Albistyla, Marshall, Stephen A., 2014

Marshall, Stephen A., 2014, Albistyla, a new genus of Neotropical Limosininae (Diptera: Sphaeroceridae), Zootaxa 3793 (2), pp. 257-264 : 257-259

Albistyla new genus

Type species: Albistyla spatulisterna new species

Generic diagnosis. Albistyla is characterized by a suite of male abdominal synapomorphies including a white surstylus terminating in a broad, pale, scale-like bristle, an enlarged but simple fourth sternite, and a strongly modified fifth sternite with three pairs of lobes posteriorly and anterior margin extended under fourth sternite. Diagnostic characters include three interfrontal bristles with the middle pair greatly enlarged and cruciate, R2+3 long and slightly sinuate, R4+5 almost straight and not bypassed by the costa, male synsternite 6–8 separate from epandrium, hypandrium long and Y-shaped with arms articulated to (not fused with) epandrium, and known females with tergite 10 (epiproct) absent or greatly reduced and cercus very short.

Generic description. Body length 2.0– 2.3 mm without wing, wing length 1.7–2.0 mm. Head ( Fig. 15 ) mostly dark brown with anterior part of frons and face sometimes reddish brown; gena brown. Face broad and prominent, gradually sloped down from a bulging lunule as wide as pedicel. Clypeus narrow, dark, ventral margin microtrichose. Palpus tapered, with thin apical and preapical ventral bristles. Eye 1.7–2.0X as high as gena, vibrissa strong, subvibrissa and anterior genal bristle slightly enlarged. Gena separated from postgena by a prominent dark vertical strip. Antenna brown, medial part of scape with 1 large proclinate bristle and 2 minute bristles, pedicel with several long bristles along distal margin and a single inclinate preapical dorsal bristle, first flagellomere with arista arising on distal third of outer margin. Arista long (slightly longer than head + thorax), aristal hairs twice as long as width of aristal base. Three pairs of interfrontal bristles, upper and lower pairs small to minute, middle pair very strong and cruciate. Orbital bristles in 2 pairs, posterior pair 1.5X longer and thicker than anterior; interfrontal strips elevated. Orbital setulae minute, in a single row. Postvertical, inner vertical, outer vertical and ocellar bristle strong; postocellars weak but distinct and inclinate; inner occipital bristles small but distinct.

Thorax dark brown, pruinose. Prosternum linear, membrane flanking prosternum bare. Dorsocentral bristles usually in 2 strong subequal postsutural pairs ( Fig. 15 ), presutural dorsocentral setula sometimes slightly enlarged; acrostichal bristles in 6 rows between anterior dorsocentrals. Several (3–6) small and 1 large postpronotal bristles, 2 notopleural bristles (posterior notopleural bristle shorter and on a prominent callus), 1 supra-alar bristle, 1 intraalar bristle. Anepisternum bare, middle portion depressed so that posterior margin forms a ridge; anepimeron prominently bulging, with prominent, circular upper part often narrowly margined in black; katatergite flat and depressed, flanked by vertical walls of anatergite and anepisternum. Meron flat and depressed. Scutellum 1.3X as wide as long, with 4 marginal bristles. Legs brown, fore coxa large, flattened, half as long as femur. Mid tibia of both sexes ventrally usually with only an apical bristle, but also with a mid-ventral bristle in A. occulta , dorsally with 3 proximal bristles (2 anterodorsal, 1 smaller posterodorsal) and 3 distal bristles (large anterodorsal, small posterodorsal and a larger more distal dorsal bristle). Hind tarsomeres one and two enlarged and with dense posteroventral comb of golden setulae, tarsomere one twice as wide and half as long as tarsomere two.

Wing ( Fig. 15 ) completely hyaline, length 1.2 to 1.3X maximum width. Costagium with two small bristles. R2+3 slightly sinuate; costa terminating at the tip of R4+5, R4+5 almost straight, apical 1/3 slightly bent towards costa and ending before wing tip; second costal sector 0.9–1.1X as long as third costal sector; dm-cu slightly longer than r-m. Discal cell rounded on posterior corner or closed by a straight vein, stump vein CuA1 present or absent (intraspecifically variable). Anal vein gently curved. Alula narrow, almost parallel-sided. Halter brown.

Male abdomen: S4 large, subquadrate, S5 anteriorly produced into a broad apodeme almost as large as S4 and normally retracted under (dorsal to) S4. Posterior margin of S5 forming a multi-lobed, complex anterior margin to the genital pouch. Ring sclerite large and distinct. Synsternite 6–8 narrow dorsally and ventrally; S8 entirely free from epandrium; S6 running as a thin strip under the complex posterior margin of S5. Hypandrium simple, Yshaped with narrow anterior apodeme and long posterior arms separate from epandrium. Epandrium short, symmetrical, with sparse, small bristles. Cerci small, not clearly delimited from epandrium, narrowly fused dorsally. Subepandrial sclerite with broad lobes articulating with surstylus. Surstylus with a simple, white, tapered basal section and a pale distal scale. Basiphallus very large, with a prominent posterior process (epiphallus); distiphallus relatively small and mostly membranous, anterior surface spinulose. Postgonite simple, distally tapered and bent anteriorly.

Female abdomen: Abdomen short, T10 (epiproct) reduced, pale or membranous and without bristles. Cercus short and rounded, with short bristles. Spermathecae (2+1) with sclerotized parts of ducts relatively long and sharply recurved.

Etymology. The generic name refers to the strikingly pale surstylus.

Biology. Most specimens of Albistyla considered here were collected in green decaying vegetation associated with recently fallen trees, although both A. fimbriata and A. spatulisterna have also been collected amongst decaying vegetation in kitchen compost piles near forested habitat at neotropical research stations, and the entire type series of A. occulta was taken in a Malaise trap over a small forest stream in Ecuador. It is probable that all species in this genus develop as bacterial grazers in moist decomposing vegetation. Species of Bregmosina Marshall have similar habits ( Marshall 2013), and have been collected along with Albistyla species.

Relationships. Albistyla species are superficially similar to Bregmosina, another limosinine with cruciate interfrontal bristles and a relatively broad and short face. These two genera differ widely in most other characters, including genitalia, wing venation, and chaetotaxy, and there is no basis for suggesting a close relationship. The most striking defining character of Albistyla is the modification of sternite 5 into a broad anterior apodeme running over (dorsal to inner surface of) sternite 4 and a complex, multi-lobed posterior margin. Somewhat similar modifications of sternite 5 are seen in the Holarctic genus Apteromyia Vimmer , but there are no other grounds for postulating a close relationship between these two otherwise dissimilar genera. Although the relationships between Albistyla and other limosinine genera are not clear, the relationships between the species of Albistyla are unambiguous and the monophyly of the genus is supported by several synapomorphies (male sternite 5 with a broad anterior apodeme running over sternite 4; posterior margin of sternite 5 forming a complex anterior margin of the genital pouch, strongly differentiated from anterior part of sternite and including multiple lobes; surstylus with a simple main body and a large, flattened scale-like spur; surstylus white). Within Albistyla there seems to be one species found in both Central America and South America, and one pair of sister species ( A. spatulisterna and A. occulta ) split between Central America and South America.

Figures

FIGURE 15. Albistyla spatulisterna female, photograph of mounted specimen.