Syrphoctonus venustus (Dasch, 1964)

Klopfstein, Seraina, 2011, A review of the Diplazontinae of Mongolia (Hymenoptera: Ichneumonidae), Zootaxa 2790, pp. 35-53 : 45-52

Syrphoctonus venustus (Dasch, 1964)

( Fig. 8 )

I compared the males reported by Momoi as “ Homotropus species 1” and “species 2” from Central aimak (Table 1) to the holotype (female) and to a paratype (male) of Syrphoctonus venustus . This species was described by Dasch from North America and placed in an own species group because of its distinctiveness ( Dasch, 1964a). The seven males from Mongolia belong to the same species, but show a larger morphological variation than reported by Dasch from the small number of specimens he examined. I here redescribe the male of S. venustus to take the Mongolian specimens into account.

Material examined. Mongolia - Central aimak, SE of Somon Bajanzogt, 1600m, 11.06.1966 (6ɗ); Central aimak, Ulan-Baator, left border of Tola, 1300–1400m, 31.05.1967 (1ɗ) (all HNHM). USA – (holotype) Idaho, Hollister, 23.10.1930 (1Ψ) ( USNM Washington); (paratype) Utah, Strawberry Daniel Pass, 19.06.1948 (1ɗ) (Townes Collection, Gainesville).

Diagnosis. Syrphoctonus venustus is in some respects similar to S. elegans (Gravenhorst, 1829) or S. nigritarsus (Gravenhorst, 1829) , e.g. by the punctuation of the thorax and the coloration of the face in the male. The unique modifications of the parameres, the distinctive clypeus and especially the shape and ultrastructure of the tyloids however support that Syrphoctonus venustus belongs to a separate species group, in which it was placed by Dasch (1964a).

Description of the male. Fore wing length 3 to 4.2 mm; head irregularly coriaceous, but with some smooth and shining areas on the central face and / or close to the eye margins, with punctures that range from being distinct to indistinct; face protruding below antennal scrobes; clypeus with a weak to strong median emargination, often smooth and shining and with longitudinal carinulae; upper tooth of mandible shallowly bidentate; 17 or 18 flagellomeres, with tyloids on segments 6 or 7 to 13 or 14. The tyloids of this species are unique ( Fig. 8 ), spanning the whole length of the median antennomeres as seen in all members of this genus, but being broadly lenticular in shape. Their surface is covered with irregular, shallow depressions and with pores that probably act as release structures for glands. Mesoscutum polished and punctate, with punctuation less distinct on the sides, notauli absent; mesopleurum and metapleurum polished with punctuation less distinct on upper half, sternaulus shallow, prepectal carina complete; propodeum coriaceous to rugulous, lateral carinae indicated to absent. Fore wing with areolet open or closed (closed in three of the seven specimens, although in two of them only on one fore wing), 2–3 hamuli on costellan fold of hind wing. Petiole rectangular, 1.2–1.4 times longer than wide, lacking submedian carinae; tergites coriaceous, often with sparse punctures, smooth and shining from tergite 5 or 6 onwards; parameres bearing thickened hairs on apical margin.

Colouration of the male. Black; yellow on clypeus, mandible, palpi, median facial spot, orbital bar widened ventrally, sometimes patially touching median facial spot, scape and pedicel ventrally, flagellum lighter ventrally. Mesoscutum with yellow shoulder marks, yellow on tip of probotal lobe, spot under each wing, tegula, scutellum either all black or with yellow spots on anterior corners and apically. Coxae black at base, yellow on apex, trochanters black and yellow, femora red, often marked with black ventrally, sometimes whole hind femur darkened. Tibiae orange, hind tibia white with a subbasal and apical brown band or spot. Metasoma all black to black with red on front margin or all of tergite 3 and hind margins of tergites 4 to 6.

Figures

FIGURE 8. Antennomeres of Syrphoctonus venustus. A, oval tyloids on flagellomeres 8 and 9. Scale bar = 100 μm. B, magnification showing pores (arrow) and shallow depressions. Scale bar = 20 μm.