Neosilba flavitarsis MacGowan & Lasa, 2025

Neosilba flavitarsis MacGowan & Lasa sp. nov.

Description. Holotype Male: Head: Eye bare. Frons matt black, ratio of frons width at narrowest point above the lunule to eye width 1:2.1. Frontal and interfrontal setulae short, approximately 0.2x length of orbital seta. Orbital plate shining black, bare apart from the orbital seta. Lunule matt black, parafacial and face slightly silver-grey pollinose. Antenna black, postpedicel length to depth ratio 4.1:1. Arista short plumose, plumosity at maximum extent 0.9x depth of postpedicel. Anterior genal setulae in a single row of 4–5 along mouth margin.

Thorax: Scutum sub-shining blue-black, covered in rather dense black setula approximately 0.4x as long as the orbital seta. Anepisternum anteriorly with a vertical row of three setae posteriorly with a vertical row of six, remainder of sclerite covered in long setulae, approximately 0.5x as long as the posterior setae. Katepisternum with two setae located near dorsal margin, anterior slightly weaker than the posterior, a scattering of setulae located anterior to these near the dorsal margin. Proepisternum and proepimeron each with a single long, recurved seta. Prosternum bare. Scutellum; scutum shining blue-black as thorax, margin between lateral and apical setae with six long setulae on right side, five on left, two setulae between apical setae. Calypter white with a white fringe within which, centrally placed, are nine long black setulae 2.5x longer than the other setulae in the fringe. Wing lightly fumose, less so along posterior margin, veins brownish-black, wing length 5.0 mm. Legs black, basal and second tarsomere of all legs brownish-yellow, covered with small black setulae, fore and hind basitarsi with a ventral fringe of stiff golden setulae. Halter greyish apically, contrasting with the black stem.

Abdomen: sternite 1 bare, tergite 5 with a group of stronger spine-like setae apically. Yellow cerci often visible ventrally.

Male terminalia: ( Figs. 3–6 View FIGURES 1–6 ) In lateral view epandrium slightly higher than wide, extended into a narrow, recurved anterior process, with numerous strong setae along ventral margin and posteroventraly. Cerci fused, yellow in colour, 0.8x height of epandrium, with short black setulae on apical half. Surstylus visible on either side of anterior process of epandrium, outer margin with a regular row of strong setae. Inner surface of surstylus with a row of 6 black prensisetae along posterior margin near the base of the cerci, one additional prensisetae anterior to the most ventral prensisetae in this row. Inner surface of surstylus with approximately 15 faint lateral ridges. Postgonite Ushaped, not heavily sclerotised, densely long setulose along medial margin. Phallus, a simple J-shaped tube without processes, basiphallus dark brown with a translucent inner margin, distiphallus pale yellow and laterally flattened. there are tiny spicules present on the translucent part of the basiphallus and the base of the distiphallus.

Female: resembling the male but generally with shorter pilosity. Ratio of frons width at narrowest point above the lunule to eye width 1: 1.3. Apical segment of aculeus with a pair of dorso-basal setulae which are slightly longer than the apical segment, a pair of ventro-apical setulae the same length as the segment and a pair of dorso-apical setulae just shorter than the length of the apical segment.

Holotype: ♂ MEXICO: Veracruz, Tatatila, 19.6908N 97.1105W, emerged from Ficus carica (L.), fruit, October 2023, leg. Rodrigo Lasa. Specimen deposited in National Museum of Scotland, Edinburgh, specimen NMS-10022229 . GoogleMaps

Paratypes: 9♂ 10♀ with the same data as the holotype in National Museum of Scotland, Edinburgh, NMS-10022112, NMS-10022220, NMS-10022211*, NMS-10022193*, NMS-10022202*, NMS-10022166*, NMS-10022148 *, NMS-10022184*, NMS-10022175, NMS-10022157* and NMS-10022139*. * Indicates GoogleMaps 2 specimens on the same pin. 3♂ 3♀ with the same data as the holotype deposited in IEXA, Entomological collection of the Instituto de Ecología AC, Xalapa, Veracruz, Mexico GoogleMaps .

Taxonomic diagnosis

With a setulose lunule, two setae on the katepisternum and a group of longer black setulae in the fringe of the calypter this species clearly belongs to the genus Neosilb a, a status confirmed by DNA sequencing. It is however clearly distinct from all other described Neosilba species by having partly yellow tarsomeres. The male genitalia with their large, fused yellow cerci, which are usually clearly visible below the abdomen of males, are also distinctive within the genus Neosilba .

Until now all Neosilba species were thought to have entirely black legs. In their diagnosis of the genus Neosilba McAlpine & Steyskall (1982: 108) state “tarsi always entirely blackish” a statement repeated by Urrutia (2004: 25) who in her description of the genus also states “tarsomeros siempre negros” (tarsomeres always black). In their key to all the then known Neosilba species Galeano & Canal (2012: 363) make no mention of legs or leg colour, presumably working on the assumption that they are always black. As a result, the discovery of a species with partly yellow tarsomeres has come as somewhat of a surprise. A corresponding situation occurs in the genus Silba Macquart, 1852 where the Silba admirabilis McAlpine, 1956 species-group is distinguished by having yellow tarsomeres in an otherwise entirely black legged genus. However, this is a species group of 22 species spread across four biogeographical realms ( MacGowan, 2015, 2023) and it is likely that further DNA analysis will establish it as a distinct genus. In the other more speciose genera Lonchaea Fallén, 1820 and Dasiops Rondani, 1856 species with all black or partly yellow tarsomeres are present, so it is perhaps not too surprising that this situation should also occur in Neosilba .

Phylogenetic analysis results

The phylogenetic analysis indicated that the Neosilba species formed a distinct clade with high topological confidence (BS/BPP value 84/0.9–100/1). This provides strong support for Neosilba flavitarsis sp. nov. as a new species in the genus. The amplified sequences of the three adult flies of Neosilba flavitarsis sp. nov. were identical regardless of their sex.