by Verweij et al.
Pollinating insects, like bees, are essential for pollinating 75% of crops and many wild plants, making them crucial for both agriculture and natural ecosystems. However, as a result of climate change, agriculture and urbanization their populations are declining. Urban green spaces can help support bees by providing rich habitats with diverse flowering plants. Many ornamental plants sold in garden centers are marketed as bee-friendly, but often this is not confirmed by actual research.
A combination of flower traits, such as nectar, pollen, colour, flower shape and the number of flowers, determine how attractive a flower is to bees. For example, bees prefer flowers that produce plenty of high-quality nectar and pollen and with bright colours, such as blue and yellow. However, they will adapt to visits other colours if those flowers offer better rewards. Additionally, UV-patterns can help bees to locate nectar, and plants with many flowers are more appealing because they provide more food in one place. The depth of the tube that holds the nectar, also referred to as the corolla tube, can affect how easily bees access nectar, which in turn impacts how efficient they collect the nectar. Breeding ornamental plants may reduce the attractiveness of flowers to bees as they it affects these flower traits, e.g. these flowers may not produce any nectar or pollen or may have become too big to be accessible to many wild bees. This is because ornamental plants have been selected to appeal more to humans, rather than bees.
This study examined how flower traits influence bee visitation to different cultivars of eight ornamental plant genera. Of the 119 cultivars we studied, most were not very attractive to honeybees or bumblebees, but a few were highly attractive. Bees responded differently to traits like nectar sugar content, corolla tube depth and flower colour, and to different combinations of these flower traits depending on the plant genera. For example, both honeybees and bumblebees preferred flowers with a high nectar sugar content, but only honeybees preferred shorter corolla tubes. Our findings show that ornamental plants can support bees if selected carefully based on flower traits. Plant breeders can use this information to breed plants that are both beautiful to humans and beneficial to pollinators. However, native plants will remain critical for supporting more specialized and diverse wild bee species. By combining ornamental and native plants, we can create urban green spaces that help sustain healthy pollinator communities.
