Dichotrachelus alpestris, STIERLIN, 1878

Germann, Christoph, 2011, Review of the Dichotrachelus alpestris STIERLIN, 1878 species group with evidence for a species complex of D. augusti F. SOLARI, 1946, and D. sondereggeri sp. nov. from Switzerland (Coleoptera, Curculionidae), Contributions to Natural History 17, pp. 1-21 : 3-15

Dichotrachelus alpestris species group

Characterization (modified after Osella 1970): small species (3.2–4.9 mm); 3 rd tarsal segment narrow, about as wide as previous segments; pronotum elongate and cylindrical; rostrum slender, straight to slightly bowed; aedeagus with subtruncated apex; distributed from the Western Alps ( France, Vercors) eastwards to the southern Bernina massif ( Switzerland).

Type material examined: D. walteri : 4 specimens (cMB). A ♂ lectotype and 3 paralectotypes were selected and are designated here in agreement with Recommendation 73F of the ICZN (2000). Label data: 1 ♂: PIEM. – 1946 G. Paradiso C. Arietta 15-7 Barajon // walteri [handwritten] // [Red label] Lectotype Dichotrachelus walteri BARAJON, 1947 des. C. Germann 2011 (= syn. nov. D. alpestris Stierlin, 1878 ). 1 ♂, 2 ♀: first label contains the same indications // D. walteri mihi (handwritten) // [Red label] Paralectotype Dichotrachelus walteri BARAJON, 1947 des. C. Germann 2011 (= syn. nov. D. alpestris STIERLIN, 1878 ). Remark: the apex of the aedeagus of the ♂ paralectotype is damaged.

Proposed synonymy

Barajon (1947: 32) described D. walteri based on "...quattro esemplari (2 ♂ e 2 ♀) di una nuova specie..." "...catturato il 15-7-1946 ..." from Colle Arietta (Gran Paradiso massif). However, already Osella (1970) reported in his revision only minute morphological differences with respect to D. alpestris . These differences are summarized: Elytral vestiture consisting only of dark brownish scales; Striae less pronounced, third interval diverging towards the elytral decline, its width more than twice the size at base; Elytra more oval shaped and gracile; Pronotum laterally more strongly rounded; Eyes slightly bigger and protruding; Rostrum longer and less curved; Scape of the antennae regularly enlarged, longer than D. alpestris . An examination of the type series (cMB), and the examination of further material (cVR), and their comparison with 133 specimens of D. alpestris ( Appendix 1) showed that these differences – including furthermore the shape of the aedeagus ( Figs 11–16 , 20 ) – fall into the variability observed in D. alpestris . Therefore I propose the following synonymy: Dichotrachelus alpestris STIERLIN, 1878 = walteri BARAJON, 1947 syn. nov.

Key to the species of the alpestris species group

1 Elytra laterally rounded with maximal width in the middle. Discal area slightly bulged ( Fig. 10 ). Legs shorter and stout. Apex of aedeagus weakly constricted before tip, apical margin pointed ( Figs 11–16 , 20 ) 3.2–4.6 mm. ................................. alpestris STIERLIN, 1878 (= walteri BARAJON, 1947 ) (Type locality: Switzerland, Waadt, Col de Cheville. Distribution: France, Hautes Alpes, Basses Alpes, Vercors; Italy, Valle d'Aosta, Liguria, Lombardia, Piemonte; Switzerland, Bern, Fribourg, Lucerne, Nidwalden, Obwalden, Schwyz, Ticino, Valais, Waadt)

– Elytra elongated and slightly cone shaped from the base on with maximal width in or shortly behind the middle. Discal area flattened ( Figs 4 , 7 ). Legs longer and slender. Apex of aedeagus constricted before tip, apical margin rounded ( Figs 17–19 , 28 ) ........................................................................... 2

2 Apex of aedeagus regularly attenuated and laterally strongly constricted before tip, fore margin strongly rounded ( Figs 18, 19 , 28 ) 4. 0–4.7 mm. ...... ................................................. augusti F. SOLARI, 1946 species complex (Type locality: Italy, Valle d'Aosta, Champoluc. Distribution: France, Haute Savoie (Form III); Italy, Valle d'Aosta (Forms I and II), Piemonte (Form I); Switzerland, Valais (Forms I to III))

– Apex of aedeagus abruptly attenuated and laterally moderately constricted before tip, fore margin weakly rounded ( Fig. 17 ), 3.8–4.9 mm. ................... ............................................................................... sondereggeri sp. nov. (Type locality: Switzerland, Grisons, Valposchiavo, Corn dal Solcun. Distribution: type locality)

Distribution ( Figs 27 , 28 , Appendix 1)

Dichotrachelus alpestris shows the major distribution of the group. The most eastern finds I know are fairly isolated on the top of Monte Generoso in the canton Ticino. D. augusti form I is restricted to Valle d'Aosta, around the Monte Rosa massif, northwards to the Saas Valley. Form II is known from Great St Bernard, including Val Ferret in Switzerland. Form III is presently only known from Col de Balme. D. sondereggeri sp. nov. is exclusively known from Corn dal Solcun in the Valposchiavo.

