Atriadops irwini Barraclough, 2022

Barraclough, David A. & Colville, Jonathan F., 2022, The first species of Nemestrinidae (Diptera) endemic to Madagascar: A remarkable new species of Atriadops Wandolleck, 1897, Zootaxa 5196 (1), pp. 145-150 : 147-149

Atriadops irwini Barraclough sp. nov.

( Figs 2A–2D )

Type material: 1♂, Madagascar: Antsiranana Province: HOLOTYPE: ♂: “Sakaramy, 7 km N Joffre- / ville; hand netted in lowland / tropical forest; 7.i.2007; ME Irwin / 425 m; 12°26.77ˈS, 49°14.10ˈE” (in NMSA).

Etymology. The species is named for Dr Michael E. Irwin, Emeritus Professor, Department of Entomology, University of Illinois, who collected the holotype. It recognises his long and distinguished career and his contribution to Afrotropical dipterology, in particular the taxonomy and systematics of lower Brachycera.

Diagnosis. Unlike all the African material examined and unlike A. iavanus , A. amamioshimensis and A. macula , the style is short and at most about one and a half times the length of the postpedicel. In the three species referred to above, the style is longer and at least three times the length of the postpedicel. In addition, and based on comparison with African material, the antennae in A. irwini sp. nov. are more closely approximated and more deeply recessed in the facial groove. They are also partially concealed by a denser and more elongate pile at the anterior extent of the frons. These pronounced differences are evident in Fig. 2B . The only species not reviewed are A. aruanu and A. westwoodi from isolated localities in eastern Indonesia and eastern Australia, respectively. It is extremely unlikely that they could be conspecific with A. irwini sp. nov.

Description (based on male holotype). Body length: 10.47 mm. Wing length: 10.72 mm (and see Fig. 2A for dorsal habitus). Head ( Fig. 2B ): Colouring: frons and face yellow to brown, but ocellar tubercle blackish, as on occiput (except at lower extent); antenna yellow to brown, scape somewhat darker. Pile: brown, short and sparse on ocellar tubercle, brown to golden and longer and much denser over frons, longest and most dense at anterior extent of frons, projecting over deep facial excavation, where length is subequal to that of antennae, thereafter cream to golden below facial excavation where sparser and partially absent at anteroventral extent of eye. Eyes closely approximated, but notably not touching in region anterior to ocellar tubercle. Ocellar tubercle just visible in profile, length subequal to that of scape, pedicel and postpedicel. Frons with lower extent clearly visible in profile. Antennae deeply recessed in facial excavation and difficult to discern, given density and length of pile at anterior extent of frons; relatively close together, at most 3.0 × length of scape, pedicel and postpedicel apart; scape difficult to discern, apparently about 1 / 2 length of pedicel and lacking vestiture; pedicel with elongate yellow pile along dorsal and ventral margins; postpedicel ovoid, slightly longer than scape; style short, about 1.0–1.5 × length of postpedicel. Thorax ( Fig. 2A ): pile creamy white to golden on scutum and scutellum, shorter and sparser posteromedially anterior to scutellum. Scutum with paired median and paired sublateral vittae, all black in colour; median vittae shorter and noticeably narrower, about 2 / 3 length of sublateral vittae. Pleuron yellow to brown with irregularly distributed long, white pile; pile entirely absent between fore and mid coxae and on katepisternum; ground colour noticeably black on ventral part of katepisternum and between fore and mid coxae. Legs: colour mostly yellow-brown, although tibiae and tarsi somewhat paler. Fore leg: coxa with anterior and ventral surface bearing elongate, white, dense pile; pile also elongate and dense on posterior face of femur, here cream at base, but ranging from pale brown medially to dark brown apically. Mid leg: without significant pile, this present on tibia but very short. Hind leg: only femur with significant pile, but this variably present; femur pile relatively elongate and dense dorsobasally and along ventral margin (length here reaching depth of femur). Wing ( Fig. 2C ): relatively broad basally and narrowed in apical 3 / 5; apex acutely pointed just posterior to insertion of vein M 1 on margin. Creamy white streak reaching from diagonal crossvein to costal margin as in other Atriadops species, but notably slender and width subequal to distance between veins R 1 and R 2+3 along wing margin. Venation otherwise unremarkable and supernumerary veins absent. Colouring of membrane rather indistinct dark brown, but paler on parts of posterior 1 / 3 to 1 / 2 of wing, although colouring irregularly distributed; darkest brown infuscation concentrated around some wing veins at mid-length of wing. Abdomen ( Fig. 2D ): colour: tergite 1 dark brown; tergites 2 to 7 a mixture of yellow-brown and dark brown, with darker colouring somewhat anteromedial and there more extensive, but progressively less apparent and irregularly distributed until only small dorsomedial marking on tergite 7 with this narrower than width of terminalia. Sternites almost entirely yellow-brown. Pile: short on tergites, but elongate and pale along lateral margins; small cluster of sparse, erect, dark vestiture on anteromedial margin of tergite 2 (although this not extending laterally), this vestiture similarly positioned on successive tergites but recumbent and less extensive (barely visible on tergite 7), on sternites short and white along posterior margins, length typically less than length of next sternite. Terminalia: cerci apparently short in profile, at most subequal in length to tergite 9. Posterolateral process of tergite 9 ( Nagatomi 1978: 609) broad along much of length, but noticeably tapered apically and extreme apex appearing quadrate.

Discussion: Based on experience with Nycterimyia , there is a need for extreme caution when assessing species characters in the Trichopsideinae ( Barraclough 2005 a, 2006). In Nycterimyia , for example, there is intraspecific sexual dimorphism in wing patterning and shape and in the shape of the antennal style ( Barraclough, 2006). Although an array of African specimens of Atriadops was examined by one of us (DB), representative taxa from the remainder of the genus’s range were not examined. However, several publications (and associated illustrations) on the extralimital fauna were examined in detail (all cited elsewhere in this text). Based on this analysis, A. irwini sp. nov. is a striking new species.

Unlike the African material of Atriadops , A. irwini sp. nov. was collected from tropical rainforest. Given the importance of the holotype, it was not dissected. The terminalia are therefore not illustrated and the limited description is based on in situ appearance. Further entomological field surveys in Madagascar’s forested habitats may reveal additional species of Atriadops and a richer endemic fauna of Nemestrinidae ( Glaw et al. 2019) .

Figures

FIGURES 2A–2D. External characters of Atriadops irwini sp. nov. 2A. Dorsal habitus (wings flexed downwards). 2B. Frontal view of head, showing development of pile and form of antenna. 2C. Dorsal view of wing, showing patterning and infuscation. 2D. Dorsal view of abdomen, showing patterning and distribution of pile.