Mesorhaga, Schiner

Bickel, Daniel J., 2007, The Mesoamerican Mesorhaga (Diptera: Dolichopodidae), with a taxonomic conspectus of the New World fauna, Zootaxa 1411, pp. 47-67 : 48-49

Genus MESORHAGA Schiner

MESORHAGA Schiner, 1868: 217 . Type species: Mesorhaga tristis Schiner , monotypy.

APTORTHUS Aldrich, 1893: 48 . Type species: Aptorthus albiciliatus Aldrich, 1893 , des. Coquillett, 1910: 509.

Diagnosis. Head: vertex often deeply excavated in male, with ocellar tubercle prominent; ocellar tubercle with pair of strong diverging ocellars and 3 pairs of long diverging posterior setae; vertical seta present; male sometimes with hairs on lateral frons (MSSC); eyes well separated in both sexes; scape bare, pedicel with short dorsal and longer ventral setae; first flagellomere subrectangular; arista usually dorsal.

Thorax: ac varies from 3–4 pairs long setae to reduced or absent; 5 strong dc present, not sexually dimorphic.

Legs: males sometimes with modified podomeres; femora with only weak ventral hairs; FII and FIII without preapical setae; tibiae mostly bare, sometimes with major ad and pd setae.

Wing: usually hyaline or sometimes with smoky membrane; vein M2 absent without fold or indication on membrane; M variable in curvature, from slightly curved to more strongly bent (see Figs. 1 c, 3d); crossvein bm-cu totally absent; crossvein dm-cu straight; halter sometimes sexually dimorphic, black in males and yellow in females.

Abdomen: tergum 6 sometimes ventrally expanded with abundant setae; tergum 7 enclosing elongate epandrial base (e.g. Fig. 2 a), with sternum 7 reduced or lost; epandrium usually elongate and cylindrical; hypopygial foramen left lateral and positioned in basal third to basal half of epandrium; phallus and hypandrium arising from base of epandrium; hypandrium tapering, narrow, and symmetrical, without left lateral arm; phallus long and narrow, and can be protruded out from the epandrium ( Figs 3 b, 3f); epandrial lobe usually flattened and ovate, bearing strong seta on inner margin and apically; strong epandrial seta present at base of epandrial lobe; surstylus usually with 3–4 short overlapping arms; cercus curved and tapering, usually with strong basolateral setae, and with species diagnostic shape and setae.

Remarks. Mesorhaga is an almost cosmopolitan genus that can be readily recognized by a combination of venation and male postabdominal structure. Although the unbranched and curved vein M of Mesorhaga has been used as a key character for the genus, the loss of M2 (i.e., an unbranched M) has been independently derived several times within the Sciapodinae , variously as a MSSC or in both sexes. Other diagnostic features that help distinguish it from other members of the Sciapodinae include a single strong vertical seta in both sexes, hypopygial foramen positioned from basal third to basal half of epandrium, hypandrium narrow, elongate, and symmetrical, without a left lateral arm, and the cercus massive, clavate and often curved.

The habitus, venation, and derived male postabdomen make Mesorhaga one of the few demonstrably monophyletic genera of the subfamily Sciapodinae (for discussion of morphology, systematics and extralimital fauna, see Bickel 1994).

Figures

FIGURE 1. Mesorhaga lacrymans Parent: a. hypopygium, left lateral. b. male distal tarsus I, dorsal. c. male wing, dorsal. M. cocori n. sp.: d. hypopygium, left lateral. M. sarukhani n. sp.: e. hypopygium, left lateral. M. funebris Parent: f. hypopygium, left lateral. M. hule n. sp.: g. hypopygium, left lateral.

FIGURE 2. Mesorhaga adunca Van Duzee a. hypopygium, left lateral. M. falciunguis n. sp.: b. hypopygium, left lateral; c. male distal tarsus I, posterior. M. villanuevi n. sp.: d. hypopygium, left lateral.

FIGURE 3. Mesorhaga isthmia n. sp. a hypopygium, left lateral. b. male postabdomen with phallus extended, left lateral; c. male tarsus I, posterior view. d. male wing, dorsal. M. baadsvicki n. sp.: e. hypopygium, left lateral. M. mexicana n. sp.: f. hypopygium, left lateral.