Hemichaeta Steyskal 1968

Marshall, Stephen A. & Jackson, Morgan D., 2014, A redefinition of the genus Hemichaeta Steyskal, new status (Diptera; Micropezidae; Taeniapterinae), Zootaxa 3815 (2), pp. 291-296 : 292-293

Hemichaeta Steyskal 1968

Hemicheta Hennig, 1934: 104 (as subgenus of Poecilomyia Hennig 1934: 96 ). Nomen nudum; genus-group name proposed after 1930 without designation of type species from four included species (ICZN (1999) - Art. 67.4.1). Hemichaeta Steyskal, 1968: 11 , as subgenus of Poecilotylus Hennig, 1934 . Type species: Grallomyia scutellata Cresson, 1930 (original designation).

Notes: As pointed out by Evenhuis et al. (2008), Hemicheta Hennig 1934 is a nomen nudum. Spelling, authorship, and date are from Steyskal (1968), who fulfilled the criteria for availability by designating a type and citing Hennig (1934: 97) for generic characters.

Diagnosis. Hemichaeta scutellata , the only species in the genus, is easily recognized by its compact appearance, small size (body length, excluding wings, approximately 6mm), short abdomen, stout distal anteroventral bristles on the hind femur, fusion of R4+5 and M1+2 prior to the wing tip, and a relatively short and broad anal cell. The flat to slightly depressed frontal vitta, general pigmentation, and single large frontal bristle are also useful diagnostic features, although similar characters occur in other genera.

Description (genus and species): Small, compact flies with the thorax distinctly higher than long and the abdomen unusually short, subequal to the combined length of the head and thorax. Length from head to abdomen tip (excluding deflexed oviscape) 6mm. Colour (see Figs. 1–4 ): head dark red dorsally, frontal vitta velvety black, lower frons and face red to orange, parafacial and gena silvery pruinose, palpus black with a contrasting yellow apex; thorax black with extensive silver pruinosity including four large silver notal patches dorsally, legs mostly pale brown except black fore tibia and tarsus and bands as described below; abdomen brown.

Head (Figs. 3,4): Postocellar, outer vertical and inner vertical bristles strong, orbital bristle and fronto-orbital bristle subequal; orbital bristle at level of ocelli, front bristle at edge of midpoint of the circular, flat to slightly depressed, velvety black frontal vitta. Preocellar frontal vitta slightly longer than wide, not reaching ptilinal suture, rounded on anterior margin. Frontal vitta strongly tomentose surrounding ocellar triangle, slightly depressed and strongly contrasting against shining epicephala. Lower fifth and lateral edges of frons red to orange, elevated laterally. Eye margined by a narrow silvery strip continuous with parafacial strips. Lunule subequal in width to scape and continuous with the elevated, flat-topped, parallel-sided midfacial ridge. Clypeus small, narrow, microsetulose and dark. Palpus broadly oval, almost parallel sided (unlike the ventrally convex palpus, characteristic of related Taeniaptera Macquart s.l.). Antenna short, scape and pedicel with only minute setulae, first flagellomere oblong, 1.3X as long as wide; arista short, bare except for some minute setulae near base, length 2.7X length of first flagellomere.

Thorax: Prothorax distinct, collar-like but short, shiny. Cervical sclerite rounded, strongly convex and domelike posteriorly. Mesothorax distinctly higher than long, with 2 equal notopleural bristles, large supralar and postalar bristles, 1 large prescutellar dorsocentral bristle and 1 large apical scutellar bristle. Scutellum densely microtrichose (not setulose), especially along margins, velvety black in contrast with the dull black scutum marked with large dorsal silvery patches of tomentum; subscutellum whitish microtrichose. Katepisternal bristles golden brown. Katatergite convex, elongate dome-like, withish microsetulose centrally.

Legs: All femora and tibiae cylindrical, without distinct sulci. Fore femur and fore coxa cream yellow, except for a broad preapical brown band on femur; fore tibia and tarsus dark brown to black; distal 3/4 of fore femur with dense short golden setulae and no larger bristles. Mid and hind femur banded in brown and yellowish-brown ( Fig. 1 ), with a distinctive broad cream yellow distal band margined by narrow dark brown bands. Apex of mid and hind femora and all of mid and hind tibiae brown. Mid tibia with anterodorsal row of short stout bristles, hind femur with anterodorsal and posterodorsal rows of the same bristles. Hind femur slightly swollen distally, with 2–3 stout anteroventral preapical bristles ( Fig. 3 ).

Wing ( Fig. 4 ): Slightly infuscated over entire surface, no transverse banding or dark pigmented markings. Wing microtrichose, except for bare basal third of cell br, entirety of cells bm and cu p, and small oval near junction of A2 and A 1 in anal cell. Anal cell short and broad. A1+CuA2 roughly two-thirds length of CuA2, cell cu p longer than broad; A1+CuA2 weakened but attaining wing margin, curved slightly towards wing base at midpoint. R4+5 and M1+2 fused prior to the wing tip (cell r4+5 closed); R4+5+M1+2 slightly shorter than crossvein r-m, costa ending where R4+5+M1+2 meets the wing margin. CuA1 beyond dm-cu, subequal to dm-cu.

