Variability in Sexual Pheromones Questions their Role in Bumblebee Pre-Mating Recognition System.

Sex-specific chemical secretions have been widely used as diagnostic characters in chemotaxonomy. The taxonomically confused group of bumblebees has reaped the benefit of this approach through the analyses of cephalic labial gland secretions (CLGS). Most of currently available CLGS descriptions concern species from the West-Palearctic region but few from the New World. Here, the CLGS of four East-Palearctic species Bombus deuteronymus, B. filchnerae, B. humilis, and B. exil (subgenus Thoracobombus) are analysed. Our results show high levels of variability in the major compounds in B. exil. In contrast, we describe a low differentiation in CLGS compounds between B. filchnerae and its phylogenetically closely related taxon B. muscorum. Moreover, the chemical profiles of B. filchnerae and B. muscorum are characterized by low concentrations of the C16 component, which is found in higher concentrations in the other Thoracobombus species. This raises the possibility that courtship behavior as well as environmental constraints could affect the role of the bumblebee males' CLGS.

Interspecific Variation in Bumblebee Performance on Pollen Diet: New Insights for Mitigation Strategies.

Bumblebees (i.e. Bombus genus) are major pollinators of flowering wild plants and crops. Although many species are currently in decline, a number of them remain stable or are even expanding. One factor potentially driving changes in bumblebee distribution is the suitability of plant communities. Actually, bees probably have specific nutritional requirements that could shape their floral choices and constraint them in the current context of global change. However, most studies primarily focus on one bumblebee species at a time, making comparative studies scarce. Herein we performed comparative bioassays on three bumblebee species (i.e. Bombus hypnorum, B. pratorum and B. terrestris) fed on three different pollen diets with distinct nutritive content (Cistus, Erica and Salix pollen diets). Micro-colony performance was compared through different developmental and resource collection parameters for understanding the impact of change in pollen diet on different bumblebee species. The evidence suggests that B. terrestris is by far the most competitive species because of its performance compared to the other species, regardless of pollen diet. Our results also highlight a Bombus species effect as pollen diet impacts the micro-colonies in different ways according to the actual bumblebee species. Such interspecific variation in Bombus performance in response to a dietetic change underlines the importance of considering different bumblebee species in mitigation strategies. Such comparative studies are good advice for developing appropriate suites of plant species that can benefit threatened species while supporting stable or expanding ones.