Stenopygium Becker

SCOTT E. BROOKS, 2005, Systematics and phylogeny of Dolichopodinae (Diptera: Dolichopodidae), Zootaxa 857, pp. 1-158 : 109-112

Genus Stenopygium Becker

( Figs. 28 A–C, 29A–E)

Stenopygium Becker, 1922a: 75 . Type species: Stenopygium nubeculum Becker [Neotropical], by monotypy.

New Combination. The following new combination is proposed: Stenopygium punctipennis ( Say, 1829) comb. nov. ( Pelastoneurus ).

Recognition. Stenopygium can be recognized by the following combination of characters: clypeus bulging and subequal in height to face, arista usually pubescent (occasionally plumose in females), 6 dorsocentrals, wing with brownish spots or bands, vein M beyond crossvein dm­cu with weak anterior bend before middle, hypopygium distinctive, subtriangular, phallus strongly wrinkled. Stenopygium is similar to Pelastoneurus and Platyopsis and can be distinguished from these genera by the characters given above and in the key.

Description. Head: Vertex more or less flat to weakly excavated, 1 pair of strong vertical setae, stronger than postverticals. Frons about 3– 4 x wider than high, sides slightly convergent anteriorly. Face and clypeus broad, broader in female; face with sides subparallel to weakly converging below; clypeus strongly bulging and subequal in height to face, widening below, lower margin straight, not reaching lower eye margin. Palp large, subtriangular with weak setae on outer surface and a weakly differentiated to distinct apical seta. Proboscis large and thick. Antenna: Scape short, subconical, with well­developed acute medioventral process; pedicel short; first flagellomere subrectangular to subtriangular, weakly to strongly pointed dorsoapically, longer than high in male, about as long as high in female; arista dorsal, close to base in male, 2­segmented, distal segment strongly pubescent, occasionally plumose in females (e.g., S. punctipennis ). Postvertical setae slightly to distinctly stronger than uppermost pair of postoculars.

Thorax: Acrostichals biserial; 6 dorsocentrals, aligned or with fifth pair weakly offset medially; 1 outer posthumeral, 1 weaker inner posthumeral; 2 notopleurals; 1 presutural; 1 sutural; 2 supraalars; 1 postalar. Upper and lower part of propleuron with weak hairs; lower part of propleuron with 1 strong prothoracic seta; pleural surface in front of posterior spiracle bare; metepisternum with a row of fine hairs. Scutellum with 1 strong inner seta and 1 small outer seta on lateral margin.

Legs: Pulvilli developed normally on all legs. Foreleg: Basitarsus with distinct basiventral seta. Midleg: Femur with 1 anterior preapical seta, S. nubeculum with a series of long, fine hairs basiventrally; basitarsus with weak to distinct basiventral seta. Hindleg: Coxa with strong lateral seta slightly to distinctly below middle; femur with 1 anterior to anterodorsal preapical seta, sometimes with 1 weak anteroventral preapical seta; tibia of male without posteroapical process; basitarsus distinctly shorter than second tarsomere, usually with distinct basiventral seta and 1–2 weaker ventral setae, male with well­developed dentiform to hook­like process posterobasally.

Wing: Grayish with several distinct to weakly defined dark spots or bands. R2+3 relatively straight to weakly curved; R4+5 curved posteriorly in distal section; distal section of M beyond crossvein dm­cu with weak anterior bend before middle, convergent with R4+5, ending before wing apex; crossvein dm­cu subequal to or longer than distal section of CuA1.

Abdomen: Subconical. Male: T6 bare; S2–S3 unmodified; S4 emarginate and membranous posteromedially; S5 sclerotized along anterolateral margin, mainly membranous posteromedially; S6 mainly membranous, weakly sclerotized along anterior margin; segment 7 forming well­developed peduncle; S8 subrectangular, narrowed basally, setose. Hypopygium ( Figs. 28 A–C, 29A–C): Epandrium subtriangular in lateral view, about 2.0– 2.4 x longer than high; foramen positioned anterolaterally, well­separated from base of cerci; basiventral epandrial lobe not developed, basiventral seta positioned before middle of ventral epandrial margin; apicoventral epandrial lobe weakly developed, ridge­like, bearing 2 setae. Surstylus bilobed. Ventral lobe digitiform to subtriangular with broadened base, 1 lateral seta, 1–2 strong apical setae. Dorsal lobe digitiform with 2 strong apical setae. Postgonite with anteroventral portion well­sclerotized, with trough­like base positioned below sperm pump; posterodorsal portion well­developed, digitiform. Proctiger brushes present. Cercus subtriangular, narrow and elongate in S. nubeculum ( Fig. 28 A). Hypandrium long, symmetrical, membranously connected to epandrium basiventrally, free laterally, with rounded preapical lobes laterally, apex weakly emarginate ( Fig. 28 C) or bifurcate ( Fig. 29 C); hypandrial apodeme absent; hypandrial arms connected to hypandrium. Sperm pump subcylindrical; ejaculatory apodeme variable, rod­like to distinctly flattened laterally, apex sometimes medially split; basal sclerite of sperm pump V­shaped to nearly straight in dorsal view. Phallus long and slender, elbowed at base, middle section strongly wrinkled ( Figs. 28 B, 29A,B). Female ( Fig. 29 D,E): T6, S6 and S7 undivided, T7 weakly divided medially; T8 and S8 divided medially, tergite and sternite fused anterolaterally forming a narrow sclerite ( Fig. 29 E). T10 divided medially into hemitergites each bearing 5 spines.

Geographical Distribution. Stenopygium is known from Mexico, Costa Rica and Bolivia.

Phylogenetic Relationships. This genus appears to be closely related to Pelastoneurus ; however, the precise relationships between Stenopygium , Pelastoneurus and Platyopsis is currently unclear.

Remarks. Becker (1992a) originally erected this genus based on the possession of a ventral indentation on the first flagellomere of males and an elongate male cercus. However, both of these features are autapomorphies of S. nubeculum , and the former character is not always as distinct as indicated in Becker’s figure.

Material Examined. Stenopygium nubeculum Becker , [NT]: 3ɗ syntypes ( SMTD); Stenopygium punctipennis (Say) , [NT]: 7ɗ, 4Ψ ( USNM); 1ɗ ( CAS); 1ɗ ( CNC).

Figures

FIGURE 28. Stenopygium nubeculum: (A) Male genitalia, left lateral view (external); (B) Male genitalia, left lateral view (internal); (C) Male genitalia, ventral view (postgonite, surstylus and cerci not shown).

FIGURE 29. Stenopygium punctipennis: (A) Male genitalia, left lateral view (external); (B) Male genitalia, left lateral view (internal); (C) Male genitalia, ventral view (postgonite, surstylus and cerci not shown); (D) Female genitalia, dorsal view; (E) Female genitalia, left lateral view.