8. Bombus natvigi Richards

(Figs. 116‒123, 136, 144)

< Bombus hyperboreus> var. natvigi Richards 1931:9, type-locality citation ‘Vinterhavnen, Greenland’. Holotype male (#5014) by monotypy, ZMO examined FØ, photo of specimen and genitalia examined PW, ‘Vinter / havnen’ (Greenland). Status revised to Bombus natvigi Richards suggested by Williams et al. (2016:2), confirmed here.

Bombus hyperboreus var. vulpinus Friese 1935:4, type-locality citation ‘Kong Oscars Fjord Vegasund’ (Greenland). Syntype females, not seen (identity not in doubt). Synonymisation with Bombus natvigi Richards suggested by Williams et al. (2016:2), confirmed here.

Alpinibombus hyperboreus eskimo Skorikov 1937:57, type-locality citation ‘grönländischen’. Syntype series, not seen (identity not in doubt). Synonymisation with Bombus natvigi Richards suggested by Williams et al. (2016:2), confirmed here.

[< Alpinibombus hyperboreus > mod. natvigoides, mod. henrikseni Skorikov 1937:57, infrasubspecific.]

BOMBUS (ALPINOBOMBUS) HYPERBOREUS < ssp.> CLYDENSIS Yarrow 1955:151, type-locality citation ‘Clyde Inlet, Baffin Island’. Holotype queen (#184) by original designation, NHMUK examined PW, ‘ Clyde Inlet / Baffin Id’ (Nunavut, Canada). Synonymisation with Bombus natvigi Richards suggested by Williams et al. (2016:2), confirmed here.

Taxonomy and variation. Bombus natvigi has long been considered part of B. hyperboreus but has been recognized as separate from evidence of a species coalescent in the COI gene (Williams et al. 2015; Fig. 9). The support from bGMYC analysis for separation of B. kluanensis, B. natvigi, and B. hyperboreus, was not as high as for the other species of Alpinobombus (Williams et al. 2015), but B. kluanensis is easily distinguished by its social behaviour with abundant workers. Bombus natvigi is vicariant with B. hyperboreus across the Bering Strait (Figs. 116, 124).

Variation in the colour pattern has been illustrated and analysed previously (Williams et al. 2014 (under the name B. hyperboreus); Williams et al. 2015). There is little variation in most females (Fig. 118), with occasional individuals having yellow hair intermixed on the upper side of the thorax (Fig. 117). Males show greater variation, with intermixing of yellow hair extensively on the thorax (Figs. 119‒121) and on T5‒6 (Fig. 119), occasionally with orange hair on T6‒7 (Fig. 119).

Material examined. 223 females 134 males, from USA, Canada, and Greenland (Fig. 116: AMNH BP CNC CR EMEC HUM INHS NHMUK PR PCYU PW RBCM ROM UAM UOG YPM ZISP), with 23 specimens barcoded.

Habitat and distribution. Flower-rich arctic/alpine tundra in the New World including Greenland, north to Ellesmere Island and north Greenland, extending southwards into the subarctic region in the alpine zone of the Alaskan and Yukon mountains (but absent from the Aleutian Islands: records in Milliron 1973 and Richards 1973 are revised here to B. polaris). Regional distribution maps (Milliron 1973; Richards 1973; Williams et al. 2014).

Food plants. (Richards 1931; Milliron & Oliver 1966; Milliron 1973; Richards 1973; Williams et al. 2014)

Behaviour. Some authors have reported workers of B. natvigi (from the New World but under the name B. hyperboreus: Milliron 1973), but we have seen no convincing workers of this species during this study (although some workers of B. kluanensis may be very similar in colour pattern, Fig. 110, and in head shape). Milliron and Oliver (1966) and Richards (1973) interpreted this scarcity of workers as evidence that the species is a social parasite in colonies of other bumblebee species. In this respect B. natvigi is almost unique among bumblebees other than the species of the subgenus Psithyrus (the other exceptions are B. hyperboreus, below, and B. inexspectatus (Tkalců), see Müller 2006). The host species of B. natvigi has been identified as B. polaris (Milliron & Oliver 1966; Richards 1973; Pape 1983). Despite this, some females of B. natvigi (under the name B. hyperboreus) occasionally have compressed pollen in their corbiculae (see comments on B. hyperboreus), which appears to be evidence of foraging for a colony (Pape 1983). There is no evidence of protective mimicry of the host ( B. polaris) in cephalic gland secretions and none of the repellent compounds detected from parasitic Psithyrus bumblebees have been identified (Brasero, Martinet, et al. 2017).

Conservation status. This species has not yet been fully assessed for Red List threat status using IUCN criteria (2001). Hatfield et al. (2016b) have listed B. natvigi as ‘Data deficient’.