Chersodromia nigripennis, Shamshev, Igor & Grootaert, Patrick, 2005

Shamshev, Igor & Grootaert, Patrick, 2005, Two new species of the genus Chersodromia Walker (Diptera: Hybotidae) from Southeast Asia, Zootaxa 942, pp. 1-10 : 3-6

Chersodromia nigripennis new species

Fig. 1

Diagnosis. A small species with 2 pairs of vertical bristles, very narrow face, black antennae, conical postpedicel, wholly pollinose katepisternum, brownish palpus, halteres and legs and usually deeply infuscate wings.

Description. Male. Body length 1.7–1.9 mm, wing length 1.6–1.7 mm. Head black in ground­colour, with black bristles. Frons greyish pollinose, rather narrow, somewhat widened towards ocellar tubercle, in middle nearly 1.5 times as broad as anterior ocellus. Face almost linear, widened in lower part, narrow, in middle nearly 3.0 times narrower than frons. Ocellar tubercle and vertex with 2 pairs of long bristles. Occiput greyish pollinose, with some scattered setulae longer in lower part. Antennae ( Fig. 1 A) black, with postpedicel conical, about 3 times longer than wide, style nearly 2 times as long as postpedicel. Genae rather narrow. Palpus ( Fig. 1 B) moderately large, brownish, elongate oval, with several short bristles; sensory pit present.

Thorax black in ground­colour, wholly densely greyish pollinose, including katepisternum, with black bristles. Postpronotal bristle long, inclinate. Mesonotal bristles well prominent, presutural supra­alar lacking, 3 notopleurals (2 longer), 1 postalar and 4 (inner ones cruciate) scutellars. Acrostichals irregularly uniserial, short, scattered, 2 long, paired bristles on prescutellar depression. Dorsocentrals uniserial, long, about 4 per row, lacking on prescutellar depression, some setulae present on supra­alar space.

Legs almost wholly brownish, only fore femur at apex and fore tibia at extreme base brownish yellow (in paler specimens also coxae at apex, trochanters and tarsi paler). Femora subequal in thickness. Fore tibia rather spindle­like, narrowed at base. Coxae and trochanters with ordinary setation. Fore femur with 1 row of antero­ and 1 row of posteroventral moderately long bristles, bearing 1 longer anterior subapical bristle and some bristles around tip. Fore tibia bearing 1 long anteroventral and 1 similar posteroventral bristle in subapical part, with some erect dorsal setulae. Fore tarsus somewhat dilated, nearly as long as fore tibia, tarsomere 1 with 1 long and 1­2 shorter posteroventral bristles. Mid femur with 1 row of posteroventral, moderately long (becoming shorter toward apex of femur) bristles in basal part, 2 long, thin bristles at extreme base and 1 anterior subapical bristle. Mid tibia with 1 row of anteroventral spinules, 2 long anterodorsal bristles in middle part and circlet of 3 subapical bristles. Mid tarsus somewhat dilated, nearly as long as mid tibia. Hind femur with 1 row of short (2 subapicals longer) posteroventral bristles, 1 row of short posterodorsal bristles and some prominent dorsal bristles near base. Hind tibia with 2 long anterodorsal, 3 similar dorsal and 2 anteroventral bristles, bearing 2 shorter subapical bristles anteriorly and longer ventral setulae. Hind tarsus slender. Otherwise legs clothed in ordinary setulae.

Wing normally developed, usually deeply infuscate (sometimes paler grey), covered with uniform microtrichia. Costal vein with moderately long setulae along anterior margin. One long basicostal bristle present. Vein R1 meeting costa at middle of wing. Veins R4+5 and M1+2 parallel and straight in apical part. Vein A1 present, very fine, fold­like. Halter with brown knob and pale stem. Squamae brownish, with scattered brownish fringes.

Abdominal sclerites mostly pale brown and with scattered dark setulae, pregenital segments darker and with longer bristles. Intersegmental gland­like structures or squamiform setae absent.

