Abstract
Flower-visiting insects provide valuable pollination services to wild and cultivated plants necessary for human health and well-being. Insect populations, including honey bees (Apis mellifera L.) and other insects that visit flowers, are in decline. Past studies of plant-pollinator interactions in living collections like botanical gardens and arboreta have concentrated on herbaceous plant species. Pollinator associations of woody plants are relatively poorly understood, despite their large flower production and major contributions to ecosystem services. To investigate plant-pollinator interactions, a survey was carried out at the Arnold Arboretum of Harvard University, a large botanical garden in Boston, Massachusetts. We conducted observations on A. mellifera and other flower visiting insects and the plants they visited, recording insect foraging behavior and gathering environmental data.
Over two field seasons, 19,807 flower visiting insects were observed. 353 unique plant species received honey bee visitation, with honey bees demonstrating clear preferences among woody plants for a number of genera, including Hydrangea, Ilex, Lonicera, Sorbaria, Clethra, Tilia, Tetratium, and Koelruteria. Some herbaceous taxa remained popular among honey bees, including Clinopodium, Helianthus, Allium, and Pycnanthemum. Our results suggest that both plant phylogeny, the evolutionary relationships between plant species, and day of the year have a moderate effect on honey bee visitation of plants, with a Pagel’s λ value of 0.36 (p<0.001) and honey bee visitation increasing each month of the study across both years. Honey bees demonstrated no preference between collecting nectar and collecting pollen overall. We suggest that urban gardens maintain and proliferate their collections of popular flowering woody plants to assist in providing habitat and floral resources to flower visitors.