Aztecatopse, Haenni & Huerta & Ch-, 2014

Haenni, Jean-Paul & Huerta, Herón, 2014, The identity of Scatopse diabolica Duda, 1928, with description of a new genus from Mexico (Diptera, Scatopsidae), Revue suisse de Zoologie 121 (2), pp. 249-260 : 250-254

Aztecatopse gen. n.

TYPE-SPECIES: Scatopse diabolica Duda, 1928 (by present designation).

DIAGNOSIS: Antennal flagellum 8-segmented; flagellomeres 2-7 twice as wide as long, with single whorl of setae on each flagellomere; palpus reniform, moderately elongate; thorax longer than wide, anterior spiracular sclerite as high as long, bearing acute anterodorsal projection, with large spiracular opening; wings densely microtrichose, R 4+5 reaching costa at or slightly beyond mid of wing, and slightly beyond level of medial fork; medial fork longer than stem, without indication of an angle or an anteriorly directed stem of vein; second costal section shorter than first; a fold present between M 2 and CuA 1; CuA 2 smoothly angled midway to apex, reaching the hind margin of the wing rather abruptly, though obliquely; halteres with setae on stem; posterior tibia with longitudinal-transverse apical comb of setae posteriorly; abdominal tergites and sternites normally sclerotized, but sternites 2-4 narrower; sternites with pilosity and scattered microtrichia present, tergites with pilosity and microtrichia diversely reduced; tergite 7 of male with a pair of more or less developed lateral posterior projections; sternite 7 with complex meso-posterior emargination; male genitalia rotated 180°, capsule-like, elongate, epandrium projected into a more or less developed beak-like projection directed ventrally in situ, with 2 pairs of elongate appendages (parameres and gonocoxites), aedeagus long and thick, diversely modified, densely pilose apically; female terminalia with tergite 8 broad, bearing spiracles, tergite 10 divided into pair of triangular sclerites, sternite 8 bilobed posteriorly or entirely divided into pair of basal lobes joined by basal sclerotized bridge; genital furca present; spermatheca rounded-oval.

DESCRIPTION: Length between 1.8 and 2.5 mm; dark brownish in general colour, shining. Head slightly higher than long or as high as long, antennae longer than head height, with 8 flagellomeres, with flagellomeres 2-7 twice as wide as long, micro-

Habitat of Aztecatopse diabolica in Coyotepec, near Otumba (Estado de México) at the location of the Malaise trap (photograph Dulce Hernández Zetina) .

