Stored pollen in honeybee (Apis mellifera) colonies reveals foraging preferences and nutritional gaps in rapeseed and apple agroecosystems of southeast Spain

Aim of study: In managed pollination, the floral preferences of honey bees are frequently overlooked, which may lead to suboptimal pollination outcomes. This study aims to characterize the nutritional profile of pollen collected by Apis mellifera in rapeseed (Brassica napus) and apple (Malus domestica) monocultures in southeast (SE) Spain, and to evaluate how foraging preferences align with colony nutritional requirements. Area of study: Pollen samples were obtained from honeybee colonies in four rapeseed crops in the Spanish province of Albacete (SE Spain), and in four apple orchards in the northwest of Murcia (SE Spain). Material and methods. Pollen samples were identified using light microscopy and metabarcoding. Physicochemical analyses included measurements of six parameters: moisture, lipid content, nitrogen, ash, amino acid profile, and mineral contents. Statistical significance was determined using the four sites per crop as true biological replicates. Research highlights: Wildflowers were the primary pollen source, while crop pollen was moderately (rapeseed) or minimally (apple) collected. Lipid and protein levels were slightly below the recommended thresholds for a complete honey bee diet. Most essential amino acids met requirements, except for methionine and tryptophan. Manganese, copper, and zinc were the deficient minerals. These results suggest that honey bees preferentially forage on wild flora to compensate for nutritional imbalances in monoculture crops. Honeybees foraged preferentially on wildflowers surrounding the crops, likely due to greater floral attractiveness and resource availability. Competition among co-flowering plants may have influenced foraging decisions, with potential implications for managed pollination systems. Conclusion: Honey bees collected nutritionally diverse pollen predominantly from wild flora rather than from crop species. These findings highlight the importance of maintaining floral diversity in agricultural landscapes to support honeybee nutrition and colony health. Supplementary feeding may be advisable to prevent nutritional deficiencies when colonies are placed in monocultures during early spring.