Hercostomus squamatus, Samoh & Grootaert, 2024

Samoh, Abdulloh & Grootaert, Patrick, 2024, New species and records of the genus Hercostomus Loew (Diptera: Dolichopodidae) from Thailand mangroves, with notes on the Hercostomus fauna of Singapore mangroves, Zootaxa 5446 (2), pp. 179-204 : 184-189

Hercostomus squamatus sp. nov.

( Figs 4–6 )

Type material. HOLOTYPE ♂, THAILAND: Satun Province, Langu District, Langu Subdistrict, Ban Pakbara (6°50’30.4”N 99°46’32.9”E), sweep netting, 29.IV.2015, A. Samoh leg., PSUNHM, PSUZCEN11 . PARATYPES. THAILAND: Satun Province, 3♂, 2♀, Langu District, Langu Subdistrict, Ban Pakbara (6°50’30.4”N 99°46’32.9”E), sweep netting, 29.IV.2015, A. Samoh leg., PSUNHM . Phang Nga Province, 1 ♂, 1 ♀, Thai Mueang district , Thai Mueang subdistrict, Ban Thap Pla , Mangrove creek and local fishing port (8°28’58.6”N, 98°15’17.5”E), sweep netting, 4.IV.2021, A. Samoh leg., PSUNHM. SINGAPORE: 1 ♂, Semakau Island ( SMO3 ) , 24.V.2012 ( ZRCBDP00002799 : barcoded, dissected and figured ( LKCNHM); 1 ♀, Semakau Island ( SMO3 ), 24.V.2012 ( ZRCBDP00007660 : barcoded; LKCNHM.

Other material examined. About 180 specimens of H. squamatus sp. nov. from Singapore have been NGSbarcoded and are all conserved at LKCNHM.

Diagnosis. The first flagellomere is elongated, three times as long as wide. All coxae and femora are black, with the exception of the tips of the fore and mid femora. The hind femur lacks long ventral setae at the base. Hind tibia with a very long ventral seta on apical third, being at least 3 times as long as tibia is deep. The male genitalia are notably long, extending to the thorax, and the cercus is triangular-shaped, equipped with seven strong, black bristles along the outer margin.

Description. Male ( Fig. 4 ). Small to medium species (body length 3.2–3.6 mm, wing length 3.2–3.5 mm). Head metallic green with pale grey pollen. Face narrowing downward, distinctly narrower than first flagellomere. Hairs and bristles black. Postocular bristles black. Antenna blackish brown, first flagellomere elongated, 3 times as long as wide; arista apicodorsal, minutely pubescent with basal segment 0.3 times as long as apical segment. Proboscis blackish brown with black hairs, palpus black with black hairs and black apical bristles. Thorax metallic green with pale grey pollen. Hairs and bristles black. Five strong dc, 6 pairs of acr; scutellum with 2 pairs of bristles (basal pair short and weak). Propleuron with 1 black bristle on lower part. Legs almost yellow; all coxae dark brown to black; femora also dark brown to black except tip of fore and mid femora. Mid and hind tarsi from tip of tarsomere 1 onward brownish. Hairs and bristles black. Mid and hind coxae each with 1 exterior bristle. Mid and hind femora each with 1 preapical bristle. Hind femur with 3 brown vs. near base (slightly shorter than width of femur). Fore tibia with 2 ad and 1 weak pd, apically with 3 long bristles, longest 0.8 times as long as tarsomere 1; mid tibia with 3 ad, 2 pd and 1 av, apically with 4 bristles; hind tibia with 3 ad, 3 pd and very long ventral on apical third, apically with 3 bristles. Fore tarsomere 1 with 2 vs.; hind tarsomere 1 with 1 vs at base. Wing hyaline, tinged with greyish; veins brown, R 4+5 and M 1+2 parallel apically, CuAx ratio 0.7. Squama yellow with black hairs. Halter pale yellow. Abdomen metallic green with pale grey pollen. Hairs and bristles black. Male genitalia long, reaching thorax. Epandrium about 3x as long as wide ( Fig. 6A ), ventral border of epandrium with narrow digitiform apicoventral epandrial lobe with 3 bristles ( Fig. 6A, B ). Cercus triangular with 7 strong, black bristles on outer margin ( Fig. 6D ).

Female ( Fig. 5 ). Body length 2.7–2.8 mm, wing length 2.4–2.5 mm. Similar to male, except first flagellomere as long as wide; hind femur without vs. at base and fore tibia without long apical ventral bristles.

Etymology. The specific epithet, squamatus refers to the numerous squamiform bristles on the apical border of the cercus.

Bionomics. This species was collected from shaded areas of mangrove creeks and back mangroves, which had an abundance of small pebbles, sand, and muddy soils in their vicinity.

Distribution. THAILAND: Phang Nga and Satun provinces ( Fig. 7 ), SINGAPORE: Pulau Semakau (Semakau Island).

Remarks. The newly discovered species bears a resemblance to H. brevidigitalis , particularly in the elongation of the first flagellomere, which is 3 times as long as wide. However, there are notable differences between the two species. In the new species, the hind femur lacks long ventral setae at the base. The hind tibia bears a very long ventral seta on apical third, being at least 3 times as long as tibia is deep. Furthermore, the cercus of the new species is triangular-shaped and characterised by the presence of seven robust, black squamiform bristles along its outer margin. In contrast, in H. brevidigitalis two long ventral setae are present at the base of the hind femur nearly as long as femur is deep, the hind tibia bears a much shorter ventral seta on the apical third that is about twice as long as tibia is deep and the cercus bears only three strong, black squamiform bristles on the outer margin ( Fig. 12 ). The genetic difference of H. squamatus sp. nov. and H. brevidigitalis is about 10%. The genetic distance of H. squamatus sp. nov. between South-Thailand and Singapore is between 1–2%, but no morphological differences have been distinguished.

Figures

FIGURE 4. Hercostomus squamatus sp. nov. Male habitus (photo: Abdulloh Samoh).

FIGURE 5. Hercostomus squamatus sp. nov. Female habitus (photo: Abdulloh Samoh).

FIGURE 6. Hercostomus squamatus sp. nov. Male terminalia (Singapore, Semakau, ZRCBDP00002799). A. Male terminalia lateral; B. ventral border of epandrium with apicoventral epandrial lobe; C. Tip of aedeagus and hypandrium; D. Lateral view of cercus and surstylus. Scale 0.1 mm (image P. Grootaert).

FIGURE 7. Distribution map of the mangrove associated species of Hercostomus in Thailand.

FIGURE 12. Hercostomus brevidigitalis Zhang, Yang & Grootaert, 2008. Male terminalia (Singapore, Pulau Ubin Ma10627). A. Tip of terminalia with cercus in lateral view; B. Apex of aedeagus and hypandrium in lateral view; C. Apicoventral lobe of epandrium; D. Cerci and surstyli in ventral view; E. Surstyli in lateral view. Scale 0.1 mm (image P. Grootaert).