How seasonality, semi-natural habitat cover and compositional landscape heterogeneity affect pollen collection and development of Apis mellifera colonies in Mediterranean agro-sylvo-pastoral systems

Context: The reduction in the abundance and diversity of flowering plant species, mainly due to landscape alteration and consequent habitat loss, negatively affects honey bee populations and is the main driver of their decline. To safeguard pollination service and food security, we need to know how landscape characteristics affect the availability of pollen sources and consequently colony performance across seasons. Objectives: We therefore here explore how seasonality, percentage of semi-natural habitat cover and compositional landscape heterogeneity affect the abundance, richness, diversity and composition of pollen collected by honey bees and the development of their colonies in a Mediterranean area where agro-sylvo-pastoral systems are widely spread. Methods: For the purpose of our study, pollen samples were collected over a year from colonies of Apis mellifera placed in four sampling sites selected across a gradient of landscape heterogeneity and where semi-natural habitats were predominant at various levels within an agro-sylvo-pastoral zone. Simultaneously, the extension of the sealed brood of the same colonies was periodically evaluated. Results: We found that the amount of pollen collected by honey bees was positively correlated with the percentage of semi-natural habitat cover and that increasing habitat diversity at the landscape level had a significant positive effect on the richness and diversity of pollen collected by honey bees. In addition, season significantly affected the amount, diversity and composition of pollen collected by honey bees. Furthermore, bee colony growth was positively correlated with richness, diversity and amount of pollen collected by honey bees. Conclusion: Our study highlights the importance of an abundant and diverse pollen diet for honey bee colony development, which in agro-sylvo-pastoral systems seems to be ensured by a heterogeneous landscape dominated by different types of semi-natural habitats.