Discrimination of the bumble bee species Bombus occidentalis Greene and B. terricola Kirby by morphometric, colour and RAPD variation.

The taxonomic status of B. terricola Kirby and B. occidentalis Greene has long been questioned. However recent COI gene sequence data suggests that B. occidentalis and B. terricola do represent good biological species. In this paper we test the hypothesis that B. terricola and B. occidentalis are conspecific by using independent morphometric and genetic (RAPD) data. For comparison we also analyzed one consubgeneric species, B. moderatus (now B. crytptarum), and one non-consubgeneric species B. (Pyrobombus) perplexus. Discriminant function analysis of wing morphometric data correctly classified over 85% of the specimens of B. occidentalis and B. terricola. Analysis of molecular variance of the RAPD data showed a significant difference (P < 0.0001) between B. occidentalis and B. terricola. Colour variation from laboratory reared colonies of B. occidentalis suggests that probably two gene locus inheritance is likely but that hybridization as the sole basis for the colour variation seen in the nominate taxon B. occidentalis can be excluded. We conclude that B. terricola and B. occidentalis should be regarded as distinct species which have recently diverged, and that they can be distinguished by wing morphometrics and RAPD genotypes. Where they are sympatric (e.g. in Alberta) colour pattern variation is confined to B. occidentalis.

Genetic and morphometric evidence for the conspecific status of the bumble bees, Bombus melanopygus and Bombus edwardsii.

The taxonomic status of closely related bumble bee species is often unclear. The relationship between the two nominate taxa, Bombus melanopygus Nylander (Hymenoptera: Apidae) and Bombus edwardsii Cresson (Hymenoptera: Apidae), was investigated using genetic (enzyme electrophoretic) and morphometric analyses. The taxa differ in the color of the abdominal terga two and three, being ferruginous in B. melanopygus and black in B. edwardsii. B. edwardsii occurs throughout California, while B. melanopygus extends north through Oregon, to Alaska and Canada. They are sympatric only in southern Oregon and northern California. The taxonomic status of these taxa was questioned when Owen and Plowright (1980) reared colonies from queens collected in the area of sympatry, and discovered that pile coloration was due to a single, biallelic Mendelian gene, with the red (R) allele dominant to the black (r). Here it is shown that all the taxa, whether from California, Oregon, or Alberta, have the same electrophoretic profile and cannot be reliably distinguished by wing morphometrics. This strongly supports the conclusion that B. melanopygus and B. edwardsii are conspecific and should be synonymized under the name B. melanopygus. Hence, there is a gene frequency cline running from north to south, where the red allele is completely replaced by the black allele over a distance of about 600 km.