Beebread pollen composition is affected by seasonality and landscape structure

Abstract

In honey bee diet, pollen is the primary source of proteins and essential nutrients. High pollen diversity and protein content support honey bee health, enhancing resistance to different stressors. Agroecosystem simplification, with few dominant species flowering for a limited period, can lead to a shortage of forage and a reduction in the variety and quantity of food. We therefore investigated how agroecosystem landscape characteristics influence pollen collection patterns. We collected beebread from 25 apiaries, located in Emilia-Romagna (Northeastern Italy), in March and June 2021 and 2022. We evaluated their pollen diversity and protein content and assessed the relationship with landscape heterogeneity and composition in a 1500 m radius around each apiary. A total of 138 pollen taxa were identified, predominantly from the Fabaceae, Rosaceae, and Asteraceae families. Pollen richness was significantly higher in June than in March for both years. Protein content, on the other hand, was higher in 2021 compared to 2022 and, for 2022 only, in June compared to March. Cluster analysis of the 25 sites according to their landscape characteristics revealed three distinct groups: Group 1 (mainly arable land), Group 2 (mixed arable land and forest), and Group 3 (arable land and permanent crops). Group 1 had lower landscape heterogeneity. Pollen composition did not differ significantly among groups, suggesting that honey bees might expand their foraging area (over the 1500 m radius that we consider) in response to landscape homogeneity, as observed in Group 1 areas. On the other hand, pollen diversity was highest in Group 3, likely due to the variety of fruit tree species and spontaneous flora.