Euura excisa (Thomson, 1863)

Material examined.

Greenland. Narsarsuaq • 2 ♀♀ (TUZ; TUZ 399053, TUZ 109613), 20 June 2025, Prous leg. • 4 ♀♀ (TUZ; TUZ 109614–7), 22 June 2025, Prous leg. • 1 ♀ (SDEI), 22 June 2025, Prous leg. • 1 ♀ (OLC), 22 June 2025, Prous leg. Nuuk • 2 ♀♀ (TUZ; TUZ 399064, TUZ 109618), 26 June 2025, Prous leg. • 7 ♀♀ (TUZ; TUZ 109712–7, TUZ 399099), 3 July 2025, Prous leg. • 17 ♀♀ (OLC; including DEI-GISHym 40557, DEI-GISHym 40558), 3 July 2025, Lønnve & Olsen leg. • 19 ♀♀ (SDEI), 3 July 2025, Liston leg. Kapisillit • 1 larva (TUZ; TUZ 399073), 28 June 2025, Prous leg. • 15 ♀♀ (TUZ; TUZ 109619–29, TUZ 399068, TUZ 399070–1, TUZ 399098), 29 June 2025, Prous leg. • 1 ♀ (OLC), 29 June 2025, Lønnve leg. • 1 ♀ (SDEI), 29 June 2025, Liston leg.

Habitus and variability (Figs 4, 5).

Length 4.0– 5.5 mm. Femora from mostly black to mostly pale; upper head usually completely black, but orbits occasionally brownish; upper rear edge of pronotum sometimes with small pale area. Two specimens from Nuuk (DEI-GISHym 40557, DEI-GISHym 40558) are smaller (Fig. 5), have a somewhat smaller subapical tooth of the claw than most other specimens, and the mesonotum and mesepisternum are shinier.

Habitats.

Favours moist areas, such as snow-patch edges and the banks of streams, and is absent or very scarce in drier places, even when the larval host plant is present.

Host plants and biology.

The only known host is Bistorta vivipara (L.) Delarbre (Prous et al. 2025). Based on some of the larvae found in the field, females might typically lay two eggs per leaf (Fig. 6). No male specimens are known.

Distribution.

Definite records are only from Arctic Europe and Greenland (Smith 1979): principally in tundra but also from open areas in boreal forest regions of Fennoscandia (around 66°N, e. g. Kuusamo Region in Finland and Västerbotten Province in Sweden). The host plant is widespread and abundant in Iceland, but E. excisa has not so far been recorded there.

Genetics.

The COI sequencing of four specimens yielded five different variants (Fig. 7). The dominant variants of the two atypical specimens from Nuuk (DEI-GISHym 40557, 40558) are identical to a specimen from Sweden (SL 69 _ G 1) and 0.4 % different from the typical specimens from Kapisillit and Narsarsuaq. A larva from Kapisillit (TUZ 399073) has a unique sequence that is almost identical (0.2 % different) to a female from Narsarsuaq (TUZ 399053). Curiously, the dominant variant of the Narsarsuaq (TUZ 399053) specimen is identical (1078 bp of COI) to Euura declinata from Estonia (Fig. 7). Two of the specimens (DEI-GISHym 40558, TUZ 399053) also yielded additional variants of COI (one each) that are very similar to the other E. excisa sequences (0.2–0.4 % different).

Comparing nuclear genes (Fig. 8), the atypical specimens from Nuuk (DEI-GISHym 40557, DEI-GISHym 40558) are identical and 0.00–0.08 % different from three Fennoscandian E. excisa (Finland and Sweden, with at least 3425 bp available). The sequenced specimens from Kapisillit and Narsarsuaq (TUZ 399073, TUZ 399053) are identical and 0.11–0.43 % different from all the other specimens (Nuuk and Fennoscandia). The atypical specimens from Nuuk are much more heterozygous (possess distinct haplotypes for five nuclear genes out of seven) compared to the specimens from Kapisillit (two nuclear genes out of seven with two haplotypes) and Narsarsuaq (all five sequenced nuclear genes homozygous). The haplotypes of the Nuuk specimens are very similar to the haplotypes of Fennoscandian specimens, hence the higher similarity between them in distance calculations compared to the specimens from Kapisillit and Narsarsuaq.