Cuticular hydrocarbon profiles of Himalayan bumble bees (Hymenoptera: Bombus Latreille) are species-specific and show local and elevation related variation

Bumble bees are important pollinators in natural environments and agricultural farmlands and are in particular adapted to harsh environments like high mountain habitats. In these environments, animals are exposed to low temperature and face the risk of desiccation. The Eastern Himalayas are one of the recognized biodiversity hotspots worldwide. The area covers subtropical rainforest with warm temperature and high precipitation as well as high mountain ranges with peaks reaching up to 6000 m, shaping a diverse floral and faunal community at the different altitudinal zones. We investigated the cuticular hydrocarbon profiles of four bumble bee species occurring at different elevational ranges in Arunachal Pradesh, the northeast most state in India. At 17 locations along an elevational gradient we collected workers of two species from lower elevations (B. albopleuralis and B. breviceps; [~] 100m - 3000m asl) and two species from higher elevations (B. prshewalskyi and B. mirus; [~] 2800m - 4,500m asl). The CHC profiles of all four species showed a significant degree of variation in the composition of hydrocarbons, indicating species specificity. We also found clear correlation with elevation. The weighted mean chain length of the hydrocarbons significantly differed between the low and high altitudinal species, and the proportion of saturated hydrocarbons in CHC profiles significantly increased with the elevational range of the bumble bee species. Thus, these four species of bumble bees in the eastern Himalayas seem to adapt their CHC composition to elevation by decreasing water permeability of their cuticle, similar to insects living in dry mountains or deserts habitats.