Syrphoctonus Förster 1869

Klopfstein, Seraina, 2014, Revision of the Western Palaearctic Diplazontinae (Hymenoptera, Ichneumonidae), Zootaxa 3801 (1), pp. 1-143 : 93-95

Syrphoctonus Förster 1869

Type species. Bassus exsultans Gravenhorst 1829

Recently, this genus was restricted to include only the tarsatorius and laevis species groups as defined by Dasch (1964a), based on a large morphological and molecular analysis of the subfamily ( Klopfstein et al. 2010a; Klopfstein et al. 2011). Other species previously included with in Syrphoctonus are now referred to the genera Homotropus and Fossatyloides.

Diagnosis. Syrphoctonus species are most similar to some Homotropus species and some females might also be confounded with Woldstedtius . From Homotropus , most Syrphoctonus species can readily be identified by the position of the spiracle of the third tergite on the laterotergite or level with the fold separating it from the dorsal part, the usually interrupted epicnemial carina, the lack of a fore wing areolet, and by the shape of the clypeus. Some of these characters, however, are subject to variation, sometimes even intra-specifically. I tried to account for any such difficulties by providing cross-references in the species keys. From Woldstedtius , females of Syrphoctonus can be identified by the shape of the ovipositor sheaths and usually the colouration of the hind tibia.

Face coriaceous and matt, without vertical impressions, in females entirely black or with a yellow central patch, in males entirely yellow. Clypeus with apical margin thin, with a basal elevation and impressed only laterally, resulting in the central area being convex and the sides being concave. Antenna with apical flagellomeres longer than wide, in males with linear, narrow tyloids, without long setae. Mesoscutum without notauli; coriaceous and matt with inconspicuous but sometimes dense punctures; yellow shoulder marks usually present; mesopleuron either entirely coriaceous and matt or rather smooth, especially on upper half, never strongly punctate; epicnemial carina interrupted behind fore coxae. Propodeum with carinae reduced, at most with some traces of lateral carinae; propodeal spiracle inconspicuous; scutellum only carinate basally. Fore wing areolet absent, although very rarely present as an aberration in S. tarsatorius ; hind wing with 2–3 basal hamuli. Hind tibia white, yellow or orange with apex dark. Female metasoma evenly tapered to apex; tergites without transverse impressions. First tergite without median dorsal carinae. Second tergite with spiracle dorsal, above lateral fold, third tergite with spiracle below or behind the fold. Metasoma black, often with yellow apical bands on most tergites, or orange on median tergites. Ovipositor sheaths 0.3 times as long as hind tibia, rather stout, laterally compressed, slightly tapered and fully enclosing ovipositor or 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. Syrphoctonus is placed as the most basal genus of the Syrphoctonus genus group, followed by the genera Woldstedtius , Enizemum , and finally Homotropus and related genera. Its monophyly is supported by some rather vague morphological characters such as the reduction of the epicnemial carina, which is very distinct in some but less so in other species (see keys and species descriptions). Molecular characters clearly support the monophyly of this genus, but only five species were included in these analyses ( Klopfstein et al. 2010a; Klopfstein et al. 2011).

Distribution. Probably Holarctic. Most of the non-European species currently known under this genus have not been compared to the new concept of Syrphoctonus , and might be transferred to the genus Homotropus in the near future.

Biology. Host records of S. tarsatorius and S. fissorius indicate that these are polyphagous species which attack a variety of host genera. They have been reared most frequently from abundant host species of the genera Epistrophe , Syrphus and Episyrphus ( Schneider 1950; Rotheray 1981b; Fitton & Rotheray 1982; Rotheray 1984).

Notes. The use of the names Syrphoctonus , Homotropus and Woldstedtius differed between authors in the past. While Förster (1869) had already distinguished between the genera Syrphoctonus and Homotropus , later authors combined the two entities under a single name, which for a long time was Homocidus Morley (Morley 1914 ; Schmiedeknecht 1926; Uchida 1930). Beirne (1941) then even combined the species of these genera with most other diplazontines under Diplazon . Dasch (1964a) combined the species of Syrphoctonus and Homotropus under the latter name, and used the name Syrphoctonus for the genus now known as Woldstedtius . As the type species of Syrphoctonus is Bassus exsultans Gravenhorst , a junior synonym of S. tarsatorius , the genus combining the Homotropus and Syrphoctonus species was later referred to under this name. After the genus was split ( Klopfstein et al. 2011), both Syrphoctonus and Homotropus became valid again.

Key to species

1. Hind coxa red or yellow................................................................................ 2

- Hind coxa black, at least basally.......................................................................... 3

2. Epicnemial carina indistinct on mesosternum, only present laterally. Metasoma black, tergites often with yellow hind margins, first tergite as long as or shorter than wide. In females, metasoma dorsoventrally depressed to gradually tapered..................................................................................... Syrphoctonus tarsatorius (Panzer)

- Epicnemial carina fully developed. Metasoma usually orange on tergites 2 and 3, first tergite longer than wide. In females, metasoma usually laterally compressed posterior to fourth segment............... cf. Homotropus signatus (Gravenhorst)

3. Scutellum black....................................................................................... 4

- Scutellum marked with yellow........................................................................... 6

4. Clypeus more than 2.5 times broader than high, smooth and polished, with apical lobes very weakly developed. Mesoscutum distinctly punctate, the punctures separated by less than their diameter, on a more or less smooth background, mespleuron weakly punctate at least along anterior margin. Metasoma black with yellow spots on posterior corners of tergite 3 in females and 3 or 4 to 5 in males....................................................... Syrphoctonus borealis Holmgren

- Clypeus usually about 1.5–2.0 times broader than high, with some coriaceous sculpture and apical lobes well developed. Mesoscutum mostly coriacesous and matt, punctures usually weak and rather sparse. Metasoma either entirely black, marked with orange, or with yellow spots on basal corners of some tergites, or with narrow yellow hind margins................ 5

5. Epicnemial carina broadly interrupted on mesosternum, only present laterally. Metasoma black. Hind tibia white or yellow with a dark apex. Mesosoma evenly shiny-coriaceous. First tergite as long as or shorter than wide.. Syrphoctonus idari Diller

- Epicnemial carina fully developed. Metasoma usually orange on tergites 2 and 3. Hind tibia uniformly orange. Mesosoma with irregular sculpture, often coriaceous only on lower half of mesopleuron. First tergite longer than wide........................................................................................ cf. Homotropus signatus (Gravenhorst)

6. Scutellum yellow or with a yellow apical spot. Metasoma usually orange on tergites 2 and 3 and with yellow posterior bands on tergites 2–5, especially in males. Male antenna with tyloids on flagellomeres 7–14... Syrphoctonus desvignesii ( Marshall)

- Scutellum with a yellow margin, black centrally. Metasoma black, in males with two yellow spots on basal corners of tergite 3. Male antenna with tyloids on flagellomeres 2 to 10 or 11......................... Syrphoctonus fissorius (Gravenhorst)