Seasonal progression and differences in major floral resource use by bees and hoverflies in a diverse horticultural and agricultural landscape revealed by DNA metabarcoding.
Gardens are important habitats for pollinators, providing floral resources and nesting sites. There are high levels of public support for growing 'pollinator-friendly' plants but while plant recommendation lists are available, they are usually inconsistent, poorly supported by scientific research and target a narrow group of pollinators. In order to supply the most appropriate resources, there is a clear need to understand foraging preferences, for a range of pollinators, across the season within horticultural landscapes. Using an innovative DNA metabarcoding approach, we investigated foraging preferences of four groups of pollinators in a large and diverse, horticultural and agricultural landscape, across the flowering season and over 2 years, significantly improving on the spatial and temporal scale that can be achieved using observational studies. Bumblebees, honeybees, non-corbiculate bees and hoverflies visited 191 plant taxa. Overall floral resources were shared between the different types of pollinators, but significant differences were seen between the plants used most abundantly by bees (Hymenoptera) and hoverflies (Diptera). 4. Floral resource use by pollinators is strongly associated with seasonal changes in flowering plants, with pollinators relying on dominant plants found within each season, with preferences consistent across both years. The plants identified were categorised according to their native status to investigate the value of native and non-native plants. The majority of floral resources used were of native and near-native origin, but the proportion of horticultural and naturalised plants increased during late summer and autumn. Synthesis and applications. Plant recommendation lists for pollinators should distinguish between bees and hoverflies and provide evidence-based floral recommendations throughout the year that include native as well as non-native plants for use in the United Kingdom and Northern Europe. Specific management recommendations include reducing mowing to encourage plants such as dandelion Taraxacum officinale and buttercups Ranunculus spp., and reducing scrub management to encourage bramble Rubus fruticosus.