Bombus (Thoracobombus) weisi Friese, 1903

Williams, Paul H., Sagot, Philippe, Martínez-López, Oscar, Barajas, Ricardo Ayala-, Mérida-Rivas, Jorge A. & Vandame, Rémy, 2024, A new wave of Mesoamerican bumblebees? Revising the weisi-complex to reject numts and pseudospecies (Apidae: Bombus), Zootaxa 5514 (4), pp. 301-318 : 311-312

Bombus (Thoracobombus) weisi Friese, 1903 , sensu lato stat. rev.

Bombus laboriosus Smith, 1861:153 , not of Fabricius 1804:352 (= Emphoropsis laboriosus (Fabricius)) . Holotype queen Mexico NHMUK (images at NHMUK014025497), examined.

Bombus weisi Friese, 1903:253 . Lectotype queen by designation of Milliron (1960:98) Costa Rica ZMHB, images examined.

Bombus ephippiatus [subsp.] montezumae Cockerell, 1908:344 , replacement name for B. laboriosus Smith, 1861 .

BOMBUS MATEONIS [sic] Cockerell, 1949:487. Holotype male Guatemala USNM (images at USNMENT00534366), examined.

[ B.<ombus> weisi (part B) [ Mexico, Chiapas] Brasero et al., 2019:190.]

[ B.<ombus> weisi (part C) [ Mexico, Chiapas] Brasero et al., 2019:190.]

Diagnosis. Female. (cf. B. nigrodorsalis s. str.) Metasomal T 2 in the middle between the large pits (with hair bases) with the surface weakly sculptured, smooth and shining. Short hair between the antennal base and the ocelli black; hair of the thoracic dorsum usually anteriorly black, at most with a minority of yellow hairs intermixed in a weak transverse band; metasomal T3 usually yellow at least medially but black laterally; hind basitarsus posterior long fringe black.

Male. (cf. B. nigrodorsalis s. str.) Gonostylus as long as broad, triangular, with the inwardly projecting inner basal process strongly sclerotised for a length as much as the breadth of the volsella ( Fig. 5 ); volsella distally (posteriorly) remaining broad and nearly parallel-sided throughout its length beyond the gonostylus; penis-valve head distally straight with the tip rounded. Hair of metasomal T3 with at least a distinct small lateral patch of black.

Description. Female. Queen body length 15‒17 mm, worker 10‒12 mm. Head with the oculo-malar area length / breadth ratio 1.3. Thorax with the mid basitarsus distal posterior corner acutely and spinosely pointed. Hair long, uneven, and black; pronotum and anterior scutum either sometimes with yellow intermixed, forming a weak transverse band connected with the yellow hypoepimeral area, or more usually this band reduced or replaced with black; scutellum posteriorly with a weak yellow fringe, which may be much reduced with black; lateral propodeum yellow; legs including bases, femora, and corbicular fringes black.

Male. Body length 11‒13 mm. Hair long, uneven, and black; mandibular ventral fringe with long curved hair brown; vertex and occiput sometimes mixed with yellow; pronotum and anterior scutum either yellow, forming a transverse band connected with the yellow hypoepimeral area, or often replaced with black; mesepisternum, hypoepimeral area and metepisternum with yellow; lateral propodeum yellow; leg bases and femora sometimes partly yellow; metasomal T1‒2 yellow; T3 yellow, but always with patches of black at least at the sides; T6 at least with a posterior orange fringe; T7 entirely orange. Genitalia shown in Fig. 5 .

Material examined. ECOSUR: 1195 specimens. Data and barcodes for specimens from Figs 2‒3 are available from https://www.ecosur.mx/beesofmesoamerica/ and barcodes are available from a Supplementary File.

Distribution. Bombus weisi is distributed from Durango, Mexico (northernmost point 23.723° N) south to San José, Costa Rica (southernmost point 9.369° N), occurring on both sides of the Tehuantepec Isthmus ( Fig. 6 ). Its elevational range is 1025–3177 m asl through a variety of habitats, from pine or mixed forest to cloud forest, including cultivated land in semi-open areas. 95% of B. nigrodorsalis records are from above 2500 m, while B. weisi is more abundant below this elevation. Bombus weisi has been collected all year round, except in May, with 95% of the records in July to December. Bombus weisi and B. nigrodorsalis are broadly sympatric in some regions of Mexico, from San Luis Potosí to Oaxaca ( Fig. 6 ), but B. weisi extends beyond Mexico southwards as far as Costa Rica ( Labougle, 1990).

Figures

FIGURE 2. Support for apparent species’ gene coalescents from unique haplotypes for COI barcode-like sequences including numts (nuclear copies of mitochondrial sequences), obtained from an evolutionary tree estimated with MRBAYES and using maximum likelihood to fit Poisson-Tree-Process (PTP) models. Numbers at each node show the probability that all daughter sequences to the right are parts of a single unique species. Branches change from blue to red at the node with the best fit (maximum local probability) for the change from inter-species to intraspecies branching PTP models (species’ coalescent nodes). Sequence labels include: sequence length in number of bases; taxon name; country in capitals (if not shown then MEXICO) and province; sequence identification code (E# = ECOSUR#). Sequence labels are followed by the percentage of the bases A and T at the third codon position, where low scores (≤97.6%) are likely to indicate numts. Labels for sequences interpreted as likely lower-divergence numts are shown in orange and for likely higher-divergence numts are shown in red (see Fig. 1). The scale bar represents branch length on the tree in substitutions per nucleotide.

FIGURE 3. Support for species’ gene coalescents from unique haplotypes for COI barcode (orthologous) sequences excluding likely numts (orange and red bars and labels in Figs 1‒2), obtained from an evolutionary tree estimated with MRBAYES and using maximum likelihood to fit Poisson-Tree-Process (PTP) models. Numbers at nodes, treebranch colours, sequence labels, and scale bar as in Fig. 2.

FIGURE 6. Map showing the distributions of samples examined for this study of the weisi-complex: (white spots) taxon nigrodorsalis s. str. (=B. nigrodorsalis stat. rev.); (grey spots) taxon montezumae (=B. weisi stat. rev.); and (black spots) taxon weisi s. str. (=B. weisi stat. rev.). Larger symbols with spots in their centres show locations from which specimens were sequenced for each taxon. Spherical projection with international boundaries as recognized by the UN shown as grey lines. Map projected in ArcGIS using the World_Shaded_Relief basemap © 2014 ESRI.

FIGURES 4‒5. Male genitalia of (4) B. nigrodorsalis and (5) B. weisi from the right lateral aspect, with posterior extremities at the top of the images and dorsal parts to the right of the images.