Megalothoraca Hendel, 1911

Wendt, Lisiane Dilli & Marinoni, Luciane, 2019, Taxonomic revision of Megalothoraca (Diptera: Richardiidae) with description of a new species, synonyms and new combination, Zoologia (e 31456) 36, pp. 1-15 : 2-3

Megalothoraca Hendel, 1911

Megalothoraca Hendel, 1911a: 395 (type species: Megalothoraca pterodontida Hendel, 1911 , by monotypy); Hendel 1911a: 182 (key); 1911b: 5, 50–52 (key, redescription, note, distribution, spp. list); Hennig 1938a: 121 (citation); 1838b: 9 (citation); Aczél 1950: 43 (catalogue); Steyskal 1968: 5 (catalogue); Hancock 2010: 877 (key); Carvalho et al. 2011: 43 (key); Alencar et al. 2013: 202 (citation); Wendt and Ale-Rocha 2014b: 306, 308 (citation, discussion); 2016: 592 (catalogue of Colombia, note). Phlebacrocyma Enderlein, 1912: 105 (type species: Phlebacrocyma undulosum Enderlein, 1912 , original designation); Hennig 1938a: 121 (citation); Aczél 1950: 44 (catalogue); Steyskal 1968: 5 (catalogue; synonymy).

Diagnosis and comments. Megalothoraca species are large (8.0–12.4 mm), with thorax well developed and wing generally longer than body, mid and hind legs long and slender, fore leg generally conspicuously more robust than the others (at least in males), and abdomen oval. Males and females of the included species are unique in lacking spine-like seta on the posteroventral surface of the mid and hind femora; mid femur with only one anteroventral spine-like seta and hind femur with one or two such setae (e.g. Fig. 40); vein R 2+3 with two conspicuous curves on apical third ( Figs 16, 48, 57), and medial spurious vein short ( Fig. 48) (absent in M. flava Enderlein, 1912 ). Additionally, Megalothoraca males have costal vein conspicuously bowed anteriorly and thickened on medial portion (unmodified in females) ( Figs 5, 18, 22), thorax distinctly well developed, setae on the fore and mid coxae stout ( Fig. 7) and hind coxa setulose on posterior surface (males of other Richardiinae genera have unmodified costal vein, thorax proportional to the rest of body, unmodified setae on the coxae and hind coxa bare posteriorly – also setulose in Setellia Robineau-Desvoidy, 1830 ).

The following features of Megalothoraca are shared with Euolena egregia (Gerstaecker, 1860) and species of Bathachophtalmum Hendel, 1911: antero- and posteroventral spine-like setae on fore femur distinctly more numerous and robust than on mid and hind femora; palpus straight. Moreover, species of Megalothoraca are similar to species of Batrachophthalmum , Euolena Loew, 1873 (in part) and Hemixantha Loew, 1873 (in part) in the male terminalia with medial surstylus bilobed at apex, and prensiseta long and inserted preapically on inner margin. Species of Megalothoraca can be easily differentiated by the venation of their wing, thorax well developed, number and thickness of the spine-like setae on mid and hind femora and the presence of setulae on hind coxa, as described above.

The general morphology of Megalothoraca species is quite regular, and the chaetotaxy of the head and especially the thorax is very similar among species. The main characteristics used to distinguish them are the coloration of the body and the wing spots. Since all species were described based on either male or female specimens and no species is known from both sexes, it is not possible to ascertain whether there is sexual dimorphism. Megalothoraca undulosa ( Enderlein, 1912) , M. ferruginea ( Enderlein, 1912) , and M. rosalyae sp. nov., (known only from females) lack a lobe on the costal vein; have narrower medial band on the wing, lack anterior spine-like setae on the fore and mid coxae, and their thorax is not as well developed as the thorax of males ( M. pterodontida Hendel, 1911 and M. flava ).

Included species. Megalothoraca ferruginea , M. flava , M. pterodontida , M. rosalyae sp. nov., M. undulosa .

