Plant-pollinator interactions are vital ecological relationships which underpin global biodiversity and provide key ecosystem services. Despite the importance of pollinators, evidence of species decline is increasing. Declines are caused by multiple interacting factors, however, a reduction in floral resources due to anthropogenic changes in land use is thought to be a major driver. For this reason, there is a requirement for increased knowledge of how plant use is structured within plant-pollinator networks. This information can then be used to ensure sufficient floral resources are provided throughout the year and that pollinator populations are appropriately supported. This thesis begins with a review of the literature surrounding the use of DNA metabarcoding for the identification of floral visitation by pollinators, including a detailed description of the methodological approach and guidance for users of this technique. The following three empirical chapters utilise DNA metabarcoding to identify the most frequently used floral resources by bumblebees, honeybees, non-corbiculate bees and hoverflies throughout the year in a diverse horticultural and agricultural landscape, using pollen from the bodies of insects (chapters three and four) and honey (chapter five). Native and near-native plants were found to be used most often throughout the year. However, horticultural plants offer an alternative resource at the end of the flowering season when native floral availability is reduced. Chapter three identified key seasonal differences in resource use between pollinator orders and functional groups (bumblebees, honeybees, non-corbiculate bees and hoverflies), allowing an evidence-based recommendation list of pollinator-friendly plants to be produced. To further explore floral resource use by pollinators, the levels of dietary specialisation and generalisation were investigated at varying hierarchical levels in chapter four. Whilst generalisation was common at the order, group and species level, individuals were found to be highly specialised both in relation to the number of resources used in a foraging trip and in their dietary niche within a species. In chapter five, the seasonal patterns of specialisation of honeybee colonies revealed periods of resource limitation, although floral surveys identified a higher availability of floral resources throughout the year. The phenomenon of resource limitation is likely due to the reliance of honeybees on mass-flowering resources such as woody trees e.g., Prunus spp. and Salix spp., and bramble Rubus spp. as major resources, of which there is a phenological gap in peak flowering between spring and summer. This thesis deploys novel pollen metabarcoding approaches to provide a temporally explicit evidence base that broadens our understanding of resource use by pollinators. Consequently, we are now in a position to provide informed recommendations to gardeners, landowners, and policy makers to determine which plants can be used for supplemental planting in urban and agricultural habitats and to highlight the importance of conserving semi-natural habitats.