Aphaniosoma Becker, 1903

Ebejer, Martin J., 2009, A revision of Afrotropical Chyromyidae (excluding Gymnochiromyia Hendel) (Diptera: Schizophora), with the recognition of two subfamilies and the description of new genera, African Invertebrates 50 (2), pp. 321-321 : 381-383

Genus Aphaniosoma Becker, 1903

Aphaniosoma: Becker 1903: 186 .

Type species: Aphaniosoma approximatum Becker, 1903: 186 , by original designation. Diagnosis: Concave ocp with only postocular row of setulae (none on disc), acrs in 2 rows, prpl setula present, costa broken a little beyond hu crossvein and at apex of R 1, veins R 4+5 and M 1+2 diverge towards wing apex; posterior crossvein placed before middle of wing and section of M–Cu separating basal and discal cell shorter than 2.5× length of apical section of M–Cu (usually 1.7–2.0×); strong apicoventral seta on mid tibia always present and longer than diameter of tibia at apex.

Description:

Head: Broad as thorax or a little more, more or less round to elongate, though usually longer than high; oc triangle small always equilateral; ocp concave when veiwed either from above or in profile, disc bare, only a few fine setulae at ocp foramen and along upper postocular margin; postgenal seta absent; gena narrow from 0.2 to 0.5 height of eye, vibrissal angle variously produced and rounded, but never significantly extending beyond eye margin, with 1–4 vibrissa-like setulae present; eye oval, sometimes strongly so, lying oblique or horizontal, anterior facets enlarged to about 3× size of facets at posterior pole of eye; at level of antennae eyes converge significantly and margins of fr therefore also converge; face always small, depressed with a vertical midline linear suture that may be developed into a shallow carina, otherwise face membranous; mouthparts small but normally developed with short, broad labellum, palpus small, elongate oval to slightly club-shaped; antenna small with round segment 3, sometimes slightly reniform, always pubescent especially along anterior margin, segment 1 very short, segment 2 a little longer with strong dorsal seta, arista 2-segmented, with segment 2 always dark, thin and finely pubescent. Chaetotaxy: 0–6 orb of decreasing length from back to front in a majority of species, in some species 2 long posteriorly placed orb of almost equal size; fr with a few scattered setulae, sometimes with a long proclinate pair of setae in front of oc triangle; ocellars long, proclinate and divergent; strong vti and vte, short to very short, parallel or crossed pvt.

Thorax: Robust relative to rest of fly, often with darker scutal pattern of longitudinal stripes, scut more or less triangular with smooth rounded margin and apex, more or less as long as broad. Chaetotaxy: from zero to several presutural dc setae and always with at least 1 dc postsuturally near margin with scut (when setae are reduced in number these are replaced by setulae) 1–2 pprn, 1–2 posthu, 1 ihu, 2 ntpl, 0+3 to 4+10 acrs, 0+2 to 2+6 ia, 1 pa, absent sa, pra and post ia, scut always with 1 pair of subapical and 1 pair basal; 1 anepisternal placed within upper 1/3 of posterior margin, sometimes with shorter seta adjacent and/or with fine setulae on middle of sclerite; 1 katepisternal always at upper posterior corner, sometimes with short seta in front and fine setulae in front of it or at anterior lower margin; prpl seta or (more usually) a fine setula present. Wing: About a long as body, hyaline with completely microtrichose membrane, veins brown to very pale yellow, vein separating discal from basal cell always palest; costa broken a short distance beyond hu crossvein and at junction of R 1 with costa, subcosta complete, merging with R 1 where latter merges with costa; all veins bare except for anterior margin of costa from base to apex of M 1+2 where fine setulae are interspersed with short stouter dark spine-like setulae; alula always well-developed though narrow, axillary lobe of wing round and well-developed; R 2+3 strongly arched from origin to apex of wing, where it approximates R 4+5; R 4+5 and M 1+2 always diverge and darken slightly towards wing apex. Haltere always with pale stem and paler knob.

Legs: Slender and setose only on fore femur posterodorsally, otherwise uniformly fine and very short setulose; femora never dilated; mid tibia always with a distinct dark apicoventral seta that is longer than diameter of tibia at apex; hind trochanter modified in the males of one species group, to exhibit, on its posterior inner surface, a distinct projection that may have minute spines or setulae; tarsomeres very rarely modified.

Abdomen: Somewhat dorsoventrally flattened, more or less oval, male with 6 segments, female with 8 segments; st usually poorly sclerotized; disc of tg and along hind margins with short setulae that are usually about half length of tg or much less.

Male postabdomen: Always highly modified; never with a complete external ep; cerc simple, separated (though often appearing fused in dry specimens), with short fine setulae on posterior surface and generally with 1 or 2 long fine setulae at tip; pregential st (any combination from st 4 to 6) highly modified, often ornate with diagnostic features; prg attached to inner lobe of hyp after this fuses/articulates with ep; psg originates from very base of basiph and is often a long, dark, heavily sclerotized structure; surs very variable, often fused with ep; ph always large, very variable, often complex with membranous and sclerotized components.

Female postabdomen: Segments 7 and 8 narrow and invaginated in most dry specimens, though usually distinct when the abdomen is macerated; segment 8 often with small lateral and ventral sclerites; hypr membranous and very small; cerc small, separated and only finely setulose, frequently attached to sclerite of segment 8.

Length: Body 0.75–2.2 mm; wing 0.75–2.2 mm.

Distribution: Holarctic, Afrotropical ( Fig. 69 ).

Note: Some species from other zoogeographical regions are not true Aphaniosoma , but belong to the other genera in Aphaniosominae .

Ecology: Aphaniosoma is widespread in regions with hotter and drier habitats. Most species have a strong affinity to dunes and the shores of standing water bodies, particularly saline marshes. In localities with saline marshes, the flies exhibit a strong affinity to certain plants in this order (pers. observ.): Tamarix trees, Gramineae, including Phragmites stands, Chenopodaceae. I found three species simultaneously on the flowers of (non-indigenous) Eucalyptus in Malta.The attraction to Tamarix is more than just circumstantial. It is not merely because the tree provides shade, or nectar; when alternatives for both exist in close proximity, it is still the Tamarix that very strongly attracts these flies in very large numbers and in a diversity that reflects what species exist in the area. One may speculate that species of Aphaniosoma breed either on the tree or in association with other organisms that do so, or that there is some particularly strong chemical or floral attraction.

Figures

Fig. 69. Distribution of Aphaniosoma Becker in Africa.