11. Bombus (Alpigenobombus) angustus Chiu, 1948

Figs 104‒105

Bombus (Alpigenobombus) angustus Chiu, 1948: 59.

Species-taxon concept and variation

Evidence for the taxon concept of the species B.angustus here provides further support for the interpretation (Williams et al. 2022b) that this is separate from the taxon concept of the species B. breviceps (Williams 1998), 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 PTP and morphological results (Fig. 12, keys) support the interpretation that B. angustus and B. breviceps are separate species (Williams et al. 2022b). The available COI-barcode-like sequences may all be low-divergence neonumts (Fig. 11).

The female mandible of B. angustus has been imaged by Starr (1992: fig. 6a).

No substantial colour-pattern variation of B. angustus is known (Figs 104‒105). Bombus angustus, with its black with red-tailed colour pattern from Taiwan, appears to mimic the commoner local B. (Megabombus) trifasciatus Smith, 1852 (Williams 2007: fig. 5e).

Type material

Bombus (Alpigenobombus) angustus Chiu, 1948: 59. Holotype by original designation: ♁ Taiwan (TARI). Photographic images examined.

Morphological diagnosis

Female

Wings very weakly clouded with brown, nearly clear, with the veins dark brown (cf. B. genalis, B. breviceps, B. grahami), hair of medium length, oculo-malar area shorter than broad, clypeus in its central area with many small punctures (cf. B. genalis, B. grahami); mid and hind tibiae with the exoskeleton and hair predominantly black, hair of the thoracic dorsum and T1‒3 black, T4‒6 orange-red.

Male

Examined from photographic images, also described and genitalia illustrated by Chiu (1948: fig. 1) (genitalia of the type not found by C.-F. Lee, pers. com.): wings very weakly clouded with brown, nearly clear, with the veins light brown; genitalia with the gonostylus nearly equally short on both its outer side and its inner side but with the distal lobe projecting inwards as a long broadly triangular pointed process; hair of the thoracic dorsum and T1‒3 ‘black’ (on the type specimen, which is in poor condition, hair of the thorax in part?faded to brown), T4‒7 orange-red.

Material sequenced in Fig. 12

TAIWAN • 1 ♀ (worker); Chiayi, Alishan; [23.446° N, 120.794° E]; 14 Jul. 2020; Y. Lin leg.; GenBank seq: MZ831894; TFRI: AG#074.

Global distribution

Taiwan endemic (Williams et al. 2022b): PW, TARI, TFRI.

This is a rare species with few individuals recorded: Chiu (1948) lists three individuals from three localities; Starr (1992) lists 21 individuals from eight localities (mapped in Starr: fig. 7) among a total sample of 4555 Taiwanese bumblebees (<0.5%; from his map fig. 7, most B. angustus appear to be from elevations around 1000‒2000 m, although one individual in the north may be from ca 100 m).

Behaviour

Male behaviour not seen.