with bristles above. Propleural bristle short. Fore tarsus with claws and minute pulvilli. Metepimeron and basal tergite yellowish brown, tergites 2–3 whitish.

Etymology. The new species is named ‘pilifer’ after the bristles that are present on the first antennal segment (scape).

Male. Length: body 2.9 mm; wing 2.4 mm.

Head. Frons very wide, anteriorly nearly twice as wide as base of postpedicel. Face narrower than frons, face at base as wide as base of postpedicel, narrowing downwards. A pair of long retro- and lateroclinate ocellars, followed by a pair of short, weak proclinate basal ocellar bristles (¼ length of the anterior bristles). A pair of short postvertical bristles. A pair of strong proclinate vertical bristles nearly as long as the anterior ocellars. Upper postocular bristles short, black, and uniserial above, below only a little longer, white, and longest only near mouth. A few pale additional bristles behind the row of postoculars.

Antennae. Dark brown ( Figs. 6 , 7A–C ). Scape longer than pedicel, dorsally with a few bristles, half as long as scape. Pedicel with a dorsal bristle as long as pedicel is wide. Inner apical margin projecting inside base of postpedicel. Postpedicel triangular, nearly 2 times as long as wide at base, with the ventral margin widely overlapping the pedicel. Arista subapical, inserted a little beyond middle of dorsal margin of postpedicel. Palpus white, with a black apical bristle rather strong and half as long as palpus, in addition a few fine short hairs.

Thorax. 7 pairs of short fine acrostichals in anterior ⅔; 5 long dorsocentrals, anterior 3 equally long, posterior 2 bristles 1.5 times as long as preceding; prescutellar a little outside the row of dorsoventrals. 2 strong marginal scutellars with a tiny hair at outside. A short, fine propleural black bristle (not as prominent as in T. ubinensis , new species).

Legs. Entirely yellow, except for the brown mid and hind coxae. All bristles black.

Fore legs. Coxa with 3 long black anterior bristles in apical half, a few minute bristles, and 2 short apical bristles. Femur with 2 preapical posteroventrals as long as femur is wide; 1 short preapical posterior, a row of fine ventral bristle, 3 ventrals near middle longest, nearly half as long as femur is wide. Tibia lacking distinct bristles except from the weak bristles in the apical crown; a dense set row of fine pale bristles located ventrally, nearly as long as tibia is wide. A pair of small claws and indistinct pulvilli.

Mid legs. Coxa with an exterior black bristle at base as long as coxa is high and a shorter exterior near apex; anteriorly set with long bristles. Trochanter with 2 black anterior bristles, longer than trochanter is long, apical most bristle longest. Femur with a row of posteroventral bristles in apical half, as long as femur is wide. No anterior preapical bristle. Tibia with a short anterodorsal near base and 2 shorter dorsal bristles near middle; bristles in apical crown strong but not much longer than width of apex of tibia. A pair of small claws and minute pulvilli.

Hind legs. Coxa with a long exterior at base, as long as coxa is high and 1 or 2 minute bristles near apex. Trochanter with two long anterodorsal bristles. Femur lacking an anterior preapical, but with a preapical av about as long as femur is wide; no other distinct bristles (no ventrals). Tibia with 2 short dorsal bristles in apical half, and an apical crown of rather short bristles. A pair of short claws and minute pulvilli.

Wings. Hyaline with a faint brownish tinge, veins brownish. Veins R 4+5 and M 1+2 running parallel over entire length, M 1+2 straight (lacking a weak bent near middle). Squama dusky with very long black bristles, dorsal paler. Haltere white. Metepimeron brownish.

Abdomen. Tergite 1 pale brown, tergites 2–3 yellowish white, but all 3 tergites dorsally with apical border brownish. Tergite 4 with a yellowish spot at side. All tergites with short dorsal bristles and long apical bristles, except tergite 6 which lacks bristles. Sternites 1–3 yellowish white; sternites 4–5 brown. Sternites 2–4 each with very short black bristles, and a pair of somewhat longer apical bristles; no apical bristles on sternite 5.

