Flowers, nectar and insect visits: Evaluating British plant species for pollinator-friendly gardens

Abstract

Twenty-four plant species native or naturalized in Britain were grown in the Cambridge University Botanic Garden, UK and evaluated as potential resources for nectar-foraging bees, butterflies and hoverflies. In ten plant species a series of measurements were made, at regular intervals from dawn to dusk, of nectar secretion rate and standing crop, and in all species insect visits were monitored throughout daylight hours. The study revealed differences between plant species in the composition of the assemblage of insect visitors, and in the magnitude and temporal distribution of the nectar reward. In some cases we found interesting correlations between temperature and secretion rates or patterns of insect visits. Species that received numerous insect visits in our study are potentially valuable forage plants that might be planted by gardeners to support local pollinator populations. Deep flowers whose nectar is accessible to long-tongued bumblebees (Bombus hortorum, B. pascuorum) but not to honeybees may provide long-tongued pollinators with a resource refuge relatively free from honeybee competition. Features that make some of those plant species particularly interesting to observe in the garden include robbing by short-tongued bumblebees in Saponaria, baseworking by honeybees on dosed flowers in Malva sylvestris, and apparent displacement of bumblebees by territorial behaviour of the solitary bee Anthidium manicatum on species of Stachys.