Potential use of floral nectar sugar characteristics in plant selection for pollinator habitats

The use of urban green spaces, including gardens, in pollinator conservation initiatives, excites significant public interest but advice on effective plants frequently relies on qualitative data. This study considered pollinator responses to specific nectar sugar characteristics to determine if they offer the potential for the selection of candidate plants. Pollinator feeding on 60 plant species at the National Botanic Garden of Wales was related to their nectar characteristics to investigate response consistency at different taxonomic levels. The feeding frequency of Hymenoptera, particularly the social Hymenoptera, was significantly correlated with the volume of nectar offered by flowers, but greater differentiation between plant species occurred when specific nectar sugar characteristics were considered. Feeding was significantly correlated with the volume of the hexose monosaccharides glucose or fructose for the Hymenoptera, particularly the social Hymenoptera (and for the two social genera analysed individually, <i>Apis</i> spp. <i>Bombus</i> spp.), but not for non-social species. Similarly, feeding visits were correlated with the percentage of glucose or fructose in nectar in the Hymenoptera, social Hymenoptera and non-social groups (including three individual genera tested (<i>Apis spp.</i>, primitively eusocial <i>Lasioglossum</i>, and non-social <i>Andrena</i> spp.). Fewer and less consistent outcomes were recorded when the (disaccharide) sucrose content of nectar was investigated. In comparative analyses conducted for other pollinator groups (Diptera and Lepidoptera), feeding was only found to be correlated with glucose content. The social Hymenoptera are a particular focus of gardeners and the use of percentage glucose or fructose in nectar is discussed as a potential component of a screening approach to identify keystone plant species.