Observations onPhacelia tanacetifoliaBentham (Hydrophyllaceae) as a food plant for honey bees and bumble bees

Abstract

To assess the value of Phacelia tanacetifolia Bentham as a food plant for bees, observations were made on the phenology of flowering of plots sown on different dates in south-eastern England, and on the phenology, density, diel periodicity and behaviour of bees that foraged on them. The early May-sown plot flowered from early July until late August, the late May-sown plot from mid-July until mid-September, and the late July-sown plot from late September until killed by frosts in December. Peak flower densities exceeded 2 000, 4 000 and 3 000 flowers/m² for the early, mid- and late-sown plots respectively. Both honey bees (Apis mellifera L.) and bumble bees (Bombus spp. and Psithyrus spp.) foraged on the flowers from early July until late October. At peak bee density > 20 bees/m² were present. Eight species of bumble bee were recorded, Bombus terrestris, Bombus lucorum, Bombus pascuorum, Bombus lapidarius, Bombus ruderarius, Bombus hortorum, Bombus pratorum and Psithyrus vestalis. On two days in July and August foraging commenced at 05.00 h to 07.00 h and ceased at 19.00 h to 21.00 h GMT. Bumble bees reached their maximum density earlier and maintained it for longer than honey bees. Most flower visits were for nectar; only 22% of honey bee visits and 3% of bumble bee worker visits were for pollen. Male and queen bumble bees visited for nectar only. P. tanacetifolia has potential for use as a bee food plant for set-aside and conservation areas, thereby contributing to the survival of populations of pollinators.