Bumble bees of the Susa Valley (Hymenoptera Apidae)

A survey of bumble bees (Bombus Latreille) of the Susa Valley was conducted at 124 locations between 340 and 3,130 m a.s.l. representative of the whole territory, which lies within the Cottian Central Alps, the Northern Cottian Alps, and the South-eastern Graian Alps. Altogether 1,102 specimens were collected and determined (180 queens, 227 males, and 695 workers) belonging to 30 species - two of which are represented by two subspecies - which account for 70% of those known in Italy, demonstrating the particular value of the area examined with regard to environmental quality and biodiversity. Bombus soroeensis (F.), Bombus mesomelas Gerstaecker, Bombus ruderarius (Mueller), Bombus monticola Smith, Bombus pratorum (L.), Bombus lucorum (L.), Bombus terrestris (L.), and Bombus lapidarius (L.) can be considered predominant, each one representing more than 5% of the collected specimens, 12 species are rather common (1-5% of specimens) and the remaining nine rare (less than 1%). A list of collected specimens with collection localities and dates is provided. To illustrate more clearly the altitudinal distribution of the different species, the capture locations were grouped by altitude. 83.5% of the samples is also provided with data on the plant on which they were collected, comprising a total of 52 plant genera within 20 plant families. The eight predominant Bombus species point out remarkable differences in botanical choices, in fact only three genera (Epilobium, Onobrychis, and Trifolium) were visited by all eight species, and showed very different frequencies between the species.