Oscinella Becker, 1909

Riccardi, Paula Raile & Hartop, Emily, 2024, Large-scale integrative taxonomy of Swedish grass flies (Diptera, Chloropidae) reveals hitherto unknown complexity of a dark taxon, Zoologica Scripta 53 (5), pp. 614-631 : 624-626

4.2.6 | Genus Oscinella Becker, 1909

There are 23 species of Oscinella Becker in the Palearctic region (von Tschirnhaus pers. comm.). Although this genus is fairly abundant across Europe, encompasses agricultural pests within the O. frit complex ( Nartshuk & Andersson, 2013) and are addressed in thousands of publications, a taxonomic revision of its Palearctic species is still pending. Nielsen (2014) established four criteria to identify species of O. frit complex from Denmark.

In our dataset, 13 species of Oscinella were recognised, all originally grouped into a single molecular cluster (Figure 6). As expected, this cluster posed several challenges, not only for the O. frit species complex described in the literature ( Nartshuk & Andersson, 2013). Seven of the 13 species were separated reclustering at a 3% threshold ( O. maura (Fállen) , O.pusila (Meigen) , O. vindicata (Meigen) , O. frit var. 1, O. frit var. 2, O. frit var. 5 and O. cf. cariciphila Collin ). However, the genetic boundaries between the other six species were less clear, with O. angularis and O. nitidissima (Meigen) sharing the same haplotype.

For the remaining four species of Oscinella , O.frit var. 3 and O. frit var. 6 were split at a 0.96% threshold. The only haplotype assigned to O. cf. nigerrima (Macquart) and the five haplotypes of O. frit var. 4 were studied in detail. Despite the male terminalia morphology being a useful tool for species recognition within Chloropidae , small variations in the surstylus width and pilosity, cercus shape and surface and phallic complex among the five haplotypes verified were not conclusive for establishing reliable species boundaries within O. frit var. 4. Certainly, additional genomic markers allied to three-dimensional imaging techniques of complex morphological features can provide additional evidence for resolving further the Oscinella frit species conundrum. The diagnostic features of the Oscinella species are outlined in Table 3.

The above criteria related to the gena width, arista ratio and tibia colour proposed by Nielsen (2014) were less informative than the femoral organ and male terminalia to identify the species from the O. frit complex. Additionally, the species O. frit var. 2 have the fore femur notably enlarged as a diagnostic feature. Although the species O. frit . var. 5 and var. 6 share the femoral organ covered with spine-like setulae, there are differences in the ocellar triangle length and setulae coverage. Furthermore, they did not appear as directly related in the haplotype network; therefore, they were considered as separate species.

4.3 | Distribution