Archimicrodon Hull

Reemer, Menno & Stahls, Gunilla, 2013, Generic revision and species classification of the Microdontinae (Diptera, Syrphidae), ZooKeys 288, pp. 1-213 : 17-19

Archimicrodon Hull Figs 7-26

Archimicrodon Hull, 1945: 75. Type species: Microdon digitator Hull, 1937: 19, by original designation.

Hovamicrodon (Subgenus) Keiser, 1971: 248. Type species: Hovamicrodon silvester Keiser, 1971: 251, by original designation. stat. n.

Description.

Body length: 4-11 mm. Small to moderately sized flies with short antennae and oval abdomen. Head about as wide as thorax or slightly wider. Face convex; narrower than an eye. Lateral oral margins not produced. Vertex flat. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male strongly converging at level of frons, with mutual distance about as large as width of antennal fossa. Antennal fossa about as wide as high. Antenna shorter than distance between antennal fossa and anterior oral margin; basoflagellomere as long as or longer than scape, oval, sometimes with acute apex and concave dorsal margin; bare. Postpronotum pilose. Scutellum semicircular; with or without calcars, sometimes apicomedially sulcate; in subgenus Hovamicrodon calcars are spatulate (spoon-shaped). Anepisternum weakly sulcate; pilose anteriorly and posteriorly, widely bare in between. Anepimeron entirely pilose. Katepimeron convex; bare. Wing: vein R4+5 with or without posterior appendix (this appendix only lacks in certain undescribed species from New Guinea); vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular, with small appendix; crossvein r-m located around basal 1/5 to 1/4 of cell dm. Abdomen oval, about 1.5 to 2 times as long as wide. Tergites 3 and 4 fused. Sternite 1 pilose or bare. Male genitalia: phallus furcate, with furcation point near apex; hypandrium with basal part bulb-like; epandrium without ventrolateral ridge; surstylus unfurcate.

Diagnosis.

Abdomen oval. Antenna shorter than distance between antennal fossa and anterior oral margin. Postpronotum pilose. Postero-apical corner of cell r4+5 rectangular. Proepimeron bare. Anepisternum widely bare medially, also on dorsal half. Anepimeron entirely pilose. Vein R4+5 usually with posterior appendix; if not: thorax and abdomen entirely black.

Discussion.

Archimicrodon was described as a subgenus of Microdon by Hull (1945), and considered as such by subsequent authors, including Cheng and Thompson (2005), who stated that three species are included. Most of the species assigned to Archimicrodon in the present paper were previously placed in Microdon . However, they do not agree with the more strict definition of Microdon used here. Its independent position from Microdon and its monophyly are supported by the phylogenetic results of Reemer and Ståhls (in press). These are reasons to raise Archimicrodon to generic status.

Three groups are recognized within this genus: Archimicrodon s.s., the subgenus Hovamicrodon , and a ‘leftover’ group, here called Archmicrodon s.l. Archmicrodon s.s. is based on Archmicrodon simplicicornis (de Meijere, 1908), a subjective senior synonym of the type species of the genus, Microdon digitator Hull, 1937 syn. n. Archimicrodon s.s. is here defined by the shape of the surstylus: more or less oval, without a long posterior process (Fig 9, 15); scutellar calcars are either present or absent, but never spatulate. The subgenus Hovamicrodon is defined (following Keiser 1971) by the spatulate shape of the scutellar calcars (Fig. 18); the surstylus has a long posterior process (Fig. 19). Archimicrodon s.l. is here defined as containing all other species, in which the scutellar calcars are absent or - if present - not spatulate, and in which the surstylus has a long posterior process (Figs 22-26). As far as the African species are concerned, this group corresponds with the brevicornis-group of Bezzi (1915).

The three groups are very similar in their morphology, except for the small differences as noted above. It seems likely that the groups are closely related. The subgenus Hovamicrodon is probably monophyletic, considering the spatulate scutellar calcars in combination with its restricted distribution (Madagascar). However, as the phylogenetic analyses by Reemer and Ståhls (in press) indicate, it is so closely related to Archimicrodon s.l. (which is recovered as paraphyletic with respect to Hovamicrodon ) that a separate generic status seems not warranted. Besides, a spatulate shape of the scutellar calcars can also be found in certain species of the New World genera Laetodon gen. n. and Serichlamys Curran, 1925. The latter genus is recovered as sister to Archimicrodon by Reemer and Ståhls (in press). As this character is not unique, it does not provide sufficient basis to base a genus on.

Sexual dimorphism can be pronounced, especially in the African species of this group (including Hovamicrodon ). Females tend to be much larger than males, and are different in colouration (usually darker). As several species were described from one sex only (such as certain Madagascar species described by Keiser 1971), it is possible that some of these species are actually synonyms. However, as many taxa are represented by only one specimen, these matters cannot yet be resolved.

Hova is the name of one of the social castes of the Merina, an ethnic group indigenous to Madagascar. Keiser (1971) used this name for his genus Hovamicrodon . Surprisingly, he did not include the Madagascar species Microdon hova Hervé-Bazin, 1913 in this genus, although this species clearly belongs to this group (spatulate scutellar calcars). Keiser (1971) does mention a specimen which he believes to be Microdon hova , based on the description, but for some reason this species is not listed under Hovamicrodon . However, when Keiser died in 1969, his paper was not finished yet. It was published posthumously, after the manuscript was finished and submitted by E. Lindner. Therefore, it is seems possible that Keiser intended to include Microdon hova in Hovamicrodon .

Notes on species.

In genitalia, Microdon browni Thompson, 1968 is similar to Archimicrodon s.l.: phallus short, apically furcate, with dorsobasal projection; hypandrium with bulb-like base; surstylus with two elongate lobes; epandrium without ventrolateral ridge. In external morphology, the only difference with Archimicrodon seems to be that the antennae are longer than the distance between the antennal fossa and the anterior oral margin. This character is considered not important enough for group definition, as antennal length is quite variable within many genera of Microdontinae . For these reasons, Microdon browni is here considered as a species of Archimicrodon s.l. The phylogenetic analysis of morphological characters by Reemer and Ståhls (in press) provides no further clue to the taxonomic affinities of this taxon.

Diversity and distribution.

Described species: 45. Widely distributed in the Afrotropical, Oriental and Australasian regions, with one species known from the Eastern Palaearctic ( Archimicrodon simplex (Shiraki, 1930)). Archimicrodon s.s. is only known from the Oriental region. The number of species of Archimicrodon s.s. is not known, as the male genitalia of several species were not studied. The subgenus Hovamicrodon (six species) is restricted to Madagascar.