Erebomyia Runyon & Hurley

Hurley, Richard L. & Runyon, Justin B., 2009, A review of Erebomyia (Diptera: Dolichopodidae), with descriptions of three new species, Zootaxa 2054, pp. 38-48 : 39-41

Genus Erebomyia Runyon & Hurley

Erebomyia Runyon & Hurley, 2004 : S114. Type species: Erebomyia exalloptera Runyon & Hurley, 2004 , by monotypy.

Diagnosis. Body length 3.0– 4.5 mm. Vertex of head not excavate. Antennal scape without dorsal setae; pedicel without medioapical thumb-like projection. Wing with costa continuous to tip of unbranched vein M; crossvein dm-cu shorter than last part of CuA1. Thorax with postpronotal hairs ( Fig. 2 ; see Remarks); 6 dc setae; posterior scutum not distinctly flattened; notopleuron with 2 setae; proepisternum with only a few hairs. Femur II and III with preapical seta. Hypopygium forming a cap to abdomen. Males: wings modified in shape, with hairs near apex ( Figs. 1 , 3–5 ). Left hypandrial arm large, hooked; right hypandrial arm short ( Figs. 6–8 ).

Description. Males: Head: without lower postcranial hairs (beard) or gena. Face short, not reaching ventral margin of eyes; very narrow to obliterated near middle by encroaching eyes. Postocular setae white, with dorsal 5–7 usually yellow-brown to brown, becoming slightly longer and more slender ventrally. Ocellar and outer vertical setae long. Scape and pedicel mostly yellow; first flagellomere triangular, brown. Arista basal, hispid; with somewhat thickened basal aristomere. Thorax: 6 long dc; ac in a single row. Postpronotal hairs present ( Fig. 2 ; see Diagnosis of genus). Scutellum with one pair of long setae, without hairs. Proepimeron bare. Notopleuron with 2 long setae. Halter yellow. Calypter yellow, black at apex; with fan of long yellow setae. Legs: including coxa, long and slender, yellow, with distal tarsomeres often brownish. Anterior surface of coxa I with white hairs and yellow-brown to brown setae at apex. Coxa II and III with long, slender, dorsal seta near 1/2. Tibia I without distinct setae. Femur II and III with preapical anterior seta; with av seta near apex. Wing: male wings variously modified, but all with slender, very short to long marginal hairs near apex ( Figs. 1 , 3–5 ). Abdomen: cylindrical; dark brown, with some yellow near base. T1 with very long, slender setae along posterior edge, lateral setae longest and often yellowish, medial setae shorter and darker. Hypopygium ( Figs. 6–8 ) small, mostly embedded; epandrium longer than wide, without distinct lobes. Surstylus with ventral lobe larger than dorsal lobe; dorsal lobe narrow, digitiform, with one lateral seta before apex; ventral lobe much broader, with 3–4 apical setae and subapical digitiform lobe bearing one seta at apex. Postgonites present as a pair of tubular sclerites, extending around base of phallus and looping ventrally then dorsally to weakly fuse with ventral surface of a small sclerite ventroapical of sperm pump, and branching laterally to fuse with base of bacilliform sclerites. Cerci short, narrow, pale brown with yellow setae and hairs, with 2–3 very long pale yellow setae at apex. Hypandrium ( Fig. 6 ) asymmetrical, arrowhead-shaped ventrally, extending dorsally near base on each side, then arising as hooked arms extending apically which fuse basally with bacilliform sclerites; right apical hypandrial arm short; left hypandrial arm very large, hooked to the left, with microtrichia covering apex.

Females: Similar in appearance to Sympycnus and Calyxochaetus ; can be recognized by postpronotal hairs. Similar to males but: face broader, only slightly narrowed below (width subequal to width of first flagellomere); palpus broader; first flagellomere short triangular, a little wider than long; scape and pedicel often with some brown dorsally; wings unmodified.

Remarks: Erebomyia belongs to the subfamily Sympycninae , a diverse cosmopolitan taxon containing many genera and species. Although its position within the subfamily is unclear, Erebomyia appears to be monophyletic based on the presence of postpronotal hairs ( Fig. 2 ), development of the left hypandrial arm into a large hook, modified wings in males, and perhaps habitat specialization - occurring only on deeply shaded vertical or overhanging, bare rock. The paucity of specimens in collections (we have searched most of the major collections in North America) is surprising given their occurrence, often in large numbers, in wellcollected areas, e.g., Madera Canyon and Cave Creek Canyon in Arizona. Increased attention to the microhabitats in which Erebomyia occur (dark rock cavities near streams) particularly in southwestern U.S.A. and Sonora Mexico, should provide additional species.

Postpronotal hairs, though sometimes difficult to see, appear to be a synapomorphy separating Erebomyia from other Nearctic Sympycninae and perhaps other Dolichopodidae in general. They are a cluster of very short, pale hairs found on the extreme anterior slope of the scutum in line with the dc setae ( Fig 2 ).

Males are easily identified to species using wing characters. Determination of females is difficult since, unfortunately, the distinct wing modifications of males are not reflected in females. Females of E. ramseyensis can be distinguished by the relatively short anterior preapical seta on femur III. Subtle differences appear to exist among the other species as noted in descriptions, but we cannot find reliable diagnostic features to allow confident identification of isolated females.

Figures

FIGURE 1. Erebomyia exalloptera, overlay of left (larger wing, on top) and right wings of male.

FIGURE 2. Erebomyia exalloptera, left lateral view. Arrow indicates left postpronotal hairs on anterior slope of scutum.

FIGURES 3 – 5. Erebomyia, male wings. 3. E. akidoptera; 4. E. aetheoptera; 5. E. ramseyensis. Note: in wing of E. aetheoptera, the anterodistal and posterobasal margins are slightly bent forward (toward reader).

FIGURES 6 – 8. Erebomyia genitalia. 6. E. exalloptera, ventral view; 7. E. exalloptera, left lateral view; 8. E. ramseyensis, left lateral view. Abbreviations: bac scl—bacilliform sclerite, cerc—cercus, dsur—dorsal lobe of surstylus, ej apod—ejaculatory apodeme, epand — epandrium, hypd—hypandrium, hypd arm—hypandrial arm, pgt—postgonite, ph—phallus, S 8 — sternite 8, vsur—ventral lobe of surstylus.