Tenthredo atra LINNAEUS, 1758

Liston, A. D., Knight, G. T., Heibo, E., Bland, K. P., Barstad, Trond Elling, Blank, S. M., Boeve, J. - L., Fiedler, K., Grearson, K. J., Halstead, A., Jacobs, H. - J., Jansen, E., Lonnve, O., Prous, M., Robinson, J. & Taeger, A., 2012, On Scottish sawflies, with results of the 14 International Sawfly Workshop, in the southern Highlands, 2010 (Hymenoptera, Symphyta), Beiträge Zur Entomologie = Contributions to Entomology 62, pp. 1-68 : 52-54

Tenthredo atra LINNAEUS, 1758

The females are all referable to the form treated under the name var. scopolii Lepeletier in the key by Enslin (1920). They all have a white spot on the metepisternum, but only about half of them have the pronotum narrowly edged with white (in the rest this is completely black). Colour of clypeus varies from nearly completely white to nearly completely black. The orbits are completely black. The males vary not only in the presence or absence of white on the pronotum, but also in the size or presence of a white spot on the metepisternum and the lateral edge of tergum 1.

† Tenthredo ignobilis KLUG, 1817

At Meall nan Tarmachan, 5.vi.2010, two adults were swept from birch, one specimen feeding at catkins of Salix sp. and one visiting inflorescence of Sedum rosea . On 22.vi.2010, most of the adults collected were feeding at inflorescences of Sedum rosea , including one pair in copula.

Variability: the Scottish specimens show little variability in colouration, except that the malar space in the male may be entirely black or marked with white (in females always entirely black).

The following notes outline our provisional conclusions on this newly discovered Scottish member of the Tenthredo atra species group that at present is identified as T. ignobilis . A more thorough study of the taxonomy of the whole species group is evidently needed, but this should ideally be based on material from the entire northern Hemisphere and attempt to clarify not only morphological and genetic taxonomy, but also biological characters (e.g. hostplants). Such a revision falls outside the scope of the present work.

Males of the T. atra group are more uniform in morphology than the females, difficult to distinguish from each other and difficult to associate with females. With few exceptions, described taxa are based exclusively or mainly on female specimens. Before the paper by Lacourt (1992), it had been thought possible that males do not occur at all in some species of the T. atra group (thelytokous parthenogenesis; see particularly comments by Lacourt 1980). In fact, unlike most other genera of Tenthredinidae , no definite case of parthenogenesis has yet been recorded in Tenthredo , currently regarded as by far the largest genus of Symphyta, with over 900 species ( Taeger et al. 2010). Suomalainen (1962) suggested that exclusively parthenogenetic insect species tend to be of relatively recent origin and run a higher risk of extinction than sexually reproducing congeners. Has in the long term this apparent lack of recourse to parthenogenetic reproduction in Tenthredo helped to promote the comparatively high diversity of extant species?

The collections at the RSME, the Hunterian Museum (Glasgow) and Kelvingrove Museum and Art Gallery have been checked, but no specimen of T. ignobilis was found. The species possesses a combination of colour characters that prevent it from running in the key by Benson (1952). It therefore seems that Benson had not seen British specimens.

T. ignobilis , until Chevin (1974) raised it from synonymy, was long treated as a colour polymorphism of T. atra L. Cameron (1882) misinterpreted the description of T. ignobilis and applied the name to a Tenthredopsis species occurring in Britain.

The two existing female syntypes of T. ignobilis (ZMHUB; examined) are regarded as conspecific with the Scottish specimens. The taxonomic significance of apparent slight differences between the Scots specimens and Central European, as compared below, requires further investigation during the course of an in-depth revision of the T. atra group:

- 4 basal serrulae of lancet shorter and lower (Fig. 12). Tegula entirely black. Slightly larger: body length of ♀ ca 13 mm. ... T. ignobilis ( Scotland) .

- 4 basal serrulae of lancet (Fig. 13) longer and higher. Tegula edged with red-brown, or entirely red-brown. Slightly smaller: body length of ♀ ca 11-12 mm. ... T. ignobilis ( Poland (Silesia; syntypes, ZMHUB); lowland-colline zones of Germany, Austria ( SDEI); France ( Alpes Maritimes , 2000 m., leg. C. Schmid-Egger, SDEI)) [Antennal flagellomeres of reared specimens [3 ♀♀ 1 ♂, Austria, Waldviertel, ex Sedum telephium , leg. E. Altenhofer, SDEI] short, but in adults taken in the field, including the types, longer and not different from Scots specimens. The short antennae of the Austrian specimens could be the result of adverse rearing conditions. Alpine specimens exhibit variability in the colour of the rear femora (may be completely red, lacking the usual black dorso-apical streak)] .

