Bombus eurythorax Wang, 1982

Williams, Paul H., Altanchimeg, Dorjsuren, Byvaltsev, Alexandr, Jonghe, Roland De, Jaffar, Saleem, Japoshvili, George, Kahono, Sih, Liang, Huan, Mei, Maurizio, Monfared, Alireza, Nidup, Tshering, Raina, Rifat, Ren, Zongxin, Thanoosing, Chawatat, Zhao, Yanhui & Orr, Michael C., 2020, Widespread polytypic species or complexes of local species? Revising bumblebees of the subgenus Melanobombus world-wide (Hymenoptera, Apidae, Bombus), European Journal of Taxonomy 719, pp. 1-120 : 54-56

Bombus eurythorax Wang, 1982 stat. rev.

Figs 13 , 55–63 , 186

Bombus eurythorax Wang, 1982: 439 .

Bombus pyrosoma (part) – Williams 1991: 101. — Saini et al. 2015: 116, 211 (non Morawitz, 1890: 349). Bombus miniatus (part) – Williams 1998: 133 (non Bingham, 1897: 552).

Bombus avinoviellus – Saini et al. 2015: 240 (non Skorikov, 1914a: 126).

Bombus eurythorax was described originally by Wang (1982) on the basis of supposed slight differences in the colour pattern of the hair from B. flavothoracicus (= B. miniatus s. lat.): in particular it was suggested that the queen B. eurythorax has the ‘thorax with [a] black interalar band, where intermixed with some hoary-yellow fine hairs’ (even though these are often less pronounced than in B. miniatus s. str., see below). Bombus miniatus s. lat. was subsequently treated as a widespread Himalayan species by Williams (1998), to include the taxon B. eurythorax . Here, B. eurythorax is recognised as a west Himalayan species separate from the east Himalayan B. miniatus s. str., because of their unique and strongly divergent species coalescents in the COI gene ( Fig. 10 ), corroborated by dfferences in morphology. The morphological differences are subtle, but do appear to support the two as separate species within a morphologically more distinctive complex of miniatus s. str. + eurythorax .

Our PTP analysis ( Fig. 10 ) supports relatively strongly two coalescents in the COI gene for the west Himalayan B. eurythorax and the east Himalayan B. miniatus s. str. (sequenced here only from Bhutan). The two coalescent groups differ in COI barcode sequences for at least 21 diagnostic nucleotide positions (3.1% of the barcode region, although some sequences are incomplete). These nucleotide differences are all synonymous, making no difference to the amino acid sequences at translation.

From morphology, B. eurythorax usually has a darker colour pattern of the hair than B. miniatus s. str. for the females (larger workers and queens). The pale hair is also less extensively intermixed in the dark band between the wing bases for B. eurythorax (despite the original description of that taxon, see above). All of the larger females (queens and workers) of B. eurythorax have the yellow bands on the thorax and T1 brownish or yellow rather than grey or cream-white as for B. miniatus s. str. There are a few individuals from the Kishanganga Valley in Pakistan that show a paler hue of the pale bands on the thorax and pale hairs intermixed between the wing bases more similar to B. miniatus s. str. Bombus eurythorax queens usually have T2 anteriorly with a distinct patch of yellow hair that is usually lacking in B. miniatus s. str.

Available samples of the candidate species miniatus are small and mostly old, so the status of the two candidate species remains uncertain. Current restrictions on collecting and sequencing in the areas where these two candidate species are most likely to occur in proximity ( Fig. 13 ) make clarifying their status difficult. However, more evidence is needed to increase confidence in any interpretation of the status of the candidate species miniatus s. str. and eurythorax . Speciation between B. eurythorax and B. miniatus s. str. may have arisen through vicariance between populations of the western and eastern Himalaya caused by a period of altered climate (cf. B. prshewalskyi / B. rufofasciatus ).

Females of B. eurythorax show pronounced size-dependent dimorphism in the colour pattern of the hair: large queens have T2 predominantly black and T4 white; whereas the smaller workers have T2 light chocolate brown and T4 red. Males have the thoracic dorsum and T1–2 extensively yellow and T3–5 extensively yellow or orange-red, often with posterior fringes yellow. That these castes and sexes are conspecific has been confirmed from variation examined within one colony excavated in Kashmir ( Williams 1991).

Diagnosis

Females

Queens large body length 21–24 mm, workers 10–16 mm. Can be distinguished by the combination of the thoracic dorsum with some distinctly yellow hair and T5 at least posteriorly white (cf. B. miniatus , B. rufofasciatus , B. friseanus , B. keriensis , B. richardsiellus ).

Males

Body length 15–16 mm. Can be distinguished reliably at present only by their COI sequence, but hair of T3–7 often orange in part with at least posterior yellow fringes (cf. B. miniatus ). Genitalia ( Fig. 186 ) with the gonostylus much reduced, less than a quarter as long on its outer side as broad, with the distal edge concave and the inner distal corner with a single pronounced spine, the inner basal process acutely produced (cf. other rufofasciatus -group species except B. miniatus ); volsella with the inner distal corner produced as a narrow curved hook ( cf. rufipes -group, B. simillimus , lapidarius -group, sichelii -group, keriensis -group); eye unenlarged relative to female eye.

