Bombus (Megabombus) gerstaeckeri
The distribution of B. gerstaeckeri is restricted to the southern mountains where it is highly patchy: by places, the species may look common, but then, most specimens are from the same locality. Like Bombus consobrinus, Bombus gerstaeckeri forages mainly on Aconitum spp. It seems still more specialized to these foraging plants.
Ponchau et al. (2006) stressed that the species could show a very low number of worker in some stations. They hypothesized that it could even live in a solitary way, while obviously most queens continue to forage themselves during the whole season. These authors also measured population densities of this species that are extremely low.