Amblypsilopus Bigot, 1888

Bickel, Daniel J., 2019, The Amblypsilopus amnoni and megastoma groups in New Guinea (Diptera: Dolichopodidae: Sciapodinae), Israel Journal of Entomology (Oxford, England) 49 (2), pp. 195-214 : 197-200

Genus Amblypsilopus Bigot, 1888

Diagnosis: Head. Vertex distinctly excavated; head width almost always greater than height; row of short orbital setae and strong postvertical seta; strong diverging ocellar setae; male vertical seta usually weak and reduced, or absent; female vertical always strong; male face flat to only slightly bulging; male clypeus narrowed and distinctly free from eye margin in most species (MSSC); female clypeus almost always adjacent to sides of eyes; pedicel with short dorsal and ventral setae; first flagellomere usually subrectangular to subtriangular, sometimes modified in males; arista usually distinctly dorsal and arising near base of first flagellomere, although sometimes dorsoapical or apical; arista usually short, not much longer than head width; rarely with male apical flags or modifications.

Thorax. ac setae variable, from biseriate to absent; 4–5 pairs dc, almost always sexually dimorphic, in males two posterior dc (dc 1 and dc 2) always strong, and anterior dc variously reduced and hair-like (MSSC); in females, usually all dc setae strong, only slightly decreasing in size anteriorly; median scutellar setae strong, laterals always reduced to weak hairs or absent.

Legs. Often elongate and “delicate”; femora rarely with strong ventral setae; many characters diagnostic in defining species and species groups developed on legs, such as following MSSC: (a) tibiae and/or tarsomeres elongated or shortened, (b) tarsomeres I and II flattened, (c) IIIt 3–5 flattened and padlike, (d) tibiae and tarsi I and II with short erect or crocheted setae, (e) male TI or It 1 with pale curved posterior hairs.

Wing. Usually hyaline, but sometimes with apical maculations, vein M 1 usually with elbow-shaped bend, crossvein m–cu straight and usually forming right angle with vein M.

Abdomen. Relatively long in male; terga sometimes translucent yellow; hypopygial peduncle (segment 7) not greatly prolonged; hypandrium usually asymmetrical, with narrow left lateral arm, arising near base of hypandrium; phallus with dorsal angle; epandrial lobe with 2 strong apical bristles; surstylus and cercus various.

Remarks: Amblypsilopus is a rich and complex pan-tropical genus that acts as a “holding taxon” for many small and often delicate members of the Sciapodinae . The genus is not strongly defined and is possibly polyphyletic. However, Amblypsilopus can be split into good monophyletic species groups defined on male genitalic and secondary sexual characters, and thus provide the basic units or clades for systematic study. Amblypsilopus species are defined by a mosaic of male characters many of which are highly plastic in expression and lack evident polarities. The nomenclatorial history of Amblypsilopus is discussed in Bickel (1994).

Key to males of the Amblypsilopus amnoni and megastoma groups from New Guinea ( Diptera : Dolichopodidae : Sciapodinae ) 1 Vertex strongly excavated on either side of ocellar tubercle, or if weakly excavated, vein M distinctly branched, with M 2 present at least as a fold on membrane;

mesonotum short, about as wide as long; hypopygium exerted and distinctly pedunculate; posterior mesonotum never flattened (subfamily Sciapodinae ) ....2

– Vertex not excavated, vein M 2 usually absent; other characters various… ........................................................................................... other Dolichopodidae

2 Vein M unbranched but with gentle anterior bend beyond crossvein dm–cu (vein M 2 totally absent, without fold or indication on membrane); all dc and vertical seta present and strong in both sexes.................................... Mesorhaga Schiner

– Vein M branched and vein M 2 present, even if as fold on membrane; if unbranched, then males with anterior dc as weak hairs; other features various......................3

3 Arista dorsal or dorsoapical on subrectangular postpedicel; male tibial chaetotaxy often weak; crossvein dm–cu usually straight; vein M 2 usually straight, not arched; male vertical setae hairlike or absent, male clypeus narrowed and free from eye margin; male lateral scutellar setae hair-like or absent; body often appearing delicate, with elongate legs; male IIIt 3–5 rarely flattened and padlike ( Amblypsilopus Bigot ).........................................................................................................4

– Without most or all of above characters ......other Sciapodinae (not treated here)

4 Tibia I with single outstanding curved posterior seta, variously positioned, but usually along distal half, or if lacking long seta on tibia I, present on It 1 near joint with tibia; tibia on distal fifth to sixth slightly expanded with white ventral pile; male vertical seta usually reduced and weak; legs usually elongate and yellow; abdominal segments sometimes partially translucent yellow.............................5

– Tibia I without outstanding posterior seta, or with series of short posterior setae; other features various...............................other Amblypsilopus (not treated here)

5 Labella of both sexes greatly enlarged ( Figs 20, 22); both sexes with basitarsus I longer than tibia I; tibia I with short pale curved posterior seta at 9/ 10, just before apex (It 5 black, flattened and expanded into apical pinnate flag; cercus long and flagellate ( megastoma Group).............................................................................6

– Labella unmodified, not enlarged; other characters various...............................7

6 Clypeus pale yellow; enlarged labella trapezoidal; wing length <4.8 mm; scutellum dorsally dark blue but with yellow dorsal rim; hypopygium basally yellow and distally dark brown ( Figs 18–21). (<1000 m)................ A. megastoma n. sp.

– Clypeus yellow with green reflections; labella elongate, blade-like; wing length> 5.2 mm; scutellum dorsally entirely blue-green; hypopygium entirely dark brown ( Figs 22–24). (> 2000 m)............................................................... A. ialibu n. sp.