T. ignobilis is recorded in Central Europe from N. Italy through to the Netherlands and Poland, but also in Norway and Finland ( Taeger et al. 2006). In eastern Central Europe (e.g. East Germany, northern Austria) it has been recorded mainly at lowland sites, including gardens, attached to Sedum telephium as the larval host ( Pschorn-Walcher & Altenhofer 2006), mainly in regions of low precipitation and high summer temperatures. Taeger (1989) observed that it is “not particularly rare” [translated] in [lowland] south-east Germany. However Chevin (1974) describes T. ignobilis as in France apparently restricted to the Alps.

Only Sedum telephium has so far been recorded as a larval host of T. ignobilis ( Forsius 1918 in Finland, Pschorn-Walcher & Altenhofer 2006 in Austria). According to Forsius (1918), typical T. atra was also reared from S. telephium . S. telephium is a mainly lowland species in Highland Scotland, local except in parts of the west, and is not recorded from Meall nan Tarmachan or Ben Lawers, but is widespread in England ( BSBI 2010). By anology and the circumstances of capture at Meall nan Tarmachan, it seems possible that the host there is Sedum rosea L. (Roseroot), which is abundant on the many crags of this hill. S. album was the only other Sedum species observed to be present in the area, but only on disturbed ground around the dam. The re-visit to the locality on 22.06.2010 by Liston involved lengthy searching of S. rosea for larvae. None was found, nor were any egg pustules detected, that in T. ignobilis are rather conspicuous [obs. Liston; Germany, Brandenburg, Trebnitz [garden] v. 2011]. S. rosea nevertheless seems to be a possible host at Meall nan Tarmachan. Future searches for larvae should be made later in the year, perhaps in mid-July. No association with any plant species was recorded for the specimens from Bridge of Garry and we have not been able to ascertain which Sedum spp. are recorded there (despite particularly the help of M. Robinson).

Our present concept of the British taxa identified hitherto as Tenthredo atra and T. moniliata is summarised in the following key. The key should not be used for continental specimens, where the situation is complicated by apparently greater variability in colour in all taxa [or perhaps additional taxa not yet recognised]. In passing we note as examples just two conspicuous European nominal taxa [several more exist, particularly in the Caucasus] not yet recorded in Britain that will not run cleanly in the key: a female form, at present synonymised with T. atra , with a redbanded abdomen, described by Klug (1817) from Silesia as T. plebeja , and the form or forms with darkened stigma and apex of costa, such as T. nobilis Konow, 1904 (type locality St. Petersburg) sometimes, possibly wrongly, synonymised with T. ignobilis but in several respects more similar to T. moniliata ; see comments by Enslin (1920), who had however, like us, not seen the holotype.

Key to adults of British Tenthredo similar to T. atra : replaces couplet 3(2) in Benson (1952).

1- Stigma and apex of costa of forewing black. ♀: abdomen without red markings; middle serrulae of lancet with rounded teeth. ♂: mesepistermum ventrally completely black; abdomen black with terga 3-5 entirely and more than half of the surface of 2 and 6 red. .... T. atra Linnaeus, 1758 [polyphagous, but possibly a species group containing several sibling species, some of which occur in Britain]

- Stigma and apex of costa of forewing black or brown. ♀: abdomen with red markings on at least abdominal terga (3, 4 and 5 entirely, but occasionally also the extreme apical margins of 2 and base of 6); middle serrulae of lancet entirely flat or with tooth (but if latter then usually smaller and more angular). ♂: mesepistermum ventrally completely black or partly red; either abdomen black with terga 3-5 entirely and less than half of the surface of 2 and 6 red, or terga 2-6 also completely red … 2

2- ♀ (Fig. 11): Stigma and apex of costa of forewing black; pronotum completely black; tegula black. ♂: Mesepistermum ventrally completely black. ... T. ignobilis Klug, 1817 [ Sedum telephium ,? S. rosea . In Britain only one species, but in the West Palaearctic possibly others]

- ♀ (Fig. 13): Stigma and apex of costa of forewing brown; upper edge of pronotum lined with white; tegula red. ♂: Mesepistermum ventrally largely red. ... T. moniliata Klug, 1817 [in the British Isles so far only one species, monophagous on Menyanthes trifoliata , which may or may not be the taxon described by Klug. Throughout the Palaearctic possibly a number of sibling species occurs, perhaps attached to other hostplants]