Bumblebees of the World Blog Series… #9 Bombus gerstaeckeri17/09/2019
Of all the bumblebees described globally, only three species are described as oligolectic (specialists), which means they have a strong preference for a particular food source. Two species: Bombus consobrinus and B. gerstaeckeri are specialists on plants from the genus Aconitum (Ranunculaceae), which includes Monkshoods, and also B. brodmannicus delmasi, one of the two subspecies belonging to the species B. brodmannicus, shows some degree of oligolectism on the genus Cerinthe (Boraginaceae).
Given their morphological similarity and their food specialisation on Aconitum, it has long been thought that B. consobrinus and B. gerstaeckeri should be two sister species or even two subspecies of the same species. However, the publication of the bumblebee evolutionary history demonstrated that these two species are not sisters. Fascinatingly, the evolutionary event of food specialization on Aconitum plants therefore took place twice, independently. The actual sister species of B. consobrinus and B. gerstaeckeri are B. koreanus and B. supremus, respectively, two species with Asian distributions, which do not show the same specialisation.
Specialisation on plants with such deep flowers requires an extremely long proboscis (tongue) as can be seen in the amazing image above.
Whereas B. consobrinus has a completely palearctic distribution from Norway to Japan, B. gerstaeckeri has a West-Palearctic distribution (Fig. 2) and mainly occurs in fragmented populations across mountainous regions. It is found in the Pyrenees, the Alps, the Carpathians and it is also present in the Caucasus. In the Ukrainian Pyrenees and Carpathians, populations are isolated and made up of a small number of individuals. Four observations in the Romanian Carpathians have also been recorded. When populations exist in isolation like this (Fig. 2), we sometimes find they become genetically distinct from each other over time, but in this case separate populations have remained broadly similar. They were however, more distinct than another more common species, the Garden bumblebee (B. hortorum), which is found across the same areas.
In the Alps and the Pyrenees, B. gerstaeckeri mainly visits the following Aconitum species: Anthora (A. anthora), Monkshood (A. napellus) and Wolf’s bane (A. lycoctonum). Several other food plants are occasionally visited by this species, such as Epilobium angustifolium or Delphinium dubium, probably for the nectar. It is not entirely clear why this specialisation has taken place, however it seems as though B. gerstaeckeri is reliant on pollen from Aconitum plants for larval development, which could be down to the nutritional content of the pollen, but there is also the possibility that toxins within the plants affect this species’ pollen foraging choice.
Links to further information:
Cameron SA, Hines HM, Williams PH, 2007. A comprehensive phylogeny of the bumble bees (Bombus). Biological Journal of the Linnean Society 91: 161-188.
Dellicour S., Michez D., Mardulyn P. 2015. Comparative phylogeography of five bumblebees: impact of range fragmentation, range size and diet specialisation. Biological Journal of the Linnean Society 116: 926-939.
Delmas R, 1962. Notes zoogéographiques et systématiques sur les Bombidae. I. – Le Bombus brodmannicus Vogt des Alpes françaises. Annales de l’Abeille 5(3): 175-179.
Delmas R, 1976. Contribution à l’étude de la faune française des Bombidae (Hymenoptera, Apoidea, Bombidae). Annales de la Société Entomologique de France (n.s.) 12: 247-290.
Konovalova I, 2007. The first record of the rare oligolectic bumblebee Bombus gerstaeckeri
Morawitz (Hymenoptera: Apidae: Bombini) from Ukraine. Annales de la Société Entomologique de France (n.s.) 43(4): 441-443.
Løken A, 1961. Bombus consobrinus Dahlbom, an oligolectic bumblebee (Hymenoptera, Apidae). Proceeding of the XIth Int. Congr. Ent. 1960 1: 598-603.
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Pittioni B, 1937. Bestäubung und Nektarraub beim Gelben Eisenhut (Aconitum vulparia Rchb). Aus der Heimat, Stuttgart 50: 209-213.
Ponchau O, Iserbyt S, Verhaeghe JC, Rasmont P, 2006. Is the caste-ratio of the oligolectic bumblebee Bombus gerstaeckeri Morawitz (Hymenoptera: Apidae) biased to queens? Annales de la Société Entomologique de France 42(2): 207-214.
Tkalců B, 1973. Taxonomie von Pyrobombus brodmannicus (VOGT) (Hymenoptera, Apoidea, Bombinae). Acta entomologica Bohemoslovaca 70 (4): 259-268.