7 SUrstylUs elongate digitiform and cUrved, at least ⅓ length of epandriUm; base of basitarsus III near join with tibia III with 2 short ventral setae ( amnoni Group)8

– Surstylus short, less than ¼ length of epandrium; basitarsus III various..............

...other Amblypsilopus with posterior cUrved seta on ♂ tibia I (not treated here)

8 Cercus rather thick and setose with ventral recurved arm; basitarsus I longer than tibia I; leg I tarsomere 5 without apical tarsal flag.............................................9

– CercUs elongate, digitiform and cUrved, basitarsUs I variable; leg I tarsomere 5 modified into flattened black flag...................................................................10

9 Thorax metallic blUe-green; tibia I slightly bowed, and slightly flattened with whitish ventral pile along length; basitarsus I ventrally bare; sternite 8 yellow; hypopygium almost entirely yellow with basal hypandrium infuscated; surstylus curved, digitiform about half length of epandrium; cercus basally swollen, with distal cercus digitiform arm recurved against base ( Figs 14, 15). (> 2000 m).... .............................................................................................. A. ibiscorum n. sp.

– Thorax almost entirely yellow; tibia I ventrally bare; basitarsUs I with groUp of 3 black ventral setae at very base (MSSC); sternite 8 dark brown; hypopygium dark brown with yellow surstylus and cercus; cercus with blade-like ventral arm arising near ⅖ and recUrved back towards cercal base, and distally tapering with long hairs ( Figs 16, 17)............................................................ A. riuensis n. sp.

10 Cercus distinctly branched into two or more distinct arms.............................11

– CercUs with single elongate Unbranched arm or with short projection...........12

11 Basitarsus I shorter than tibia I; tibia I slightly bowed, with ventral surface of distal third ivory colored; leg I tarsomere 4 slightly flattened with ivory colored pruinosity, and leg I tarsomere 5 black and expanded into apical pinnate flag; wing hyaline; hypopygium mostly dark brown; cercus in broad C-shape with setose dorsal arm and curved bladelike medially directed ventral arm ( Figs 9–12)..... .................................................................................................... A. kaindi n. sp.

– BasitarsUs I longer than tibia I; leg I tarsomere 5 slightly flattened; wing with brownish infuscation on distal quarter; hypopygium mostly yellow; cercus with basal triangular projection from which elongate arm diverges at right angles ( Fig. 13) ...................................................................... A. pulverulentus (Parent)

12 Thorax mostly yellow; hypopygium yellow; surstylus curved, elongate, almost twice as long as epandrium; cercus basally swollen, becoming elongate and extended, flagelliform and curled, almost 3× as long as epandrium ( Figs 5–8) .................................................................................................... A. okapa n. sp.

– Thorax mostly metallic green-blUe; hypopygiUm color varioUs; sUrstylUs cUrved, elongate, shorter than epandrium; cercus subequal to or shorter than epandrium ........................................................................................................................13

13 Basitarsus I subequal to TI; leg I tarsomere 5 black, flattened and expanded into apical pinnate flag; hypopygium basally yellow but distally brown, cercus short, digitiform, only slightly swollen basally, and unbranched with pale yellow hairs ( Figs 1, 2)........................................................................................... A. amnoni

– BasitarsUs I UnUsUally long and bowed, more than twice length of tibia I; leg I tarsomere 4 flattened into three bright ivory colored surfaces; leg I tarsomere 5 black, flattened and expanded into large apical pinnate flag; hypopygium dark brown; cercus swollen basally, on point like extension of epandrium, and elongate with two digitiform arms ( Figs 3, 4)......................................... A. pascali n. sp.

The Amblypsilopus amnoni group

Diagnosis: Head. Major head setae often yellow on both sexes; vertical seta on lateral frons slightly shorter than postvertical; first flagellomere short, rounded subtriangular; arista dorsal, and as long as head height.

Thorax. Two pairs of long ac present, with shorter pair anteriormost; two strong posterior dc and weak hair-like dc anteriad in males, and also in known females; median scutellar setae strong, laterals absent.

Legs. Coxa I yellow; coxae II and III brown, at least basally and remainder of legs mostly yellow; tibia I with single long curved posterior seta variously positioned, but usually along distal half (sometimes with additional weaker setae distad); TI on distal fifth to sixth slightly expanded with white ventral pile; TII with anterior seta at ⅘, and UsUally withoUt ad setae.

Abdomen. Segment 7 (hypopygial peduncle) elongate with tergum 7 much longer than sternum 7 ( Fig. 1a); epandrium subtriangular to subrectangular; surstylus distally narrowed and curved, elongate, hypandrium with smooth ventral surface; phallus without subapical barb-like projection; cercus various.

Remarks: Almost all species of the Amblypsilopus amnoni group are known from montane rainforest of Papua New Guinea, at elevations mostly above 1500 m. The only exception is A. riuensis from 250–300 m on low-lying Sudest Island in Milne Bay Province.

Species of the amnoni group are readily recognized by the curved digitiform surstylus, often as long as or longer than the epandrium (e.g., Figs 2, 7, 13, 15). Also, known females of the amnoni group have some anterior dorsocentral setae reduced to fine hairs, normally a character only found as a male secondary sexual character in Sciapodinae . This is another example in the Sciapodinae where an otherwise male secondary sexual character has been incorporated into the female phenotype (see Bickel 1994). Other characters of note in both sexes of the amnoni group are the pair of short ventral setae near base of basitarsus III and the antennal pedicel with a strong dorsal seta, but without a corresponding ventral seta.

Seven species from the amnoni group, all from Papua New Guinea, are treated below: amnoni n. sp., ibiscorum n. sp., kaindi n. sp., okapa n. sp., pascali n. sp., pulverulentus (Parent) , riuensis n. sp.

I have seen damaged specimens of another species from West Sepik Province, Green River that belongs in the amnoni group (BPBM).