Female abdomen: Oviscape broad basally, tapering apically, almost as long as rest of abdomen, shiny reddishbrown without the pruinosity covering the rest of the abdomen. Ventral receptacle short and broad. Common spermathecal duct broad and convoluted prior to dividing into narrow bases of individual spermathecal ducts, both ducts abruptly widening just beyond base; single duct parallel sided until spermathecal stem which is narrower than duct at base and gradually swells to an irregularly oval spermatheca with several processes. Paired spermathecal duct broadest near base, narrowed at spermathecal stem. Spermathecal stem strongly sinuate-coiled and expanding to elongate oval, striate spermathecae with distinct process on basal half ( Fig. 7 ).

Male abdomen: Genital fork (sternite 5) with two long incurved arms, each with 4–6 stout inner bristles, base between arms very broad, narrowly cleft medially ( Fig. 6 ). Anterior part of sternite 5 as long as arms, with a differentiated pale patch of minute setulae anteromedially. Epandrium reddish brown, laterally shining, dorsally microsetulose, subequal in length and height; cerci large and densely setose. Hypandrium elongate, Y-shaped with a loop-like posterodorsal bridge connecting to aedeagal guide on each side; posteriorly articulating with extended anteroventral corner of epandrium. Distiphallus long and mostly parallel-sided, ending in a slightly swollen phallic bulb and then an elongate, tapered distal process. Ejaculatory apodeme large, with a flanged apodeme and a helmet-like sperm pump. Phallapodeme narrow, elongate. Postgonite with a finely microspinulose, rounded apex, with 2–3 minute preapical ventral bristles ( Fig. 5 ).

Type material. Holotype male ( USNM #27885) and two paratype females: PANAMA, Canal Zone, February 6, 1911, A. Busck.

Other material examined. COSTA RICA. Prov. Puntarenas, 2km N Dominical, Hacienda Baru ecolodge, 22–25.Feb.2006, S.A. Marshall (7 ♂, 1♀, INBC, DEBU); Heredia, La Selva Biological Station, Puerto Viejo, main trail STR, 9–10.Feb.2003, M. Pollet (1♂, DEBU). VENEZUELA. Sucre, Puy-Puy, 32kmE Carupano, plantations and secondary forest near beach, sweep, 31.Mar–2.Apr, 1988, M. von Tschirnhaus (4♂, 1♀, DEBU).

Biology. What little is known about the biology of Hemichaeta is reflected in the label data and Figs. 1 and 2 . Figure 2 shows a mating pair with the female oviscape directed upwards and held in position by the male's genital fork. The male's forelegs sit on the female's thorax, with his tarsi on the female's swollen cervical sclerites. Some other micropezid genera, for example Plocoscelus Enderlein , Taeniaptera and Scipopus Enderlein engage in complex precopulatory behavior including "kissing" and "stroking", but no such behaviour has been noted in Hemichaeta . Most of the Costa Rican specimens were taken on low (30–40cm) vegetation near sea level on the Pacific coast, and most were males apparently "displaying" on the leaf surfaces with the forelegs extended straight out in front of the body ( Fig. 1 ).

Relationships. Poecilotylus is an artificial assemblage of Taeniapterini (sensu Aczél, 1951) that lack the characteristically axe-shaped palpus diagnostic for the lineage including Taeniaptera and related genera. There are no synapomorphies linking Hemichaeta to Poecilotylus , but both morphological and molecular characters suggest that Hemichaeta is instead part of a clade including Taeniaptera and related genera, and excluding other " Poecilotylus ". Taeniaptera s.l. have preapical bristles on the hind femur similar to, albeit smaller than, the short, stout anterior preapical bristles of Hemichaeta . Both Hemichaeta and Taeniaptera s.s. have a similar and probably derived distiphallus, which extends beyond the phallic bulb as a characteristically long and dorsally recurved portion. Further evidence that Hemichaeta is more closely related to Taeniaptera than Poecilotylus comes from a recent molecular phylogeny of Taeniaptera Macquart and some related Taeniapterinae (Jackson et al., in prep). Analysis of two mitochondrial genes (12S and COI) and two nuclear genes ( CAD and wingless) places Hemichaeta scutellata distant from other " Poecilotylus " but as sister group to a clade including Taeniaptera s.s. and Grallomyia Rondani. These data suggest that it is necessary to either include Hemichaeta in a very broadly defined Taeniaptera or recognize it as a separate genus; it can no longer be treated as a subgenus of Poecilotylus .

Figures

FIGURES 1 – 2. Hemichaeta scutellata (Cresson), Hacienda Baru, Costa Rica, 2008. 1, male displaying on leaf surface; 2, mating pair.

FIGURES 3 – 7. Hemichaeta scutellata (Cresson). 3, male lateral showing wing venation and hind femur apical setae, with inset showing maxillary palpus; 4, male head (abbr: fr s, frontal seta; i vt s, inner vertical seta; orb s, orbital seta; o vt s, outer vertical seta; poc s, postocellar seta); 5, male terminalia; 6, male sternite 5 with genital fork; 7, female spermathecae and associated structures.