Plants for pollinators: New DNA research reveals fascinating insights into the plants used by bees and hoverflies

A study into the foraging habits of insects is providing a greater understanding of the world of precious pollinators.

“Here at the Botanic Garden, we have been working hard over the past few years to find out what plants are used by pollinators.” said the study’s lead author Dr Abigail Lowe, Botanical and Invertebrate Researcher at the National Botanic Garden of Wales. “We wanted to provide seasonal recommendations to gardeners to ensure pollinators are appropriately supported throughout the year.”

Abigail examined the pollen found on hundreds of hoverflies, honeybees, bumblebees, and solitary bees collected between March and September over two years. “It was important for us to capture information from a diversity of species”, said Abigail. “Many people are aware of the importance of bees but might not be aware of other insects that need their help”.

The plants visited by individual insects were identified by analysing fragments of DNA contained within the pollen grains on their bodies, a process known as DNA metabarcoding. This information provided a detailed understanding of the preferences of insects, including key differences in foraging between bees and hoverflies.

“It’s really not enough to know whether a plant is good for pollinators. We have to know which pollinators and which plants and how that differs through the year, to be better at providing pollinators with a year-round menu”, said Prof Natasha de Vere, Associate Professor and Curator of Botany at the Natural History Museum of Denmark, who supervised and conceived the study.

Abigail said “We have to ensure that food is available during key times in the life cycles of pollinators. For example, early spring is a crucial time for a queen bumblebee as she emerges from hibernation looking for pollen to start building her nest.”

In this study, bumblebees, honeybees, solitary bees, and hoverflies were often found to visit the same plants, however, key differences were seen between the plants used most abundantly by bees and hoverflies. Dandelion, buttercups, and lesser celandine were the favourites in the spring. In the summer, bramble was popular with both bees and hoverflies but bees particularly like knapweeds, thistles, and cat’s ear whilst hoverflies favour angelica and hogweed. In the autumn, Rudbeckia, Helenium, Bidens and Coreopsis came out on top.

This work highlighted the importance of native plants within pollinator’s diets. However, the news for gardeners and growers is good: keep doing what you’re doing because garden plants are a vital food source, particularly during the later months when native plants have finished flowering. Results showed that 39% of pollen DNA collected from insects in autumn came from horticultural plants, in comparison to 3% in spring and 6% in summer.

The Botanic Garden has already used this research to support growers in providing pollinator-friendly plants which are not only used by pollinators but have no synthetic insecticides and are grown in peat-free compost. The Saving Pollinators Assurance Scheme gives gardeners the confidence to know, with the indication of a label, which plants are both good for pollinators and the environment. The Saving Pollinators Assurance Scheme is funded through the Growing the Future project which has received funding through the Welsh Government Rural Communities – Rural Development Programme 2014-2020, which is funded by the European Agricultural Fund for Rural Development and the Welsh Government.

This work was completed as part of Abigail’s PhD, in partnership with Bangor University. Abigail received funding from the Knowledge Economy Skills Scholarships (KESS 2), which is a pan-Wales higher level skills initiative led by Bangor University on behalf of the HE sector in Wales. It is part funded by the Welsh Government’s European Social Fund (ESF) convergence programme for West Wales and the Valleys.

 

Plants used abundantly or frequently by each pollinator group throughout the season
	Spring	Summer	Autumn
Bumblebees	Buttercups and lesser celandine (Ranunculus/Ficaria spp.)	Thistles, knapweeds, cat’s ear (Cirsium/Centaurea/Hypochaeris spp.) Bramble (Rubus spp.)	Aster spp. Clematis spp. Bramble (Rubus spp.)
Honeybees	Buttercups and lesser celandine (Ranunculus/Ficaria spp.) Dandelion (Taraxacum officinale)	Thistles, knapweeds, cat’s ear (Cirsium/Centaurea/Hypochaeris spp.) Bramble (Rubus spp.)
Solitary bees	Geum Buttercups and lesser celandine (Ranunculus/Ficaria spp.) Dandelion (Taraxacum officinale)	Bidens/Coreopsis spp. Rudbeckia/Helenium spp.
Hoverflies	Buttercups and lesser celandine (Ranunculus/Ficaria spp.)	Angelica and Hogweed (Angelica/Heracleum spp.) Thistles, knapweeds, cat’s ear (Cirsium/Centaurea/Hypochaeris spp.) Bramble (Rubus spp.)	Angelica and Hogweed (Angelica/Heracleum spp.) Bidens/Coreopsis spp. Rudbeckia/Helenium spp.

 

Abigail’s top tips to help pollinators in your garden:

• Provide plants throughout the season by reducing mowing to encourage plants such as dandelion and buttercups in spring and planting late flowering asters such as Rudbeckia/Helenium, Bidens/Coreopsis and Aster for forage in the autumn.
• Reduce scrub management to encourage bramble Rubus fruticosus.
• Eliminate the use of pesticides, herbicides, and peat in your garden
• Provide suitable nesting habitat within gardens e.g., bee hotels for aerial nesters and both short and long grass for ground-nesting bees.
• Provide aquatic habitats and decaying wood to encourage a diversity of hoverflies.