Availability of suitable nectar and pollen resources is a limiting factor for pollinator survival, with both overall resource quantity and quality, along with provision throughout the season, being critical. Yet, our understanding of how the selection of floral resources changes over time, and how this relates to floral availability within the landscape is limited. To fill this knowledge gap, we characterise floral use by honeybee (Apis mellifera) colonies, in a diverse horticultural and agricultural landscape, from April to September, over two years, using pollen DNA metabarcoding of honey samples. We compared the pollen found to the availability of host plants within the surrounding landscape using floral surveys. Honeybees used a total of 143 plant taxa, but only 10 of these were determined as major sources (>10% of total sequence reads in any month) and total plant use represented a small proportion of the available floral resources (23% of genera). Distinct patterns of diet specialisation were identified in June and August, where colonies diverged in their floral preferences before re-aligning in July and September. Following optimal foraging theory, these patterns represent periods of resource limitation. Honeybees showed a preference for flowering trees in the spring, followed by shrubs and herbs in summer and used native and near-native plants more than horticultural plants, as major food sources. DNA metabarcoding allows an increased ecological insight into floral resource use by honeybees and highlights the importance of providing continuous and sufficient floral resources throughout the year.

Anthropogenic activities are leading to changes in the environment at global scales, and understanding these changes requires rapid, high-throughput methods of assessment. Pollen DNA metabarcoding and related methods provide advantages in throughput and efficiency over traditional methods, such as microscopic identification of pollen and visual observation of plant-pollinator interactions. Pollen DNA metabarcoding is currently being applied to assessments of plant-pollinator interactions and their responses to land-use change such as increased agricultural intensity and urbanisation, surveillance of ecosystem change, and monitoring of spatiotemporal distribution of allergenic pollen. In combination with historical specimens, pollen DNA metabarcoding can compare contemporary and past ecosystems. Current technical challenges with pollen DNA metabarcoding include the need to understand the relationship between sequence read and species abundance, develop methods for determining confidence limits for detection and taxonomic classification, increase method standardisation, and improve of gaps in reference databases. Future research expanding the method to intraspecific identification, analysis of DNA in ancient pollen samples, and increased use of museum and herbarium specimens could open further avenues for research. Ongoing developments in sequencing technologies can accelerate progress towards these goals. Global ecological change is happening rapidly, and we anticipate that high-throughput methods such as pollen DNA metabarcoding are critical for assessing these changes and providing timely management recommendations to preserve biodiversity and the evolutionary and ecological processes that support it.