Pseudohercostomus singaporensis, Grootaert & Velde, 2021

Grootaert, Patrick & Velde, Isabella Van de, 2021, Understanding the tangled taxonomy of the genus Pseudohercostomus Stackelberg, 1931 (Insecta: Diptera: Dolichopodidae) with description of new species from Singapore and DR Congo, Raffles Bulletin of Zoology 69, pp. 324-335 : 325-330

Pseudohercostomus singaporensis , new species

( Figs. 1–3 , 6C )

Diagnosis. Medium-sized species (4.8–5.2 mm) with biserial acrostichals and five dorsocentrals. Scape yellow. Postpedicel a little shorter than high, not triangular, with a broadly rounded apex. Mid coxa yellow except for a black anterodorsal stripe. Ventral surstylus with only three ventral bristles (at least eight long bristles in P. echinatus ). Female with multiple rows of small spinules on the ovipositor, the spines are smaller than in P. congoensis , new species.

Type material. Holotype male: SINGAPORE: Kranji Marshes , KM04 , 1°25′11.00″N 103°43′54.30″E, 2 April 2019, alt. 5 m asl, Malaise trap inside swamp forest (leg. P. Grootaert; ZRC _ BDP0243029 , ZRC).

Paratypes: SINGAPORE: 2 females, Kranji Marshes , KM04 , 1°25′11.00″N 103°43′54.30″E, 2 April 2019, alt. 5 m asl, Malaise trap inside swamp forest (leg. P. Grootaert; ZRC _ BDP0243028 (imaged) & ZRC _ BDP0371544 ) ; 1 female, Kranji Marshes , KM04 , 1°25′11.00″N 103°43′54.30″E, 29 May 2019, (Ma 11375; leg. P. Grootaert; ZRC _ BDP0371545 , dissected. ZRC) ; 2 females, Kranji Marshes , KM03 , 1°25′12.00″N 103°43′51.00″E, 10 April 2019 (Ma 11304, leg. P. Grootaert; ZRC _ BDP0371546 & ZRC _ BDP0371547 ) , alt. 5 m asl, Malaise trap along border of a swamp forest ( ZRC) ; 1 male, Kranji Marshes , KM05 , 1°25′10.15″N 103°43′53.53″E, 16 April 2019, (Ma 11326; leg. P. Grootaert; ZRC _ BDP0371548 ) alt 5 m asl., Malaise trap inside swamp forest ( RBINS) .

Other material examined. CAMBODIA: 1 male, Siem Reap, Preah Khan , 24 January–21 February 2006 (in coll. RBINS) .

Description. Male ( Figs. 1 , 3 ). Length: body 5.3 mm; wing 4 mm.

Head. Frons metallic green, wide, parallel-sided hardly narrowing towards antennal sockets. Face wide, metallic green, microtrichose, parallel-sided, clypeus distinctly separated, about ⅓ length of face; brown at base while yellowish on apical half. All bristles and hairs on head black. A pair of strong anterior ocellar bristles, retroclinate, half as long as height of an eye. Vertical bristle on border with occiput, as long as ocellars. A pair of long postverticals, half as long as verticals. Occiput black in ground-colour with a row of rather long, uniserial, black postocular bristles. Postocular row ends below in a single long bristle, curved around the proboscis, 2× as long as the lower postoculars. Behind row of postoculars bristles a few long, black bristles.

Antenna yellowish brown. Scape yellow, lacking dorsal bristles, with a long inner, apical projection. Pedicel half as long as scape with an apical row of black bristles; a long dorsal apical bristle twice as long as pedicel, dorsally a second row of bristles. Ventral apical bristles longer than those at the side. Postpedicel yellow in ground-colour, but with a brownish tinge, especially near tip due to dense dark microtrichia. Postpedicel a little higher than long (0.16/ 0.18 mm) with a broadly rounded tip. Arista black, 2–2.5× as long as postpedicel set with fine diverging hairs. Proboscis yellowish brown with short dark hairs and a pair of long fine black hairs, 2× as long as pseudolabellae are broad. Palpus yellowish with short black bristles and a little stronger subapical bristle.