Male terminalia. Fig. 7 . Cercus pale brownish including the rounded basal lobe that bears black bristles, the ventral appendage at least 2 times as long as rounded part, with a few bristles located dorsally, apical pair of bristles strongest ( Fig. 7F ). Dorsal surstylus tubular, hidden by the ventral surstylus, bearing a long apical bristle. Ventral surstylus brown, long, narrowing toward tip ( Fig. 7D ) with only a few minute hairs near apex. Postgonite with a rectangular bent near base and a rounded, rectangular bent near middle ( Fig. 7E ). Epandrial lobe, elongate rectangular with a long bristle inside its base and 2 closely set apical bristles ( Fig. 7F ).

Female. Unknown. Probably not recognised because it was confused with similar-looking Diaphorus females that also have a shorter, non-triangular postpedicel.

Comments. Trigonocera pilifer , new species, is quite peculiar in having distinct dorsal bristles on the scape. In the world key recently made by Liu et al. (2018), the new species would run to T. lucidiventris Becker, 1922 in having pale basal tergites. Olejníček (2004) revised the type material and made a re-description and illustrations of this species. The scape does not bear dorsal bristles ( Olejníček, 2004; fig. 1) and the postpedicel is shorter in the new species but elongate triangular in T. lucidiventris . The base of the postpedicel is truncate, while in the new species it has a wide ventral lobe over the pedicel ( Fig. 7B, C ). It is not clear if the pedicel has a thumb-like projection into the base of the postpedicel. The epandrial lobe is much narrower ( Olejníček, 2004; Fig. 4 ) than in Trigonocera pilifer , new species, but unfortunately the postgonite was not illustrated.

Trigonocera specialis Becker, 1922 that also has pale basal tergites, has enlarged pulvilli on the fore tarsus. According to Olejníček (2004), who also gave a re-description of this species, the scape is bare and the postpedicel is nearly 3 times as long as wide, somewhat onion-shaped at its base with a long narrow apex ( Olejníček, 2004; Fig. 9 ). The epandrial lobe is very narrow bearing a pair of very long bristles.

National distribution. Barcoding allowed for the identification of formerly unrecognised specimens that seem to have a wide distribution not limited to mangroves alone. Trigonocera pilifer , new species, is presently known from Pulau Ubin, Pulau Semakau, and the more anthropogenic habitats at Prince Georges Park (PGP), Bishan-Ang Mo Kio Park, and the Botanic Gardens (CUGE).

Comments. Apart from the triangular postpedicel in males and the attachment of the postpedicel on the pedicel, the differences between Diaphorus and Trigonocera remain subtle. In Trigonocera , the postgonite has a dorsal rectangular bent near its middle (see Figs. 7 and 9 ), while the postgonite is generally not so strongly bent near its middle in Diaphorus . This character, however, needs further verification.

Figures

Fig. 6. Trigonocera pilifer, new species, male habitus (Ma9841, Pulau Ubin). Photograph by Isabella Van de Velde.

Fig. 7. Trigonocera pilifer, new species, male. A, Antenna outside; B, Postpedicel outside; C, Postpedicel inside; D, Dorsal and ventral surstylus; E, Postgonite and dorsal surstylus; F, Hypopygium lateral view. Scale bar = 0.1 mm. Drawings by P. Grootaert.

Fig. 4. Chrysotus ubinensis, new species. A, Habitus paratype male (Ma6107). B, Paratype female (Ma6107). Photographs by Jayanthi Puniamoorthy.

Fig. 9. Trigonocera ubinensis, new species, male. A, Antenna outside with detail of apex postpedicel; B, Eighth sternite; C, Postgonite; D, Hypopygium lateral. Scale bar = 0.1 mm. Drawings by P. Grootaert.