sculptured and bearing single whorl of setae, last flagellomere longer, with 3 whorls of setae. Compound eyes not particularly large, with broad supra-antennal bridge, interfacetal setae present; ocelli equal in size; frons pilose under eye-bridge; face pilose; palpi reniform, moderately elongate, somewhat pointed apically with a subapical sensorial pit; labella more or less equal in length to palpi or somewhat shorter; cardo-stipes not fused medially; distal end of postmentum projecting between the labella. Occipital sensilla 2-3, close to eye margin. Thorax longer than wide, notum covered with short pilosity and a row of distinct supra-alar setae, scutellum with 12-14 longer marginal setae. Pronotal apodeme curved; anterior spiracular sclerite as high as long, setose, with large spiracular opening and an acute antero-dorsal projection; pleura with setae on antepronotum, proepimeron, proepisternum, anepisternum, katepisternum and metepimeron; meron and metepisternum devoid of pilosity and micropilosity; katepisternum largely devoid of micropilosity; anepisternum rectangular in shape; metepimeron with pointed posterolateral projection. Wings 1-2 mm long, membrane densely microtrichose, devoid of macrotrichia except usual row along posterior margin. Costa extending to middle of wing or slightly beyond (0.47-0.51), second section shorter than first; stem of M shorter than fork, forking before level of merging of R 4+5 to costa; M 1 and M 2 diverging towards wing margin, no indication of an anteriorly directed stem of vein or angle on M 1; a fold (“false vein”) present between M 2 and CuA 1; CuA 1 more or less straight, reaching wing margin or nearly so; CuA 2 with only one bend, smoothly angled about midway, reaching hind margin of wing quite abruptly but obliquely. Halteres with 1-6 setae on stem. Legs setose on all parts; anterior coxa longer than median and posterior coxa; hind femora longer than anterior and mid femora; hind tibia with a longitudinal-transverse apical comb of setae posteriorly; first tarsomere longer than second, fourth shortest; claws curved, with empodium developed. Abdomen with seven well developed pre-genital segments; tergites pilose, only very sparsely microtrichose; paired lunula-like pretergites developed in tergite 2; sternite 1 absent, sternites 2-7 normally developed, sclerotized, 2-4 narrower, all pilose and microtrichose; segment 7 with narrow anterior ring of sclerotization, tergite 7 with more or less developed paired lateral projections and an inner weakly sclerotized concave structure; sternite 7 with deep complex posterior emargination and pair of posterolateral lobes more or less developed; male genital capsule elongate, epandrium ventrally (when genital capsule in situ) projected into more or less developed beak-like projection; aedeagus long and thick, sperm duct modified, thickly microtrichose apically; parameres elongated, widening and bearing setae apically, articulated to base of aedeagus through a small sclerite; gonocoxites more or less claw-like or spatulate, elongate, apically pilose. Sperm-pump large. Female as male in general features; tergites 1-4 only very sparsely pilose, devoid of micropilosity, tergites 5-8 pilose, 7-8 also micropilose; abdominal segment 7 not strongly modified, posterior margins of tergite and sternite somewhat emarginated; tergite 8 broad, with slightly emarginated posterior margin, bearing pair of basal spiracular openings, tergite 10 divided into pair of triangular sclerites; sternite 8 complex, more or less divided, bilobed, with pair of submedian pointed posterior projections or with lateral lobes widely separated and joined medially by a bridge-shaped structure; genital furca present, weakly sclerotized; spermatheca rounded-oval.

Species included. Nearctic. Scatopse diabolica Duda, 1928 and three additional, yet undescribed species from Mexico (Huerta & Haenni, in prep.).

ETYMOLOGY: The new genus is named after the former Aztec Empire which extended over Central Mexico from the 14 th to the 16 th centuries. The name is a contraction of the words ‘ Aztec ’ and ‘ Scatopse ’ and the gender of the new genus is feminine .

DISCUSSION: The new genus presents a mixture of characters of the Swammerdamellini and the Scatopsini making its placement difficult. On one hand, the shape of CuA 2 reaching costa rather abruptly (but more obliquely than in most genera of Swammerdamellini), the short costa and radial sector reaching costa about middle of wing or hardly beyond, with second costal section shorter than first are considered synapomorphies of Swammerdamellini ( Cook, 1972). This is also the case for the shape of the palpus, reniform-elongate and more or less pointed apically ( Cook, 1972). However, a somewhat elongate, apically pointed palpus is also present in Reichertella of the Scatopsini, which also has a rather similarly abruptly bent CuA 2 joining the hind margin of wing obliquely. Moreover, R. nigra (Meigen, 1804) , the type species of Reichertella , also has a shortened costa and R. On the other hand the presence of an acute antero-dorsal projection on the anterior spiracular sclerite is a clear synapomorphy of the Scatopsini (which includes Scatopse , Apiloscatopse and Reichertella ) according to Amorim (1982). Furthermore, the genital capsule presents several features characteristic of the Scatopsini: the elongate apically modified aedeagus, the presence of gonocoxites, and the development of parameres. The sclerotized abdominal sternites 2-6 and the short, practically as high as long anterior spiracular sclerite are plesiomorphic features seen in the Scatopsini, but also present otherwise in Pararhexosa Freeman of the Swammerdamellini.