Thorax blackish green in ground-colour. Mesoscutum on anterior quarter, densely and uniformly set with short black bristles, the dorsocentral bristles are not distinct in that area. A strong humeral bristle, a long posthumeral; in between dorsocentrals and notopleurals three shorter bristles that might represent sutural and postsutural bristles. Three notopleurals (middle notopleural on border with pleura, longest). A long supra-alar and a postalar. Five black dorsocentrals on posterior ⅔ of mesoscutum. Anteriormost dorsocentral bristle short and fine, other four becoming longer towards scutellum. Apical dorsocentral longest and a little outside of the row. Acrostichals black, 10 biserial pairs reaching almost to scutellum. Scutellum distinctly rectangular with on each apical corner a very long scutellar bristle and a small bristle at the outside. Pleura black with a metallic green shine, microtrichose. A single short black upper propleural bristle and a very strong black lower propleural bristle inserted on border of fore coxa. Metepimeron very large, with a wide lateral lobe pushing sternite 1 aside ( Fig. 1 ).

Legs yellow except for mid coxa having a brown streak anteriorly and a small black patch on the middle. Tarsi are yellow in ground-colour but look dark due to dense black bristling.

Fore leg. Coxa rather broad, anteriorly densely and uniformly set with short black bristles, at base a transverse row of slightly longer bristles; a row of strong apicals longer than coxa is wide; four strong bristles on posterior border, basal bristle pointing outward. Trochanter lacking bristles. Fore femur shorter and nearly half as wide as mid femur; fore femur anteriorly uniformly set with short bristles, a short preapical anterior as long as femur is wide at apex; a row of long, fine ventral bristles longest near base as long as femur is wide, bristles further decreasing in length towards apex while in apical quarter three bristles are pointing downward. A single fine preapical posteroventral bristle as long as femur is wide and a smaller preapical posterior.

Tibia a little shorter than femur. Apical fourth with five orange anteroventral crests being insertion sites of combs of fine short pale bristles. Five strong dorsals and three even stronger anterodorsal bristles being 3× as long as tibia is wide. Anterodorsally lacking short bristling except for extreme base and apical fifth.

First tarsomere as long as following four tarsomeres, ventrally densely set with bristles as long as tarsomere. Tarsomeres 2–4 with a produced ventral apex bearing a pair of bristles as long as tarsomere. Tarsomere 5 with a pair of distinct back claws and small pulvilli.

Length of femur, tibia, tarsomeres (in mm): 1.03: 0.97: 0.55: 0.16: 0.11: 0.13: 0.16.

Mid leg. Coxa broad, as a shield over the base of the femur, covering the small trochanter. Coxa anteriorly densely covered with black bristles, apical, dorsal, and ventral borders with long bristles (about ½ as long as coxa is high) and a strong bristle midway the dorsal border as long as coxa is high. Exterior bristle lacking.

Femur twice as wide as fore femur; laterally flattened, anteriorly and posteriorly densely covered with short bristles. A very strong anterior preapical bristle, preceded by a shorter one. Ventrally with a row of black bristles nearly as long as femur is wide; bristles are fine at base but becoming stronger towards apex of femur.

Tibia anterodorsally lacking short bristling except for extreme base and apical fifth; a row of anterodorsal and posterodorsal bristles becoming very strong towards apex of tibia ( Fig. 1 ) strongest on apical third, 4× as long as tibia as wide. A strong ventral bristle on apical third (4× as long as tibia is wide). Apical crown with very strong bristles (ventral and dorsal bristle 2× as long as tibia is wide). Tarsomeres 1–4 with anterodorsal rows of combs of short black bristles: from tarsomere 1 to 4 respectively: 11, 8, 6, 4–5 rows. Bristling on tarsomere 5 dense and not organised in rows. Tip of tarsomeres 1–4 ventrally produced and bearing a pair of strong bristles. Length of femur, tibia, tarsomeres (in mm): 1.58: 1.74: 0.87: 0.51: 0.41: 0.32: 0.19.

