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

Twenty-four plant species native or naturalized in Britain were grown in th e Cambridge University Botanic Garden, UK and evaluated as potential resour ces for nectar-foraging bees, butterflies and hoverflies. In ten plant spec ies a series of measurements were made, at regular intervals from dawn to d usk, of nectar secretion rate and standing crop, and in all species insect visits were monitored throughout daylight hours. The study revealed differe nces between plant species in the composition of the assemblage of insect v isitors, and in the magnitude and temporal distribution of the nectar rewar d. In some cases we found interesting correlations between temperature and secretion rates or patterns of insect visits. Species that received numerou s insect visits in our study are potentially valuable forage plants that mi ght be planted by gardeners to support local :pollinator populations. Deep flowers whose nectar is accessible to long-tongued bumblebees (Bombus horto rum, B. pascuorum) but not to honeybees may provide long-tongued pollinator s with a resource refuge relatively free from honeybee competition. Feature s that make some of those plant species particularly interesting to observe in the garden include robbing by short-tongued bumblebees in Saponaria, ba seworking by honeybees on closed flowers in Malva sylvestris, and apparent displacement of bumblebees by territorial behaviour of the solitary bee Ant hidium manicatum on species of Stachys. (C) 1999 Annals of Botany Company.