Syrphoctonus gracilentus (Holmgren, 1858)

Klopfstein, Seraina, 2011, A review of the Diplazontinae of Mongolia (Hymenoptera: Ichneumonidae), Zootaxa 2790, pp. 35-53 : 41-42

Syrphoctonus gracilentus (Holmgren, 1858)

( Fig. 6 )

This species was reported from the Nearctic and Western Palaearctic. It has some very distinctive characters that made Dasch place it in a separate species group together with the Nearctic S. sicarius Dasch, 1964 ( Dasch, 1964a) . An isolated position in the probably paraphyletic genus Syrphoctonus was also supported in a recent phylogenetic analysis of the group (Klopfstein, Kropf, & Quicke, 2010). The most prominent character of the species group is the structure of the tyloids on the antennae of the males. They consist of both the narrow, linear upraising which is the most common tyloid type in the genus, and a bulbous swelling perforated by a large hole dorsad of this ridge ( Fig. 6 ). The SEM investigation revealed abundant pores on the strongly elevated ridge (arrow in Fig. 6 A), a characteristic very similar to tyloids of other representatives of the genus ( Fig. 7 , Syrphoctonus tarsatorius ) (Klopfstein, Quicke, & Kropf, 2010; Steiner, Kropf, Graber, Nentwig, & Klopfstein, 2010). The hole however, a structure not previously examined by SEM, contains branched structures on circular bases that may represent modified hairs ( Fig. 6 B). Further investigations including a sectioning of the involved parts of the antennomeres are needed to clarify whether these structures are sensory or secretory in function. The tyloids in another species, Syrphoctonus tarsatorius (Panzer, 1809) , are connected to internal glands and probably serve as release and spread structures for a contact pheromone during courtship ( Steiner et al., 2010). Judging from the positional and ultrastructural homology of the ridge found in S. gracilentus , the presence of pores and the absence of this structure in the female sex, a similar function can be expected.

Material examined: Mongolia - Central aimak, Ulan-Baator, Bogdoul, 1500–1600m, 21.07.1967 (1ɗ) ( HNHM). Switzerland – GR, Sur, SE Vauastg, Dafora, 1920m, 769.343/154.982, 21.– 28.07.2003, leg. H. Baur (1ɗ) ( NMBE).

Figures

FIGURE 6. Flagellomer 7 of Syrphoctonus gracilentus. A, linear tyloid with small black pores (arrow), and adjacent hole. Scale bar = 50 μm. B, magnification of the hole showing internal structures. Scale bar = 10 μm.

FIGURE 7. Flagellomer 9 of Syrphoctonus tarsatorius. A, linear tyloid. Scale bar = 40 μm. B, magnification showing pores (arrow) on the tyloid. Scale bar = 6 μm.