Hypopygium ( Fig. 1 C) moderately large, black. Hypandrium with 7 long bristles in apical part. Epandrium completely divided. Left epandrial lamella small, fused to hypandrium, with several short bristles in apical part. Left surstylus ( Fig. 1 D) consisting of two entirely separated sclerites; upper sclerite rather elongate oval, with 1 spine at apex; lower sclerite digitiform, with additional processes in basal part and near middle. Right epandrial lamella subrectangular ( Fig. 1 E), clothed in numerous bristles, with small apical lobe bearing 1 long and 1 short spine. Right surstylus not prominent. Both cerci unbranched, bearing several long bristles, lacking spines, rather short; left cercus nearly 2.0 times broader and 1.5 times longer. Hypoproct unmodified. Phallus short.

Female. Body length 1.8–1.9 mm, wing length 1.7–1.8 mm. Resembling male in all respects except for sexual differences. Cerci brown.

Distribution. Singapore.

Derivatio nominis. The name refers to the quite dark wings.

HOLOTYPE. Male, SINGAPORE, Sungei Buloh, 27.XI. 2003, mangrove (sample 23090, leg. P. Grootaert), dry mounted on pin (in coll. RBINS).

PARATYPES. 1 males, 10 females, Singapore, Sungei Buloh, 27.XI.2003, mangrove (sample 23090, leg. P. Grootaert; in Raffles Museum); 14 males, 3 females, Singapore, Pulau Ubin, 11.XII.2002, beach in front of mangrove (sample 22061, leg. P. Grootaert); 18 males, 5 females, Singapore, Pulau Ubin, 11.XII.2002, beach in front of mangrove (sample 22059, leg. P. Grootaert); 1 female, Singapore, Sungei Buloh Nature Reserve, 9.XII.2002, in mangrove (sample 22057, leg. P. Grootaert); 7 males, 2 females, 28.III.2005, mangrove (sample 25037, leg. P. Grootaert); 1 male, 2 females, Singapore, Pasir Ris, mangrove, 4.XII.2003, (sample 23106, leg. P. Grootaert); 2 males, 4 females, Singapore, Pulau Ubin, Chek Jawa, 2.XII.2003, Malaise trap in mangrove (sample 23097, leg. P. Grootaert); 2 males, 2 females, Singapore, Chek Jawa, 19.XI.2003, sweep netting in mangrove (sample 23080, leg. P. Grootaert); 4 males, Chek Jawa, 26.III.2005, beach (sample 25031, leg. P. Grootaert).

Bionomics. This species was found on beaches in front of mangroves. The soil was black mud intermingled with small sandy patches. There was some variation in the darkening of the wings. A few specimens had rather pale wings. We suppose that the dark wings are a local homochromatic adaptation as a camouflage on a black background. The paler specimens might have an advantage on the white sandy patches.

Remarks. The new species somewhat resembles the Palaearctic C. cursitans (Zetterstedt) and C. hackmani Chvála differing primarily from the former by the lack of a presutural supra­alar (= posthumeral) bristle and by the slightly dilated fore tarsomeres and from the latter by longer bristles on the body and by the conical postpedicel. Also, the new species can be readily distinguished from the species known from Papua New Guinea ( Grootaert, 1992) in brownish palpi and halteres. Chersodromia nigripennis sp. nov. appears to belong to the C. incana group sharing with the species included there the very narrow face, entirely pollinose katepisternum and similar structure of the male terminalia. Although, within the key given by Chvála (1977) C. nigripennis sp. nov. would run to the couple joining the species of the C. cursitans group.

Figures

FIGURE 1. Male Chersodromia nigripennis sp. n., A, lateral view of antenna; B, dorsal view of palpus; C, ventral view of hypopygium; D, right lateral view of left surstylus; E, left lateral view of right epandrial lamella. Scale 0.1 mm.