5. Bombus (Alpigenobombus) sikkimi Friese, 1918 stat. rev.

Figs 4, 54‒60, 110

Bombus sikkimi Friese, 1918: 82. Examined.

Bombus (Alpigenobombus) nobilis ‒ Burger et al. 2009: 460, misidentification. — Williams et al. 2010: 130, misidentification. — Streinzer et al. 2019: table 1, misidentification.

Species-taxon concept and variation

The taxon concept of the species B. sikkimi here agrees with the recent interpretation (Williams 2022a) that it is separate from the taxon concept of the species B. nobilis (see the comments below on B. nobilis), based on: (1) our PTP analysis supports independent species-level coalescents in the COI gene (Fig. 12); corroborated by (2) diagnostic morphological character states (see the keys).

The morphological results (Fig. 12, keys) support the interpretation that the divergent colour patterns of the yellow-banded taxa sikkimi s. str. and individuals from the Himalaya with an unnamed white-banded colour pattern are conspecific. We have been able to obtain COI barcode sequences so far only from the white-banded individuals, not the yellow-banded individuals. The latter will be needed to confirm the conspecific relationship.

Variation in the colour-pattern diagrams of B. sikkimi in Figs 54‒60 is arranged approximately from east to west within the Himalaya. Bombus sikkimi, with the yellow-banded colour pattern in the west (central Himalaya) of its range (Figs 56–57, 59–60), appears to mimic the common B. (Melanobombus) eurythorax Wang, 1982, and similar species (Williams 2007: fig. 5j), whereas the white-and-yellow-banded colour pattern in the east (eastern Himalaya: Figs 54–55, 58) appears to mimic the abundant B. (Ml.) prshewalskyi (Williams 2007: fig. 5p).

Type material

Bombus sikkimi Friese, 1918: 82. Syntype: ♀ (queen) Sikkim, India (ZMHB). Examined.

Morphological diagnosis

Female

Wings nearly clear with veins dark brown, hair long, oculo-malar area longer than broad, oculo-ocellar areas densely and broadly punctured with scattered medium-sized punctures with many small punctures between them, anterio-laterally to the lateral ocellus with large, medium and many small punctures almost coalescing and without flat shining areas in between (cf. B. nobilis, B. validus); hair on the anterior dorsum of the thorax and of the side of the thorax and scutellum and T1 either grey or olive-yellow, on the scutellum the pale hair anteriorly often deeply divided in the middle by a triangle of black, T2 either predominantly yellow or with large anterior lateral patches yellow.

Male

Wings nearly clear with veins dark brown, hair long, oculo-malar area longer than broad; genitalia (Fig. 110) with the gonostylus short and distally near its midline axis nearly consistently weakly convexly rounded, its outer side about a half as long as its inner side with the two inner corners of the distal lobe rounded, the margin between them concave, penis-valve head weakly recurved, the recurved section only slightly longer than broad at the base (cf. B. nobilis, B. validus); hair on the anterior dorsum of the thorax and of the side of the thorax and scutellum and T1 either grey-white or dull olive-yellow, T2 anterio-laterally yellow, on the scutellum in the middle the grey or yellow nearly completely divided by black.

Material sequenced in Fig. 12

INDIA • 1 ♁; Arunachal Pradesh, Donyi La; 28.9819° N, 95.2403° E; 4 Sep. 2017; NCBS seq: BE961; NCBS: AG#205 • 1 ♀ (worker); Arunachal Pradesh, Sango-Camp; 28.9814° N, 95.2482° E; 4 Sep. 2017; NCBS seq: BE963; NCBS: AG#206.

Additional sequences in Fig. 10 and haplotype duplicates

INDIA • 1 ♀ (worker); Arunachal Pradesh, Sela Lake; 27.5050° N, 92.1016° E; 24 Sep. 2015; J. Neumayer leg.; NCBS seq: BE968; NCBS: AG#005 • 1 ♀ (worker); Arunachal Pradesh, Sango-Camp; 28.9744° N, 95.2542° E; 2 Sep. 2017; NCBS seq: BE942; NCBS: AG#204 • 1 ♀ (queen); Arunachal Pradesh, Nagula; 27.6981° N, 91.8486° E; 30 May 2016; NCBS seq: BE967; NCBS: AG#207.

Global distribution

Himalaya: India (Himachal Pradesh, Uttarakhand, Sikkim, Arunachal Pradesh), Nepal: NCBS, NHMUK, PW, ZMHB.

This species is recorded (under the name B. nobilis) at elevations of 2700‒4300 m in the Himalaya, mostly above the tree line and into the subalpine zone (especially rich in Rhododendron L. species) (Williams et al. 2010; Streinzer et al. 2019). MS identified two nests, at 3860 m (near BE963) and one near Sela Pass at 4230 m.

Behaviour

Male eye not obviously enlarged relative to female eye: males are expected to show ‘patrolling’ behaviour in search of mates (Williams 1991).