Hind leg. Coxa with a fine exterior bristle inserted near apex of coxa, nearly as long as coxa is high, with a minute bristle at its base.

Femur a little wider than mid femur, laterally flattened, anteriorly and posteriorly densely covered with short bristles. Dorsally with a dense row of long bristles being half as long as femur is wide. A strong anterior preapical bristle, preceded by a short one. Ventrally with a row of black bristles nearly as long as femur is wide, bristles are fine at base but becoming stronger toward apex of femur.

Tibia comparable to mid tibia: anterodorsally lacking short bristling except for extreme base and apical fifth; a row of anterodorsal and posterodorsal bristles becoming very strong towards apex of tibia, with a ventral row of bristles,

about as long as tibia is wide in basal third becoming very strong in middle.

Tarsomeres 1–4 with anterodorsal rows of combs of short black bristles: from tarsomere 1 to 4 respectively: 12, 11, 10, 9–10 rows. Bristling on tarsomere 5 dense, not organised in rows. Tip of tarsomeres 1–4 are ventrally produced and bearing a pair of strong bristles. Apical tarsomere with a pair of black claws a little longer than tarsomere is wide and a pair of dorsal strong bristles as long as claws (giving the impression that there are four claws). A pair of short pulvilli with an empodium.

Length of femur, tibia, tarsomeres (in mm): 1.9: 1.82: 0.71: 0.60: 0.4: 0.22.

Wing greyish tinged with black veins. Base of costa widened and densely set with small bristles. Vein R 4+5 and M only weakly diverging towards wing tip. Posterior crossvein nearly 2× as long as apical section of Cu. Squama white with multiple rows of black bristles and a row of long black marginal bristles. Haltere white.

Abdomen with five externally visible segments. Tergite 1 narrow with a row of bristles on basal border, longest at sides, two rows of shorter bristles on disk and a row of equally long marginal bristles. Tergite 2–5 densely set with short bristles on disk (about five rows) in addition with a row of marginal bristles twice as long as those on disk. Each of tergites 2–5 has four longer and stronger marginals as long as tergite is long. Sternum with only three visible sternites. Sternite 1 lacking and sternite 5 hidden under sternite 4. All sternites densely set with short back bristles.

Male terminalia small and hidden ( Fig. 1 ). Cerci yellow with pale hairs while surstyli are shiny brown. Tip of hypandrium with a small downturned point ( Fig. 3H ). Basoventral epandrial bristle long, close to base of hypandrium ( Fig. 3A, B, H ). Apicoventral epandrial bristle short, inserted on a short papilla, probably representing the reduced apicoventral epandrial lobe. Ventral surstylus bears a thickened apical bristle pointing inward ( Fig. 3D, H ), a longer preapical and two minute bristles. Tip of dorsal surstylus bears a subapical short black spine inserted at the inside in a shallow furrow ( Fig. 3E, F ). A long internal lobe is present on the dorsal surstylus and reaches slightly beyond tip of dorsal surstylus ( Fig. 3D, G ).

Female ( Figs. 2 , 6C ). Length: body: 4.8 mm; wing: 4.16 mm. Female in most characters similar to male but the ventral bristles on hind femur seem to be shorter. Acanthophore dorsally covered by several rows of strong acanthae (spinules). Only a single bristle present behind the rows of acanthae ( Fig. 6C ).

Etymology. The new species is named after the type locality, Singapore.