Bionomy: D. sondereggeri sp. nov. lives in moss cushions (Bryophyta, Musci) of Grimmia cf. sessitana DE NOT., Racomitrium heterostichum (HEDW.) BRID. , and Tortella tortuosa (HEDW.) LIMPR. Four larvae were found at the type locality (Corn dal Solcun), one in the presumably second, and three in the last larval instar ( Fig. 29 ). Very soon, on July 6 th, one larva pupated under room temperature conditions ( Figs 30, 31 ). The imago hatched about one week later ( Fig. 32 ). Two of the paratype specimens were also freshly emerged when collected. I conclude that D. sondereggeri sp. nov. may develop within one season. D. sondereggeri sp. nov. was exclusively found in or near moss cushions within small scree slopes at the very top of Corn dal Solcun ( Figs 33, 34 ) between 2300–2500 m a.s.l. However, the single specimen collected by C. Besuchet at the foot of a rock was found at a somewhat lower altitude (2050– 2100 m a.s.l.), where dwarf shrub heath dominates the vegetation ( Fig. 35 ).

Derivation of species name: The new species Dichotrachelus sondereggeri is named after the renowned expert of various lepidopteran groups, co-founder and co-author of the famous standard work for lepidopterologists "Schmetterlinge und ihre Lebensräume" and author of "Die Erebien der Schweiz ", gifted field entomologist and amiable colleague Peter Sonderegger (Brügg).

Figures

Figs 11–16: Overview of the variability of the tip of the aedeagus of Dichotrachelus alpestris: 11) Waadt, Anzeindaz; 12) Ticino, Monte Gene-Generoso; 13) Valle Aosta, Colle Arietta; 14) Valle Aosta, Champorcher; 15) Piemonte, Colle della Lombarda; 16) Piemonte, Portette Valdieri.

Figs 17–26: Male and female genitalia. 17–20: Tip of aedeagus: 17) Dichotrachelus sondereggeri sp. nov. from Corn dal Solcun; 18, 19) forms II (Val Ferret), and III (Col de Balme) of D. augusti species complex; 20) D. alpestris from Anzeindaz. 21–23: Spiculum ventrale: 21) D. sondereggeri sp. nov. from Corn dal Solcun; 22) D. augusti form II from Val Ferret; 23) D. alpestris from Anzeindaz. 24–26: Spermatheca: 24) D. sondereggeri sp. nov. from Corn dal Solcun; 25) D. augusti form II from Val Ferret; 26) D. alpestris from Anzeindaz.

Figs 8–10: Dorsal and lateral views: 8) Dichotrachelus alpestris from Monte Viso, male; 9) Ditto from Anzeindaz, female; 10) Ditto male.

Figs 2–4: Dorsal and lateral views: 2) Dichotrachelus sondereggeri sp. nov. from Corn dal Solcun, male; 3) Ditto female; 4) Ditto male.

Figs 5–7. Dorsal and lateral views: 5) Dichotrachelus augusti (form II from Val Ferret), male; 6) Ditto female; 7) Ditto male.

Fig. 28: Map providing a detailed view of the sites of the Dichotrachelus augusti species complex. White squares: D. augusti form I; white circles: D. augusti form II; black circle in white square: D. augusti form III. The respective shape of the apex of the aedeagus is pictured (I: Valle Aosta, Col Ran- zola; II: Val Ferret; III: Col de Balme); no data is available from the single record south of the Valle d'Aosta.

Fig. 27: Map showing sites of Dichotrachelus alpestris species group. Black circles: D. alpestris; black square: D. sondereggeri sp. nov.; white squares: D. augusti species complex.

Figs 29–32: Different stages of Dichotrachelus sondereggeri sp. nov.: 29) last instar larva just before pupation; 30) pupa ventral view; 31) pupa dorsal view; 32) freshly hatched imago. Fotos: C. Germann.

Figs 33–34. Biotope of Dichotrachelus sondereggeri sp. nov. on Corn dal Solcun (2480 m a.s.l.): 33) side peak in loose rocks providing a cold and humid microclimate where moss cushions with larvae were found; 34) detailed view of those moss cushions. Fotos: C. Germann.

Fig. 35: View from about 2100 m a. s. l. to Corn dal Solcun. Dichotrachelus sondereggeri sp. nov. was found in a single exemplar collected by C. Besuchet at this lower altitude. Foto: C. Germann.