Stenocephus janseni, Liston & Prous, 2021

Liston, Andrew & Prous, Marko, 2021, Stenocephus janseni sp. nov., a new species of stem-sawfly from Germany (Hymenoptera: Cephidae), Acta Entomologica Musei Nationalis Pragae 61 (1), pp. 73-81 : 78-80

Stenocephus janseni sp. nov.

Type material examined. Hඈඅඈඍඒඉൾ: ♀ (DEI-GISHym84482), ‘ Germany: Brandenburg, Müncheberg 4 km NW, 52.521°N 14.064°E [58 m a.s.l. in woodland beside railway track “Ostbahn”; Berlin to Kostryn], 20.V.2020, leg. A. Liston, M. Prous’ [white label, printed], ‘ Holotype ♀ Stenocephus janseni n. sp. det. A. Liston’ [red label, handwritten], ‘DEI- GISHym84482’ [white label, printed]. Deposited in the Senckenberg Deutsches Entomologisches Institut, Müncheberg.

Description. Female ( Figs 1–17 ). Length: 10 mm, without ovipositor.

Colour ( Fig. 1 ). Black. Parapterum whitish. Yellow -brown are: extreme dorsal apex of profemur, all tibiae, more or less all tarsi except for distally progressively somewhat darker tarsomeres (from apex of basitarsomere), abdominal terga 3 and 4 and corresponding sterna, and tergum 2 with corresponding sternum except for their more or less fuscous dorsal / ventral parts. Wing membrane subhyaline. Venation basally yellowish, apically (including pterostigma) becoming brown.

Head in dorsal view ( Fig. 2 ) slightly contracted behind eyes; lateral length (from anterior of eye to most posterior point) approximately 0.5× width. Temple much shorter than length of eye ( Fig. 4 ). Genal carina developed from malar space to about 0.33 height of eye. Ratio of distance between inner edges of toruli: distance between lower edge of torulus and centre of anterior tentorial pit approx. 1.2: 1.0 ( Fig. 3 ). Postocellar area rather densely punctured, with shiny interspaces ( Fig. 2 ). Frontal area more densely and finely punctured; dull ( Fig. 3 ). Vertex, temple and supraclypeal area shiny, with weak, scattered punctures. Left mandible ( Fig. 15 ) outer (anterior) tooth longer than the inner; inner and outer teeth of about equal basal width; inner tooth anterior edge slightly convex; posterior edge concave. Labial palp with four palpomeres, much shorter than maxillary palp. Apical labial palpomere much wider than apical maxillary palpomeres. Maxillary palp ( Fig. 14 ): palpomere 6 arising at approximately 0.6 of length of 5 (from base); palpomeres 5 and 6 combined length slightly less than 4 (or palpomere 4 about 1.5× as long as 6). Antenna ( Fig. 16 ) long and slender; about as long as combined length of fore wing costa and stigma; 28 antennomeres. Flagellum widest at about 0.75 from base, gently expanding from apex of flagellomere 3. Flagellomere 1 slightly longer than 2 (1.2: 1.0). All flagellomeres longer than broad. Pubescence on upper head about 0.25× as long as diameter of anterior ocellus, and sparser than on thorax.

Most of thorax ( Figs 5–8 ) deeply punctured, with narrow interspaces, and dull. Dorsal part of propleuron glabrous and without punctures ( Fig. 7 ). Longest setae on thorax about 0.5× as long as diameter of anterior ocellus. Pronotum in dorsal view ( Fig. 6 ) slightly wider than long (ca. 1.1: 1.0); anteriorly and posteriorly strongly carinate on dorsal margins; a longitudinal furrow present, deeper and wider posteriorly, ending posteriorly in a shallow marginal notch and anteriorly in a small triangular area without punctures or sculpture. Mesoscutellum almost circular in outline in dorsal view ( Fig. 8 ). Protibia without preapical spurs; mesotibia with one preapical spur; metatibia with two preapical spurs ( Fig. 10 ). Metatibial preapical spurs longer than apical ones ( Fig. 10 ). Metatarsomere 1 slightly longer than combined lengths of 2–4 (1.03: 1.00). Claw with inner tooth close to outer tooth and clearly larger; no basal lobe ( Fig. 9 ). Fore wing stigma 8.6× as long as broad. Fore wing anal cell with cross-vein. Cross-vein 3r-m present in hind wing; 7 hamuli on hind wing.

