Rhogogaster

Groups within Rhogogaster

Benson (1965) divided the genus into the following six species groups:

1. For the picta group, Lacourt (1997) created the genus Cytisogaster.

2. The lateraria group includes no European taxa and is not discussed here.

3. Benson’s arctica group consists mainly of species that are placed in Tenthredo today. The former R. arctica Kiaer, 1898 (today known as Tenthredo aaliensis (Strand, 1898)) is the type species of Eurogaster Zirngiebl, 1953. Currently, the species of the Tenthredo mesomela group are also placed in Tenthredo (Eurogaster). This placement is based on the similar shape of mandibles, the shape of the saw, and similar COI-5P barcoding data. Rhogogaster nigrita Mocsáry, 1909, R. vallicola Mocsáry, 1909 (a synonym of T. heros Jakowlew, 1891) and R. virescens (Jakowlew, 1887) in Benson (1965) also belong here. Sciopteryx gilva Konow, 1908, was treated by Benson (1965) as a synonym of R. virescens, and later (Benson 1968) as valid. Its placement in Rhogogaster may be correct, see discussion below.

4. Benson (1965) treated in his opacella group only one species. Rhogogaster opacella sensu Benson is taxonomically ambiguous as the lectotype of R. opacella Mocsáry, 1909 belongs to T. stulta Jakowlew, 1891 (Taeger 2013).

5. The californica group consisted of R. dryas (now treated as a synonym of R. viridis) and R. californica (including R. polaris as its synonym).

6. The viridis group of Benson (1965) comprises nine species, including R. viridis auct. (= R. scalaris), R. chlorosoma, and R. punctulata. These nine species all seem to belong to Rhogogaster. The Asian species of the group need closer scrutiny.

Currently, COI-5P barcodes are available to us only for European and a few Nearctic Rhogogaster. These data correlate more or less clearly with the morphological differences (structure of male genitalia, shape of serrulae, shape and sculpture of mesoscutellum and its appendage, see also the key below).

There are four distinct groups (clusters) for the European species:

1— R. picta, R. chambersi, R. genistae (Benson’s picta group, “ picta group” in Figs 2a –b) 2— R. viridis, R. polaris (Benson’s californica group, “ viridis group” in Figs 2a –b);

3— R. scalaris, R. chlorosoma (a part of Benson’s viridis group, “ scalaris group” in Figs 2a –b); 4— R. punctulata (a part of Benson’s viridis group, “ punctulata group” in Figs 2a –b).

The differences between the barcodes of these clusters are about 8 % or somewhat higher (Fig. 2a). The relationships between these groups remain uncertain, and therefore the same applies to the status of the Cytisogaster (picta group). Only the four groups as listed above are reliably supported by bootstrap values of 90– 99 %. There are some indications that the picta group may be the sister group of the remaining Rhogogaster, but this hypothesis is insufficiently supported (bootstrap values 10–53 %) (Fig. 2 b). We tentatively treat the species of the picta group as a part of Rhogogaster s. l., and the remaining groups as Rhogogaster s. str.

In addition to the special form of the mandibles as described above, the European Rhogogaster s. str. are characterized as follows. It should be noted that this character set does not apply to all Asian species.

a Pterostigma monochrome green, at most very slightly darkened basally (Fig. 1a)

b Temples (postocular area) green (often fading to straw-yellow in dead specimens; exceptionally, live individuals are yellowish, Figs 4a– 4x)

d Tarsi ringed green and black in ♀ (Figs 1b, 1 h, 7h), in ♂ usually black-lined posteriorly

e Clypeus anteriorly more or less roundly emarginated, lateral parts apically more or less serrated, depth of emargination about one third of the length of the clypeus (Figs 1 c, 1d, 7j)

f Body ventrally nearly completely green (Fig. 1b)

g Tips of middle and hind tibial spurs blunt, ± translucent (Figs 1 h, 7h)

h Pronotum in lateral view anteriorly and ventrally without submarginal furrow (Fig. 1 e)