The holotype of Pararhexosa flavipalpis (Edwards, 1928) was re-examined by the senior author (JPH) in the course of the present study. In this species, the anterior spiracular sclerite is devoid of an anterodorsal pointed projection and the palpus is large, reniform, broadly rounded at both ends, not more or less pointed apically as in Reichertella and the new genus. The key problem in this matter is thus the position of Pararhexosa and its delimitation. It is most unfortunate that the type species of this genus is known from the female only. The female terminalia of Aztecatopse gen. nov. do not seem to differ strongly from those of Pararhexosa regarding the more or less bilobed sternite 8. The development of tergite 8, however, is very different: it is almost entirely divided into a pair of lateral lobes by a deep posterior incision in Pararhexosa , while it is entire, hardly emarginate posteriorly in the new genus. In its original concept, Pararhexosa was established by Freeman (1990) for a unique Oriental species, P. flavipalpis , with very large sausage-shaped palpi. Freeman (1990) noted in the original description of the genus that “its relationships are not completely clear cut, but wing venation, large palpi and triangular spiracular sclerite suggest it should be placed near Rhexosa in the Swammerdamellini”. Later, Amorim & Haenni (1997) confirmed this placement and transferred to this genus the Neotropical P. tubifera (Edwards, 1930) (also known from the female only) based on the shape of the palpus and of the anterior spiracular sclerite, and the normally developed abdominal sternites 2-6. Amorim (2007) considered Pararhexosa as the basal genus of the Swammerdamellini and transferred to this genus two Australasian species, P. chelata ( Cook, 1971) and P. senticosa ( Cook, 1971) originally described in Rhexoza ( Cook 1971) , plus two undescribed Neotropical species. He noted, however, that “the placement of these species still does not guarantee a monophyletic genus” ( Amorim, 2007). Despite this restriction, he described the characters of the male [figured for the Australasian P. chelata ( Amorim, 2007: figs 1-3)]. These species share the following characters: anterior spiracular sclerite not elongate and abdominal sternites 2-6 normally sclerotized. However, the palpus of P. senticosa as described by Cook (1971) is short, in contrast with the large, sausage-shaped palpus of the type species of the genus. This and other facts bring some doubt on the congeneric status of the species tentatively added by Amorim (2007). In particular, the Australasian P. chelata and P. senticosa are very probably not congeneric with the type species of Pararhexosa . Although the precise affinities of this genus are very difficult to establish on the basis of female characteristics only, Pararhexosa may possibly be better placed in the vicinity of the genera Pharsoreichertella and Reichertella within the Scatopsini, since it shares several characters with these genera, rather than in Swamerdamellini. The attribution of Neotropical ( Amorim & Haenni, 1997; Amorim, 2007) and Australasian species ( Amorim, 2007) to Pararhexosa seems not well founded according to our present lacunar knowledge. Particularly, the discussion of the position of the genus based on male characters of Australasian or Neotropical species appears untimely. In our opinion, a sound discussion of the position of this genus should await the discovery of males of the type species or of another Oriental species that would be indisputably related to the type species of Pararhexosa . In a wider perspective, the question of the limits between Scatopsini and Swammerdamellini and even of the validity of these tribes is worth asking. On the basis of the points enumerated above and pending a general reconsideration of the Scatopsini and Swammerdamellini, Aztecatopse is for the time being placed within the Scatopsini because the new genus appears to be more closely related to Reichertella and Pharsoreichertella .

The type material of the Nearctic Pharsoreichertella producta ( Cook, 1957) was also examined in the course of this study. The species of Aztecatopse are clearly not congeneric with this species. In Pharsoreichertella the tergite 8 of the female is practically divided into 2 lateral lobes while it is entire, hardly emarginated in the new genus; in the wing, C is long in Pharsoreichertella , reaching 2/3 or even 3/4 of wing length, while it is short, hardly reaching the middle of the wing in Aztecatopse ; the aedeagus is long, simple, unmodified in Pharsoreichertella while it is strongly modified in Aztecatopse . The new genus differs from Reichertella in numerous male and female genital characters: in the male, the general shape of the genital capsule is elongate in the new genus whereas it is much shortened in Reichertella ; the gonocoxites are well developed in the new genus whereas they are not recognizable in Reichertella ; the parameres are elongate in Aztecatopse whereas they are not apparent or short in Reichertella ; in the female, the sternite 8 is more or less deeply divided into a pair of lateral lobes in the new genus whereas it bears a pair of strongly developed valvifers in Reichertella . The shape and development of the pregenital segment in the male and female also strongly differ in both genera.