Identification key to the Finnish species of Pipizella, with addition of P. virens known from neighbouring countries.

1. Males.................................................................................................................................................. 2

– Females ............................................................................................................................................. 5

2. Basotarsomere of front tarsus distinctly yellow. Surstylus (in blue colour) in lateral view widely oval, widest in apical half (Fig. 7A) .......................................................... Pipicella certa Violovitsh, 1981

– Basotarsomere of front tarsus dorsally brown and ventrally brownish yellow. Surstylus (in blue colour) in lateral view widest at base, usually gradually tapering towards apex (Figs 8B, 9B, 10B)3

3. Surstylus with wide base and very narrow apex in lateral view (van Steenis & Lucas 2011: fig. 169). Post-anal hood small, rectangular (van Steenis & Lucas 2011: fig. 168)............................................ ........................................................................................................ Pipizella virens (Fabricius, 1805)

– Surstylus (in blue colour) tapering gradually in lateral view (Figs 8B, 9B, 10B). Post-anal hood (in red colour) large or apically rounded (Figs 8C, 9C, 10C)................................................................. 4

4. Inner median flange of hypandrium narrow (in red colour) basally broadest, evenly tapering (Figs 8B, 9B). Post-anal hood (in red colour) usually apically almost straight (Figs 8C, 9C) ............................................................................... Pipizella obscura van Steenis & Lucas, 2011

– Inner median flange of hypandrium (in red colour) evenly broad, not basally broadest (Fig. 10B). Post-anal hood (in red colour) apically rounded (Fig. 10C)........ Pipizella viduata, (Linnaeus, 1758)

5. Longest hairs on anterior side of hind tibia about twice diameter of tibia, as in males (van Steenis & Lucas 2011: fig. 167) ...................................................................... Pipizella virens (Fabricius, 1805)

– Longest hairs on anterior side of hind tibia less than 1.5 times diameter of tibia (Figs 11A, 11B, 11C).................................................................................................................................................... 6

6. Basotarsomere of front tarsus entirely and distinctly yellow (Fig. 12A). … Pipizella certa Violovitsh, 1981

– Basotarsomere of front tarsus dorsally brown and ventrally brownish yellow (Figs 12B, 12C) ...... 5

7. Ratio T4WL is less than 1.20....................................... Pipizella obscura van Steenis & Lucas, 2011

– Ratio T4WL is more than 1.30 ..................................................... Pipizella viduata (Linnaeus, 1758)

Observations of one additional Pipizella species, Pipizella virens (Fabricius, 1805), are known from the neighbouring countries to Finland. The species is reported from Sweden (SLU 2024, GBIF 2024) and from Estonia (GBIF 2024), and it thus appears possible to find P. virens also from Finland. Both sexes of P. virens have the longest hairs on the anterior side of the hind tibia which is up to twice as long as wide, whereas the Pipizella species known from Finland have the longest hairs on the anterior side of the hind tibia at most 1.5 times as wide as the tibia. In the male genitalia the lateral view of the surstylus of P. virens male shows a long narrow apical part and the lower gonocercus is shaped as a bifid plate (T-shaped) (Verlinden 1999: 20) which differentiates it from the Pipizella species known from Finland in which these structures are different (Figs 7–10; Haarto & Kerppola 2007; Bartsch et al. 2009; van Steenis & Lucas 2011; Bot & Van de Meutter 2023).

Molecular study

The final COI barcode data matrix comprised 24 COI barcodes of Pipizella specimens in total, of which 16 were newly generated for this study (Table 1).

The morphological identifications of the unknown female sexes were supported by the generated DNA barcodes, which linked the included male and female samples of the focal species Pipizella certa, P. obscura and P. viduata in independent clusters as visualized in the Neighbor-Joining tree (Fig. 13). The uncorrected pairwise COI barcode sequence divergences between Pipizella obscura and P. viduata is 0.16%, between P. certa and P. viduata it ranges between 1.3–1.7%, and between P. obscura and P. certa between 1.2–1.9%.