Billaea Robineau-Desvoidy, 1830

Zhang, Chun-Tian, Shima, Hiroshi, Wang, Qiang & Tschorsnig, Hans-Peter, 2015, A review of Billaea Robineau-Desvoidy of the eastern Palearctic and Oriental regions (Diptera: Tachinidae), Zootaxa 3949 (1), pp. 1-40 : 3-4

Billaea Robineau-Desvoidy, 1830

Billaea Robineau-Desvoidy, 1830: 328 . Type species: Billaea grisea Robineau-Desvoidy, 1830 (= Dexia pectinata Meigen, 1826 ), by monotypy [Palearctic].

Synonyms. See Herting & Dely-Draskovits 1993: 356 for the genus and references prior to 1993.— Crosskey 1976: 177.— O’Hara & Wood 2004: 22.

Diagnosis. See characters of Billaea in the Introduction. Pregonite long and bent posteriorly, distiphallus long plate-like.

Generic redescription. Head. Vertex of male 0.12–0.25, female 0.28–0.4 of head width; fronto-orbital plate with dense fine hairs outside row of frontal setae; genal height 0.3–0.7 of eye height and at least as long as flagellomere 1; parafacial usually bare, rarely haired, parallel-sided, 2–3 times as wide as flagellomere 1; facial carina often low or undeveloped, sometimes developed and distinct (e.g., B. pectinata with high and pointed facial carina); male usually without outer vertical seta; vibrissa inserted above or at lower margin of face; occiput with 1– 4 rows of black hairs behind postocular setae. Antenna falling short of lower margin of face by 0.3–1 times length of antenna, flagellomere 1 1.5–4.5 times as long as pedicel; arista pubescent or plumose; palpus developed. Eye bare.

Thorax. Prosternum bare, 1.5–3 times as long as wide; proepisternum haired, katepimeron usually haired on anterior 1/2; postpronotal lobe with 2–5 setae; 3–4 presutural and 4 postsutural dorsocentral setae; scutellum with 3–4 pairs of marginal and 2–6 short discal setae; 1 strong anepimeral seta, 2 or 3 katepisternal setae. Posterior spiracle with anterior and posterior lappets unequal in size, posterior lappet subcircular. Wing. Second costal sector bare ventrally, costal spine absent; base of vein R4+5 with 2–3 short black hairs on dorsal and ventral surfaces; cell r4+5 usually open, bend of vein M angulated, usually with a short appendix. Legs. Medium in length, fore tarsi about as long as, sometimes longer than head height; fore tibia with 1–2 posterior setae, mid tibia with 2–3 anterodorsal setae, hind tibia usually with a comb-like row of anterodorsal setae of rather uniform length, male sometimes and female with 1–3 strong anterodorsal setae among them, and 2 preapical dorsal setae.

Abdomen. Syntergite 1+2 medially excavated to posterior margin, usually without, sometimes with median marginal setae in both sexes; tergites 3 and 4 without median discal setae; tergites 4 and 5 each with a row of marginal setae. Male terminalia. Sternite 5 usually with wide and blunt posterior lobe, median cleft wide and deep. Surstylus often rounded at apex; cerci strongly narrowed and pointed at distal half; pregonite long and bent posteriorly; postgonite shorter than or equal to basiphallus; distiphallus with long plate-like sclerotized dorsal and membranous ventral part and narrow and long membranous apical part.

Hosts. The larvae of Billaea are parasitic on coleopteran larvae dwelling in rotten wood, such as Scarabaeidae , Cetoniidae or some Cerambycidae , or they develop in wood-boring larvae of Cerambycidae , or—rarely—also some Curculionidae or Buprestidae ( Herting 1960: 127; Mesnil 1980: 4; Tschorsnig & Herting 1994: 156; Shima 2006: 10).

Distribution. Worldwide: Afrotropical, Palearctic, Oriental, Australasian, Nearctic and Neotropical regions ( O’Hara 2013, 2014).

Remarks. Billaea appears to have no apomorphic characters to support its monophyly at present. However, it is practically distinguished from other genera of the Dexiini by some combination of characters. It differs from Dexia Meigen by second costal section of the wing bare ventrally and facial carina usually undeveloped, and differs from Estheria Robineau-Desvoidy by the proepisternum haired and abdominal tergites 3 and 4 lacking median discal setae. Billaea is closely similar to Dinera Robineau-Desvoidy in morphological characters including the male terminalia. Some species, especially those of females, have rather intermediate characters between both genera, such as hind tibia of some males and most females with 1–3 stronger setae among a row of irregular and dense anterodorsal setae, and fore tarsi slightly longer than head height, vertex of male about 1/7 of head width. Billaea may be distinguished from Dinera in having some dense minute hairs on fronto-orbital plate, facial carina usually low and undeveloped, fore tarsi about as long as head height, but these may also be variable in some species, and the hosts of the two genera are different. It is possible that Billaea is combined with Dinera as a single genus when bare second costal section of the wing and haired proepisternum are considered as apomorphic characters to support their monophyly. The systematic relationship of these genera has not been solved in our study of phylogenetic analysis of morphological characters, and it will be well explained by molecular studies in the future.