Abdominal terga shallowly and indistinctly punctate; shiny between the punctures. Tergum 1 with a complete longitudinal median incision extending anteriorly. Tergum 2 in lateral view ( Fig. 11 ) strongly widened towards posterior (distal height approx. 1.25× length). Terga 3–7 progressively widened distally ( Fig. 1 ). Cerci short ( Figs 12 , 13 ): appearing about 0.15× as long as valvula 3 in dorsal view ( Fig. 12 ). Valvifer 2 about as long as valvula 3. In lateral view upper edge of valvula 3 with straight profile; longitudinally with a ridge running approximately parallel to lower edge ( Fig. 13 ). In dorsal view ( Fig. 12 ) slightly expanded from base to middle, then gently narrowing towards apex. Lancet ( Fig. 17 ): 19 annulets; a single, robust, ventrally-placed ctenidial tooth on each annulus; serrulae narrow, and small in comparison to length of annulet, not clearly developed on annulus 1 [numbered from base, excluding the radix]. Lance of similar proportions to lancet, with about 12 proximal dorsal serrulae; annular sutures not visible.

Male. Unknown.

Differential diagnosis. As already indicated in our brief comparative review of morphological character states in Hartigiini , Stenocephus janseni sp. nov. is readily distinguished from other known taxa by an unusual combination of characters: claw without angled basal lobe and inner tooth longer and wider than the outer; mandible outer tooth longer than inner and teeth of about same basal width, inner tooth with simple outline (not conspicuously “shouldered”); maxillary palpomere 4 about 1.5× length of 6; lancet with distinct annuli, simple serrulae, and one ctenidial tooth per annulus.

Body colour pattern alone, if stable, might distinguish female Stenocephus janseni sp. nov. from most other West Palaearctic cephid species. Whereas S. janseni sp. nov. has some of the basal terga and sterna entirely pale, most others have only parts of the terga or sterna banded or flecked with pale. In the Hartigiini , Syrista parreyssii (Spinola, 1843) has a similarly coloured body and legs, but differs in its greater body length (female 15–18 mm), temple much longer than length of eye, and a strongly downcurved valvula 3. Janus compressus (Fabricius, 1793) also has some entirely pale terga, but in the female at least terga 3–7 are entirely pale, and the metatibia is largely black, with the base clear-white.

Characters which separate Stenocephus janseni sp. nov. from the four European Phylloecus species ( Ph. etorofensis (Takeuchi, 1955) , Ph. faunus Newman, 1838 , Ph. niger (M. Harris, 1779) , and Ph. xanthostoma (Eversmann, 1847)) are the absence of any pale markings on the head capsule (in the others, there is at least a small pale spot near the eye on the upper inner orbit), maxillary palpomere 4 about 1.5× as long as 6 (others: about equal in length), and its long and thin antennae. Its two metatibial preapical spurs separate S. janseni sp. nov. from Phylloecus species , which have one, and from Caenocephus , which have none.

Etymology. Named after Dipl.-Biol. Ewald Jansen, for his contributions to the study of European Hymenoptera , particularly the sawfly fauna of Germany.

Host plant. Unknown.

Habitat. Woodland dominated by Pinus sylvestris , with much Betula pendula , and some Robinia pseudoacacia and Quercus robur . Diverse woody plants in understorey, such as Populus tremula , Crataegus sp. , Prunus spinosa , and P. serotina . Field layer dominated by grasses, with patches of Rubus fruticosus agg.

Distribution. Germany: Brandenburg.

Figures

Figs 1–6. Stenocephus janseni sp. nov., holotype, female. 1 – lateral, scale bar 5 mm; 2 – head, dorsal; 3 – head, frontal; 4 – head, lateral; 5 – thorax, dorsal; 6 – pronotum, dorsal.

Figs 7–12. Stenocephus janseni sp. nov., holotype, female. 7 – anterior thorax, lateral; 8 – mesoscutellum, dorsal; 9 – metatibial claw; 10 – metatibial spurs; 11 – abdomen base, lateral; 12 – abdomen apex, dorsal.

Figs 13–17. Stenocephus janseni sp. nov., holotype, female. 13 – valvula 3 and cerci, lateral; 14 – maxillary palp; 15 – left mandible [broken tip of external tooth outlined]; 16 – antenna; 17 – lancet.