Redescription. Large species, length 8.2–12.4 mm, commonly with wing longer than body (except in M. ferruginea ). Robust body, with general colour yellow ( Fig. 5) or reddish brown ( Fig. 1) to dark brown ( Figs 15, 31, 55), generally non-metallic (except abdomen of M. rosalyae sp. nov., Fig. 30). Head. In dorsal view, slightly narrower than thorax; in frontal view, wider than high. Eye oval, higher than wide. Vertex, in frontal view, straight ( Figs 10, 58) or slightly concave (in M. rosalyae sp. nov., Fig. 32). Frons not protruded anteriorly ( Figs 9, 19, 34). Ocellar triangle slightly elongate, anterior ocellus inserted on dorsal third or fourth of frons; bright, non-pollinose; convex, contoured by a weak (or stronger in M. rosalyae sp. nov., Figs 32, 33) cavity. Lunule developed. Antennal bases narrowly separated by less than width of scape; scape slightly elongate, almost as long as pedicel. First flagellomere short, at most 2.5 times longer than high. Arista long pubescent. Clypeus well developed. Palpus elongate and linear, base, mid region and apex similar in width ( Figs 9, 19). Postcranium, in lateral view, distinctly more developed on ventral two-thirds ( Figs 9, 19, 34). Chaetotaxy: setae long and robust; ocellar seta present or absent, orbital and genal setae present, postocellar and postgenal setae absent, outer vertical seta distinctly longer and thicker than inner vertical seta, with alveolus robust and elevated (e.g. Figs 10, 32, 33). Thorax. Especially in males, thorax distinctly well developed and robust ( Figs 5, 15). Scutum elongated, gradually widened posteriorly ( Figs 3, 13, 37, 54), with two longitudinal and parallel excavated rows, distinctly visible (e.g. Figs 37, 38); setulae sparsely and randomly distributed; weakly pollinose. Scutellum bare. Subscutellum developed. Prosternum, proepimeron, metasternum, and metapleuron bare. Katatergite not setulose, sparsely pollinose. Metathoracic spiracle conspicuously setulose at posterior margin. Postmetacoxal bridge completely sclerotized. Chaetotaxy: very reduced in number, scapular seta, postpronotal seta (except in M. rosalyae sp. nov.), presutural supra-alar, postsutural surpa-alar, intra-alar, proepimeral and katepisternal setae absent; postalar seta present, robust; one dorsocentral and one scutellar setae stout; posterior notopleural seta distinctly stouter and longer than anterior notopleural seta; postalar seta developed, robust. Legs. Elongate. Males with fore ( Fig. 7) and mid coxae with one robust anterior apical spine- like seta; females without these spines, only with long setae. Fore femur distinctly (in males, e.g. Figs 5, 15) or slightly (in female, e.g. Figs 39, 40) thicker than mid and hind femora (except in M. ferruginea , similar in thickness), with stout antero- and posteroventral spine- like setae (generally number in left and right femora varies in the same specimen), and more numerous than on mid and hind femora (e.g. Figs 15, 21, 39, 40). Mid and hind legs slender and long ( Figs 1, 5, 15, 31). Mid and hind femora sparsely setulose, without posteroventral spine-like seta, mid femur with only one anteroventral spine-like seta (e.g. Fig. 1), and hind femur with one (e.g. Figs 1, 15) or two spine-like setae (e.g. Fig. 40). Hind coxa setulose on posterior surface in males, bare in females. Hind femur without anterodorsal preapical seta. Wing ( Figs 16, 18, 22, 48, 57). Long, generally longer than body length, 8.0–13.8 mm. Pattern conspicuous, including basal, medial and apical marks ( Fig. 22, each mark indicated). Males with costal vein conspicuously bowed anteriorly and thickened at their medial portion in males, unmodified in females. ( Figs 18, 48). Veins bare. Vein R 2+3 with two conspicuous or inconspicuous (in M. rosalyae sp. nov., Fig. 48) curves in apical third; with short postmedial spurious vein (absent in M. flava ). Veins R 4+5 and M converging apically. Vein r-m at distal third to fifth of cell dm. Vein A 1 +CuA 2 long, becoming weaker towards margin. Alula and anal lobe well developed. Abdomen. Dark brown (e.g. Figs 20, 54), sometimes with blue sheen ( Fig. 30); metallic or non-metallic; smooth, non-punctate, and sparsely pollinose or shining. Shape oval ( Fig. 41), syntergite 1+2 with base about one third as wide as apex, and with one or two pairs of preapical laterodorsal setae. Female sternites and terminalia (only female of M. rosalyae sp. nov. was dissected and examined, Figs 42–47, 49–53). Sternite 1 present, setulose ( Fig. 42). Sternites 3–5 with short basal apodemes ( Figs 44–46). Sternite 6 with basal round hole ( Fig. 47). Oviscape short, almost as wide as long ( Fig. 53). Eversible membrane poorly sclerotized, with distal half covered with oblique rows of multidentate scales. Tergite and sternite 8 with pair of rows of moderately long setulae in distal two-thirds. Tip of cerci rounded ( Figs 49, 50). Two subglobose spermathecae strongly sclerotized. Male sternites and terminalia (only male of M. pterodontida was dissected and observed, Figs 23–29). Sternite 1 present and setulose ( Fig. 23). Sternites without basal apodemes ( Figs 23–27). Spiracles 6 and 7 present. Epandrium densely setulose, globose ( Fig. 28), in lateral view, higher than wide ( Fig. 29). Cerci, in lateral view, developed, and globose, densely setulose ( Fig. 29). Medial and lateral surstyli similar in length. Lateral surstylus without preapical projection. Medial surstylus with a submedial anterior rounded projection; bilobate apically; with long and acuminate preapical prensiseta.

Distribution. Colombia, Ecuador, Peru, Bolivia (new record).