Comments. Being more or less sympatric, the new species should be compared with P. echinatus Stackelberg that was originally described from Lambogan (Java) and later reported from Bogor ( Parent, 1934) and Jakarta ( Hollis, 1964). All these sites are on Java, Indonesia. The main difference between P. singaporensis , new species, and P echinatus is the presence of biserial acrostichal bristles on the mesoscutum which are instead quadriserial in P. echinatus . Stackelberg (1931) also mentions that the postpedicel is triangular (dreieckig), hardly longer than high with a distinctly pubescent arista near the middle of the dorsal border. The postpedicel in the new species is a little shorter than high, not triangular, but with a rounded tip. Stackelberg further mentions that the male has only four distinct dorsocentral bristles. In the new species there are five dorsocentrals with the most basal dorsocentral short and fine, while the following dorsocentrals are much stronger. The male terminalia are also slightly different in the two species: the ventral surstylus bears only three ventral bristles in the new species while there are at least eight long bristles in P. echinatus .

Distribution. Singapore, Cambodia.

Habitat. The new species was found in several sites in a swamp forest in Kranji Marshes, Singapore ( Fig. 4 ). These marshes were formerly part of a mangrove ecosystem that was dammed in the seventies and turned into a freshwater swamp with lakes, swamp forest, and secondary forest ( Grootaert, 2020).

In general, it seems that the genus Pseudohercostomus is linked to freshwater habitats. The type species of the genus, P. echinatus was originally found as a puparium between the roots of water hyacinth ( Eichhornia ), and the male that emerged from it was described by Stackelberg (1931). The association with the water hyacinth is not yet clear. Anyway, water hyacinth was present in the lakes of Kranji marshes but not inside the swamp forest itself where the new species was found. Water hyacinth was also present in the site of Preah Khan in Cambodia very close to where the Malaise trap was installed in which we also collected P. singaporensis , new species. The Afrotropical species P. congoensis , new species, was collected on the borders of Lake Edward and its tributaries. We do not know if there was a link with water hyacinth in that case. What is intriguing is the morphology of the ovipositor that bears multiple rows of strong spinules (acanthae). This might indicate that the ovipositor is used to scrape a substrate during egg laying and is not simply used for moving a granulated substrate.

Figures

Fig. 1. Pseudohercostomus singaporensis, new species, male habitus. Paratype (Kranji Marshes, KM04 (ZRC_BDP0243029, ZRC)). Photo credit: Rene Ong. Abbreviation: metep: metepimeron.

Fig. 2. Pseudohercostomus singaporensis, new species, female habitus. Paratype (Kranji Marshes, KM04 (ZRC_BDP0243028, ZRC)). Photo credit: Rene Ong. Abbreviation: metep: metepimeron.

Fig. 3. Pseudohercostomus singaporensis, new species, male terminalia. Holotype (Kranji Marshes, KM05). A, ventral view hypopygium; B, lateral view hypopygium; C, eighth sternite; D, ventral view of epandrial lobe, ventral surstylus and dorsal surstylus; E, tip of dorsal surstylus from inside; F, tip of dorsal surstylus from outside; G, tip of inner lobe of dorsal surstylus; H, tip of hypopygium lateral; I, dorsal view of cerci and dorsal surstyli. Abbreviations: apv: apicoventral epandrial bristle; bv: basoventral epandrial bristle; cerc: cercus; dsur: dorsal surstylus; ejap: ejaculatory apodeme; hyp: hypandrium; idsur: inner lobe of dorsal surstylus; vsur: ventral surstylus. Scale bar = 0.1 mm.

Fig. 6. Pseudohercostomus. A, P. congoensis, new species, holotype male terminalia lateral view; B, P. congonesis, new species, female left acanthophore and cercus dorsal view, paratype; C, P. singaporensis, new species, acanthophore dorsal view, paratype (Kranji Marshes). Scale bars = 0.1 mm.

Fig. 4. Habitat of Pseudohercostomus singaporensis, new species, in Kranji Marshes. A, site KM05 inside the swamp forest in the beginning of the rainy season. B, site KM03 at the border of the swamp forest at the end of the rainy season. (Photo credit: P. Grootaert)