Pollen use by the solitary bee Osmia caerulescens in cherry orchard agroecosystems in Spain

Abstract

Osmia caerulescens is a solitary bee species commonly found in the Iberian Peninsula that seems well-adapted to altered anthropogenic habitats. Using the post-emergence residues present in 965 brood cells coming from 453 nests (reed stems) from 36 cherry orchards in western Spain, we identified the collected pollen, and studied the diet of the species. We evaluated whether there are differences in the diet over the nest construction and between the developmental stages reached by the offspring, and we tested whether the offspring's body size is influenced by the pollen diet. The pollen from Fabaceae species predominated in the samples, followed by Jasione (Campanulaceae) and Echium (Boraginaceae). We did not find differences in pollen richness and diversity between inner and outer cells nor among the developmental stages reached. However different proportions of Echium and Jasione pollen in individuals at different developmental stages and a positive relationship between pollen diversity and female body size were detected. The results suggest that the availability of flower resources, together with different morphological and chemical pollen traits, play a key role in diet composition and offspring development. Pollen analysis, which provides knowledge about diet breadth, is a useful tool in the study of species adapted to human-altered habitats.