Description of
Nebritus Coquillett
(Diptera: Therevidae: Therevinae)

Nebritus Coquillett (1894:98) Type species: Nebritus pellucidus Coquillett (1894:98) by original designation. Zionea Hardy (1938:144). Type species: Zionea tanneri Hardy (1938:144) by original monotypy. Synonymized by Irwin and Lyneborg (1981a:249).

Derivation of name: nebrites (Greek, feminine) = like a fawnskin.

Diagnosis. The genus Nebritus Coquillett is associated with the genera Dialineura Rondani and Pallicephala Irwin and Lyneborg by possessing fine setae on the posterior surface of the middle coxae, by having the prosternum with fine setae in and around its central depression (exception P. quebecensis), and with the scape being wider than the width of the first flagellomere. It is separated from these two genera in not having the posterolateral corners of the epandrium strongly projecting nor the epandrium extending to or beyond the apex of the cerci or hypoproct. At this time, no definitive sister-group relationship is proposed for Nebritus with any other therevid genus.

Small- to medium-sized, robust flies. Males more slender and smaller than females.

Description
Head (Fig. 1, 13, 29). Eyes dichoptic in both sexes, facets equal; antenna (Fig. 2, 14, 30), length 1.0-1.4 times head length; scape variable; pedicel ovate; flagellum awl-shaped, tapered apically; style subapical, one-segmented; terminal spine short; frons broad, lateral margins converge dorsally; frontal calli prominent; parafacial broad, tentorial pit large, distinct, glossy; clypeus concave; maxillary palp one-segmented (Fig. 3), cylindrical, apex rounded; setae scattered over entire frons, abundant on gena and maxillary palp, absent on eyes, parafacial, and clypeus.

Thorax. Macrosetae: np 2-4, sa 1-3, pa 1, dc 1-2, sc 2. Setae on scutum variable; prosternal setae white; setae abundant on propleuron, scattered over entire anepisternum and katepisternum, absent on remaining pleural sclerites.

Wing (Fig. 4). Hyaline to pale smoky brown; veins brown; pterostigma indistinct to pale brown; setulae absent; length of R4 0.9-1.0 times length of R5; cell r4 large; length of cell r4 2.5-3.1 times width; veins M1, M2, and M3 originate separately from apical margin of discal cell; cell m3 widely open; discal cell acute basally; 5 posterior cells; cell cup closed with short petiole; m-cu/r-m subequal.

Legs. Coxae moderately long; setae elongate, scattered on anterior and posterior surfaces of coxae; forecoxa with 2-3 black, apical macrosetae.

Abdomen. Slender to moderately broad, gradually tapering from segment 3 onward; male dorsum silvery gray pruinose; female dorsum extensively gray pruinose, some species with a distinct, dark, glossy, anterior band on various tergites.

Male Terminalia (Fig. 5-10, 15-20, 31-36).
Tergite 8 subrectangular to bilobed (Fig. 5, 15, 31) often strongly constricted medially; sternite 8 (Fig. 7, 17, 33) rectangular to bilobed, moderately reduced; epandrium (Fig. 5, 15, 31) shorter medially than wide, its posterolateral corners infolded; cerci rather large, free, well sclerotized, generally not extending beyond apex of hypoproct; hypoproct large, extending nearly to anterior margin of epandrium with a membranous attachment to anterior margin of dorsal apodeme of aedeagus; hypoproct as a whole well sclerotized, occasionally keel-shaped apically below cerci; parameral apodeme (Fig. 6, 16, 32) not attached to aedeagus; distiphallus (Fig. 8-10, 18-20, 34-36) rather long compared to rest of aedeagus, downcurved; dorsal apodeme broad, anterior margin deeply emarginate; ventral apodemes small, not bifurcated medially; ejaculatory apodeme variable; ventral lobes of gonocoxites large, spoon shaped, directed obliquely upward, with distinct attachment to ventral surface of aedeagus; parameral process (Fig. 6-7, 16-17, 32-33) long and slender; gonocoxites (Fig. 7, 17, 33) not united ventrally except by a membrane; gonocoxite in lateral view broadly rounded posteriorly; hypandrium (Fig. 6-7, 16-17, 32-33) broad throughout, united with anterior margin of gonocoxites for a rather long distance.

Female Terminalia (Fig. 11-12, 21-22, 37-38). Tergite 8 subrectangular, generally longer than wide, posterior margin slightly emarginate. Tergite 9+10 fused, with strong acanthophorite setae. Cercus subtriangular, membranous with numerous, fine, moderately long setae. Sternite 8 large; longer than wide; posterior margin with narrow, median incision. Sternite 9 greatly modified, invaginated above sternite 8 to form internal furca which is closed anteriorly. Sternite 10 membranous; subtriangular; setae short, thick.

Immature Stages. Not previously described. Here described for Nebritus powelli.

Biology. Adults of Nebritus are found in montane habitats and coastal sand dunes. They have been collected from 10 January to 27 July on coastal dunes, on wet sand, and along sandy creek bottoms; on Pinus monophylla Torr. and Frém. in Frém., Salix sp., and Adenostoma sp.; and in Malaise traps. Larvae have been collected in coastal sand dunes.

Distribution. Nebritus is a Nearctic genus ranging from Baja California Norte to northern California and eastward to western Nevada and southwestern Utah.

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Text from Webb & Irwin 1991a