Homotropus Förster 1869,

Klopfstein, Seraina, 2014, Revision of the Western Palaearctic Diplazontinae (Hymenoptera, Ichneumonidae), Zootaxa 3801 (1), pp. 1-143: 58-59

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Homotropus Förster 1869


Homotropus Förster 1869 

Type species. Bassus elegans Gravenhorst 1829 

Diagnosis. The genus Homotropus  currently includes morphologically rather divergent species, which is reflected by the fact that it keys out at several couplets in the genus key. Many species, especially those that lack a fore wing areolet, can be mistaken for Syrphoctonus  species. Homotropus  species, however, have a complete epicnemial carina, the spiracle of the third tergite usually distinctly above the lateral fold, and a distinctive clypeus. Males can be confounded with Phthorima  or Bioblapsis  ; see those generic accounts for diagnostic features. I tried to account in the species keys for specimens of these genera that might be difficult to place.

Face coriaceous and matt, without vertical impressions, in females entirely black or with a yellow central patch, in males entirely yellow or black with yellow inner orbits and a yellow central patch. Clypeus usually with apical margin thin, impressed along margin, resulting in central area being convex. Antenna with apical flagellomeres usually longer than wide, in males always with tyloids which in most species are linear and narrow ( Fig. 13View FIGURE 13. A H; exceptions: H. tauriscorium  and H. venustus  ), without long setae. Mesoscutum without notauli; sculpture various, ranging from entirely smooth and shining, with or without punctures, to being strongly coriaceous and matt; yellow shoulder marks present or absent, their inner corners sometimes extended into two parallel lines on mesoscutum; mesopleuron sometimes entirely smooth and shining but often with punctures and / or coriaceous sculpture at least on lower half; epicnemial carina complete ventrally. Propodeum various, sometimes with a full set of carinae enclosing basal, petiolar and lateral areas but usually with carinae partly or fully reduced; propodeal spiracle inconspicuous; scutellum only carinate basally. Fore wing areolet sometimes absent but usually present, in which case vein 3 rs-m often interrupted or unpigmented; hind wing with 2–4 basal hamuli. Hind tibia various, orange, yellow, or white with a dark apex and subbasal spot, very rarely ( H. venustus  ) even black-white-black banded. Female metasoma usually evenly tapered to apex, sometimes strongly compressed posterior to third segment but never with hind margins of the tergites concave; tergites without transverse impressions. First tergite usually without median dorsal carinae, but if present, they converge over basal half and are parallel and widely separated on apical half. Second tergite with spiracle dorsal, above lateral fold, third tergite with spiracle usually above but rarely below or behind the fold. Metasoma black, sometimes with yellow markings, or marked with orange. Ovipositor sheaths 0.3 times as long as hind tibia, either parallel-sided and fully enclosing ovipositor or tapered and diagonally truncate; with inconspicuous setae ventrally and apically. Males with tergites 9 and 10 as separate sclerites, sternite 9 about two times wider than long, emarginated apically, thus forming two lobes, their outer corners rounded.

Phylogeny. Homotropus  is the largest genus of the Syrphoctonus  genus group and includes most of the species previously included in Syrphoctonus  , although the non-European species have not been properly placed yet. The name Homotropus  has recently been re-invoked for these species because phylogenetic studies suggest that the tarsatorius  and laevis species groups (as defined by Dasch 1964) should be removed from this genus in order to restore its monophyly (Klopfstein et al. 2011). The exact limits of the genus Homotropus  remain unclear from the phylogenetic analyses and more extensive species sampling is needed in order to clarify the relationships, especially of the species crassicornis  and vitreus  relative to the genera Bioblapsis  and Phthormia. I here adopt a conservative approach and leave them in this genus until further evidence is available.

Distribution. Worldwide. After checking the non-European species currently grouped in Syrphoctonus  , most of them will probably be transferred to Homotropus  , which will then probably become the largest genus of the subfamily.

Biology. A number of host records are available for the more common species, and indicate that the genus parasitizes on Syrphinae  and that several species are generalists.

Notes. I refrain from splitting the genus into species groups as done by Dasch (1964 a) because their circumscription is partly unclear and several species could not be placed. Only a phylogenetic study with a dense taxon sampling is suited for erecting such groupings. When I mention species groups, I thus loosely refer to Dasch’s circumscriptions.