Material examined

Holotype

CHINA • ♀ (queen), holotype of Bombus eurythorax Wang, 1982 by original designation; Xizang, Nyalam ; 13 May 1974; X.-Z. Zhang leg.; IOZ (examined PW).

Material sequenced (6 specimens)

INDIA • 1 ♂; Kashmir , Gulmarg; 34.0546° N, 74.3856° E; 1 Aug. 1985; P. Williams leg.; BOLD seq: 3262F04; PW: ML4 • 1 ♂; Kashmir , Gulmarg; 34.0548° N, 74.3856° E; 1 Aug. 1985; P. Williams leg.; BOLD seq: 3263F04; PW: ML210 • 1 ♀ (worker); Kashmir , Doodpather; 33.8511° N, 74.5636° E ;

4 Jun. 2012; R. Raina leg.; BOLD seq: 1555G05; RR: ML295 • 1 ♂; Himachal Pradesh, Jalori pass; 31.5370° N, 77.3729° E; 11 Sep. 2004; R. Raina leg.; BOLD seq: 6877G10; RR: ML415 .

NEPAL • 1 ♀ (queen); Karnali, Gothichaur ; 29.198° N, 82.31° E; 30 May 2007; M. Hartmann leg.; BOLD seq: 1550B11; NME: ML183 .

CHINA • 1 ♀ (worker); Xizang, Jilong ; 28.4354° N, 85.2570° E; Jul. 17 2018; IBK seq: BB08; IOZ: ML580 .

Global distribution

(West Himalayan mountain species) East Asia: CHINA: Xizang (southern margin only). – Himalaya: PAKISTAN, INDIA: Kashmir, Himachal Pradesh, Uttaranchal; NEPAL. (IOZ, NHMUK, NME, PW, RMNH, SEHU, SMNS.) The species is widely distributed in the western Himalaya and often abundant.

Behaviour

A colony of this species has been described from underground in a coniferous forest at 2500 m a.s.l. in Kashmir ( Williams 1991). Food-plant generalists and male mate-searching behaviour is patrolling ( Williams 1991).

Figures

Figs 12‒13. Maps of sequenced samples. 12. The rufipes-group and festivus-group. 13. The rufofasciatus- group as recognised as species from the UHF-PTP analysis in Fig. 10. Keys to the coloured symbols are shown on the left (in some cases symbols on the map for one species may overlie symbols for another). Maps projected onto a sphere in ArcGIS using World_Shaded_Relief basemap © 2014 ESRI and showing boundaries between countries as recognised by the UN.

Figs 25–63. Simplified diagrams for the colour patterns of the hair on the dorsum for the species from the integrative analysis. The dorsum is divided into regions, each of which shows only the predominant or most apparent colour for that region using a simplified colour palette, with olive indicating a mixture of black and yellow hair, and grey indicating a mixture of black and white hair. The rufipes-group. 25. Queen, China-Taiwan. 26. Queen, China-Guangdong. 27. Worker, China-Sichuan. 28. Worker, Thailand. 29. Queen, Nepal. 30. Male, China-Sichuan. 31. Male, China-Sichuan. 32. Male, Thailand. 33. Male, Nepal. 34. Male, Nepal. 35. Queen, Indonesia-Sumatra. 36. Queen, Indonesia-Java. 37. Male, Indonesia-Java. The festivus-group. 38. Queen, Nepal. 39. Queen, China-Sichuan. 40. Worker, China- Sichuan. 41. Worker, China-Xizang. 42. Worker, China-Yunnan. 43. Male, Nepal. 44. Male, China- Yunnan. 45. Male, China-Yunnan. The rufofasciatus-group. 46. Queen, India-Kashmir. 47. Worker, India-Kashmir. 48. Male, India-Kashmir. 49. Male, India-Kashmir. 50. Queen, India-Arunachal Pradesh. 51. Queen, Bhutan. 52. Worker, Bhutan. 53. Worker, Bhutan. 54. Male, Bhutan. 55. Queen, India-Kashmir. 56. Queen, India-Kashmir. 57. Worker, India-Kashmir. 58. Worker, India-Kashmir. 59. Worker, India- Kashmir. 60. Worker, Pakistan. 61. Male, India-Kashmir. 62. Male, India-Kashmir. 63. Male, Nepal.

Figs 181‒189. Morphology of the male genitalia for species of the subgenus Melanobombus von Dalla Torre, 1880 from the dorsal aspect, anterior at the bottom of the image, posterior at the top. 181. Bombus eximius Smith, 1852, China-Guangxi. 182. B. rufipes Lepeletier, 1835, Indonesia- Java. 183. B. festivus Smith, 1861, Nepal. 184. B. simillimus Smith, 1852, India-Himachal Pradesh. 185. B. miniatus Bingham, 1897, Bhutan. 186. B. eurythorax Wang, 1982 stat. rev., India-Kashmir. 187. B. prshewalskyi Morawitz, 1880 stat. rev., China-Sichuan. 188. B. rufofasciatus Smith, 1852, India- Kashmir. 189. B. richardsiellus (Tkalců, 1968), Burma (left volsella distal part missing). Scale bars = 1 mm.

Fig. 10. October 2019 (Fig. 8) Bayesian PTP analysis of MrBayes tree of unique COI barcodes (UHF- PTP). Symbols as in Fig. 9.