Garden blogs

Another piece in the pollinator puzzle: New research reveals fascinating insights into the plants used by bees and hoverflies

by

In the last few years, we have seen an immense increase in public support for pollinators with many choosing to buy pollinator-friendly plants for their garden. Even with these good intentions, it’s not always easy trying to find the right plants.

Many recommendation lists are available, but they are usually inconsistent, poorly supported by scientific research and often don’t specify which pollinator group (bees, hoverflies, moths, butterflies, etc.) they are targeting. For us to make sure we are supporting a range of pollinator groups appropriately through the year, we need a deeper understanding of which plants are used across the season, and by which pollinators.

Our new study, published in the Journal of Applied Ecology, helps to answer some of those questions.

Here at the Botanic Garden, we’ve spent the last few years using our DNA barcoding expertise to study honeybee foraging. Through this we have developed an excellent understanding of which plants are used by honeybees throughout the season, not just in the Botanic Garden, but across the UK.

However, in the UK, honeybees are just one species, while we have around another 280 species of bee. This includes bumblebees (24 species) and the hugely diverse solitary bees, with some of the latter potentially nesting in your bee hotels. We wanted to use our DNA barcoding skills to find out more about what plants other bee species visit too. Our previous research on hoverflies in species-rich grasslands has shown them to be important and overlooked pollinators, so we were keen to include this fascinating group.

From March to October, over two years, I walked along transects in the Garden and surrounding Waun Las National Nature Reserve, collecting any bees (bumblebees, honeybees, and solitary bees) and hoverflies that I found. As the pollen found on insects contains plant DNA, we can use this as a source of information of which plants have been visited by individuals. Once I had collected my insects, I needed to wash the pollen from their bodies, extract the plant DNA, amplify the regions of DNA that we use for identification using PCR (a term everyone is now familiar with!), and then send the samples to be sequenced. After this, we compared the DNA sequences returned to our custom reference libraries, made possible through the Barcode Wales and Barcode UK projects, to find out which plants the insects had visited.

Across the 41 species of hoverfly, six species of bumblebee, nine species of solitary bee and one species of honeybee I collected at the Garden, pollen from 191 different plants was found on their bodies throughout the year. Bees and hoverflies did use a lot of the same plants, but when it came to looking at the largest contributors to their diet, there were significant differences.

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 liked knapweeds, thistles, and cat’s ear whilst hoverflies favoured angelica and hogweed. In the autumn, Rudbeckia, Helenium, Bidens and Coreopsis came out on top.

Even with over 5000 plant taxa from around the world to choose from in this landscape, the majority of plants visited by bees and hoverflies were native and near-native. However, horticultural plants still have a role to play during the later months when native plants have finished flowering, extending the season and providing pollinators with a late food source.

Find out more about the most frequently visited plants found in this study here.

This study is the first chapter to be published from my PhD thesis, a four-year KESS-funded project* that I undertook whilst being based at the Botanic Garden, in collaboration with Bangor University.

This work has already been used to inform our Saving Pollinators Assurance Scheme, a unique label scheme that ensures that plants are proven to be good for pollinators, contain no synthetic insecticides and have been grown in peat-free compost. The Saving Pollinators Assurance Scheme, funded through the Growing the Future project**, gives gardeners the confidence to know which plants are both good for pollinators and the environment.

My 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.

 

* 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.

** The Growing the Future project 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.