Silba cascadens, Introduction & Fallén & Morge, 2007

Introduction, Iain, Fallén, Lonchaea & Morge, Setisquamalonchaea, 2007, New pecies of Lonchaeidae (Diptera: Schizophora) from Asia, Zootaxa 1631, pp. 1-32 : 18-20

Silba cascadens sp. nov.

Description: Holotype male: Head: Eyes bare. Frons matt black, dulled by microsculpture, parallel sided on its central part where it is approximately two thirds eye width, frontal and interfrontal setulae very short, only about one tenth the length of orbital setae, slightly longer setulae present on the anterior margin. Orbital plate also slightly dulled by microsculpture, bare of setulae. Lunule with three / four setulae present on each side, ground colour light brown but covered with intense silver dusting. Face and parafacials also silvered. Anterior genal setulae in a single row of five along mouth margin, the basal two strong and setae-like, by far the strongest setulae on the genae. Second antennal segment reddish-brown. Antennal flagellomere entirely black, just with a trace of brown at extreme base on inner surface, about two and a half times as long as deep. Arista yellow on the basal third, long plumose, plumosity at its maximum extent almost one and a half times the depth of antennal flagellomere.

Thorax: Disc shining black with moderate dusting in the pre-scutellar area, covered with moderately dense setulae approximately one quarter the length of orbital setae. Pleurae dusted. Anepisternum with two strong anterior setae and three posterior strong setae, upper posterior setae slightly weaker and situated anterior to the other two. Katepisternum with two setae, the posterior one slightly stronger and situated at a level just dorsal to the anterior, no setulae ventral or posterior to these setae. One propleural and one shorter and finer stigmatical setae. Scutellum dusted grey-metallic on the disc, on margin on each side between the apical and lateral setae with six to seven setulae in multiserial rows, upper row with one or two stronger setulae whilst lower rows contain shorter setulae, two setulae present between apical setae. Squamae pale with pale margins and fringes. Wings clear with light yellow veins. Wing length 4.0mm. Legs: entirely black.

Male terminalia; Figs. 35–38. In lateral view epandrium twice as high as wide, with a small anterior process, posteroventrally covered in multiple rows of short setulae with longer ones posteriorly along the margin, none of these particularly strong. Cerci not heavily sclerotised, upright and rounded apically, relatively small, less than half height of epandrium, with moderately long, well spaced setulae apically, some shorter ones on the ventral margin. One projecting tooth visible at the base of the cerci on one side, on the other side there are two teeth in this position. In ventral view surstyli with a vertical row of eight small black teeth extending down the inner surface below the posteriorly projecting tooth, the upper five in a distinct row, the lower three slightly more scattered. One thin sharp spine present on each side below the base of the cerci. Aedeagus in lateral view with a relatively wide basal portion from which arises the thin recurved apical part, a pair of thin finger-like processes arising from the basal part and extending below the upwardly curving apical portion.

Female: unknown.

Differential diagnosis: This species belongs to the Silba abstata McAlpine, 1956 group of species all of which are rather small, with a relatively short antennal flagellomere, an elongate epandrium with short cerci and a row of teeth on the inner surface of the surstyli situated parallel to the ventral margin. It is most closely related to S. abstata itself which also has a pale squamal fringe and basal processes on the aedeagus, but, this species differs from S. abstata in having a wider frons, a slightly dulled orbital plate, fewer setulae on the lunule, longer aristal plumosity and clear wings. In the male terminalia of S. abstata ( McAlpine, 1956) the epandrium is three times as high as it is wide, compared to twice as high in this species and the inner teeth on the surstyli are more regularly spaced. The aedeagus of both species is similar in shape.

TYPE MATERIAL: Holotype male. THAILAND: Nan Prov. Mae Charim waterfall, No.25, over and along rivulet, 7–8.ix.04, leg. Papp & Földvári.

Paratypes. One male with the sane data as the Holotype. Trang Prov. Khao Chong Botanic gardens, rainforest, 22.xi.04, No. 43, leg. Papp & Földvári. 1 male .

Holotype and paratypes in the HNHM .

Etymology: The specific epithet refers to the waterfall or cascade where the holotype was captured.