Systoechus laevifrons (Loew, 1855)

Pohjoismäki, Jaakko & Kahanpää, Jere, 2022, Systoechus laevifrons (Loew, 1855) new to Finland and the Western Palearctic region (Diptera, Bombyliidae), Norwegian Journal of Entomology 69, pp. 51-61 : 54

Identification of Systoechus laevifrons from Finland

During a visit to Säkylänharju (61.011°N, 22.549°E), south-western Finland on 21.VI.2021, the authors of this paper were looking for the species that was, at the time, thought to be Systoechus gradatus . In the recent years the species have been observed rarely and only in single individuals in Finland. However, in 2021 dozens of individuals were observed and some were collected by hand netting for reference purposes. When examining the specimens, author JP noted that they differed markedly from the S. gradatus material he had collected in France and Greece. The Finnish specimens are notably larger (9–11 mm) than the southern European ones (<8 mm) and they had a black frons covered predominantly with long black bristles ( Figure 1A–F ). The male specimens were not identifiable with the old Palearctic key ( Engel 1937), but the females were easily determined as Systoechus laevifrons (Loew) due to the characteristic frontal calluses ( Figure 1D ), not present in any other Palearctic Systoechus species. The male of S. laevifrons was unknown at the time of writing of the Engel (1937), but it is included in the identification keys to the Bombyliidae of Russian Far East ( Zaitzev 2004).

As the Finnish records are far outside the previously known distribution range of S. laevifrons , the Finnish specimens were compared with S. laevifrons collected from the Russian Far East. No notable morphological differences between the specimens were observed. Furthermore, we were successful in obtaining full Co1 DNA barcode sequences from both Finnish and Russian specimens. The DNA barcode sequences of the S. laevifrons specimens were almost identical and also distinct from the sequences of all other Systoechus species available in the Barcode of Life Database (BOLD) ( Figure 2 ). It is noteworthy that the northern Nearctic species of Systoechus are more closely related to Systoechus laevifrons than any European species included in the analysis. Curiously, all the Co1 barcodes available in BOLD for S. candidulus and S. vulgaris are very similar and share the same BIN. The two species are apparently distinguished from the colour of the facial setuale ( Hall & Evenhuis 1981); the species pair might deserve a more detailed analysis.

Figures

FIGURE 1. Systoechus spp. (A) Habitus of male Systoechus laevifrons (Loew, 1855). Finland, Säkylänharju, 20.VI 2021. J. Pohjoismäki leg. BOLD sample ID JP-A2021-003 (B) Male S. gradatus (Wiedemann in Meigen, 1820). France, Flassans-sur-Issole, 10.VII.2011. J. Pohjoismäki leg. BOLD sample ID JP-A2021-002. (C) S. laevifrons male (same specimen as in A) and (D) female (Finland, Säkylänharju, 20.VI.2021. I. Kakko leg) head in dorsal view. (E) S. gradatus male and (F) female head (both France, Flassans-sur-Issole, 10.VII.2011. J. Pohjoismäki leg.)

FIGURE 2. Co1 sequence maximum-likelihood phylogenetic tree of Systoechus and Bombylius species. BOLD sample ID number is given for each specimen.