Solitary bees (Osmia bicornis) avoid creating single-component pollen provisions from mass flowering crops in favor of trees’ pollen

Abstract

Bees are exposed to a range of stressors in agricultural environments. One of them is introducing rapeseed monocultures that reduces the diversity of available pollen sources and increases the likeliness of pollen diet homogeneity. Nutritional stress can impair bees’ development and is highly likely to reflect in their phenotype. One of the means to assess the effect of environmental stress on bees is measuring wing asymmetry. We hypothesized that low pollen diversity of provisions collected by polylectic bee Osmia bicornis impairs the development of the bees’ offspring. We checked pollen composition, diversity, percentage of dominant pollen type, content of Brassica napus and Quercus pollen in the provisions. Then we modeled how these pollen traits impact wing size and asymmetry. Palynological analyses both from this study and cross-reference analysis revealed that even when placed in the center of rapeseed field, O. bicornis do not form homogeneous provisions from rapeseed pollen. Adversely, the content of Quercus pollen in pollen provisions is relatively high. The pollen composition of larval provision has an influence on the size of wings, but not on the fluctuation asymmetry in O. bicornis. Our results support earlier reports that wing size reflects response to nutritional stress better than wing asymmetry.