City bees' favourite flowers, according to our DNA tracking experiment

February 20, 2019 by Elizabeth Franklin And Caitlin Potter, The Conversation
A buff tailed bumble bee emerges from a crocus covered in pollen. Credit: thatmacroguy/Shutterstock

As cities get bigger and cover more land, the need to make space for wildlife – including insects – in urban areas has become more pressing. Research has shown that cites may not be such a bad place for pollinating insects such as bumble bees, solitary bees and hoverflies. In fact, one UK study of ten cities and two large towns found a greater variety of species in urban areas than in rural areas, while another study showed some UK urban areas hosted stronger bumble bee colonies than those in rural areas.

But other research has found that cities only support the most common pollinators, such as the buff-tailed bumble bee (which is a flexible, generalist forager), and that many species decline in number as urbanisation increases.

One way to help pollinators in is to provide for them to feed on, in an environment which is otherwise empty of flowering plant life. Flowers have been planted on roadsides around the UK for this very purpose.

Planting more flowers is a great idea – but it is difficult to predict which flowers different insects will use the most, and whether enough flowers are being provided for them. This is why, for our recent study, we teamed up with the National Botanic Garden of Wales to find out what some different bee species think of the wildflower strips planted by Bournemouth Borough Council.

DNA paths

Gardeners and councils who want to plant the right flowers to attract bees usually choose them based on how easy they are to plant, and by watching which ones the insects already visit. Instead of doing this, we collected the from bees who were visiting flower patches. Bees were caught and temporally held in a tube before release. The pollen that had fallen or rubbed off of the bee was used for DNA analysis to find out which flowers they had visited.

Roadside flowers in Bournemouth, UK. Credit: Elizabeth Franklin, Author provided

The technique we used is called DNA meta-barcoding. This allows us to look at a specific part of the plant genome and compare it to a database containing DNA barcodes for numerous British plants, created by the National Botanic Garden of Wales. This technique is relatively new and has previously been used to identify pollen in honey and pollen from the bodies of hoverflies to see which plants they had visited.

By collecting the pollen from the bee's body, we can find out the bee's foraging history and get samples from places where you cannot follow the bee – like up in the trees or into people's gardens. And because it is not destructive, there is the potential to collect from an individual more than once.

But why use DNA techniques rather than simply looking at the pollen under a microscope? Well, it takes a long time to process and identify pollen grains with a microscope and DNA meta-barcoding can be done in a few days. In addition, accurately identifying pollen is very difficult even for those with a high level of expertise. The identification results from DNA meta-barcoding are also now comparable to or better than traditional pollen identification under a microscope. There are some limitations, however. In particular, DNA meta-barcoding cannot provide a count of each pollen type in a sample, only a relative proportion.

How DNA meta-barcoding works. Credit: Elizabeth Franklin, Author provided

Our results show that the bees are indeed using the floral patches put out for them in cities – but these areas alone are not enough. Some of the bees' favourite flowers in the Bournemouth sample area were purple tansy (Phacelia), chrysanthemums (chrysanthemum), poppies (Papava), cornflowers (Centaurea) and viper's bugloss (Echium). We also commonly found that they visit garden plants, for example lupins (Lupinus), hydrangeas (Hydrangea), buddleja (Buddleja) and privet (Ligustrum), and wild like brambles (Rubus), sow thistles (Sonchus) and wild lettuce (Lactuca). This shows that bees travel around the urban environment to find what they need, and don't just rely on the small floral strips planted for them. After all, bees need high quality food and variety in their diet to stay healthy, just as humans do.

Our results also showed that different bees like different things depending on their size. For example, small are restricted to using more open flowers like daisies, while bumble bees are less restricted because they have long tongues that can reach into deep flowers. So planters need to cater for all tastes if we hope to support bee diversity.

A bumblebee uses one of Bournemouth Borough Council’s pollinator plantings. Credit: Elizabeth Franklin, Author provided

This study only covered a tiny percentage of the UK's pollinator diversity and there are many other insects such as hoverflies, beetles and butterflies who rely on urban flowers, too. So while the research improves our knowledge on a small number bee species' flower preferences, there is still lots of work to do in order to make cities friendly for a wide range of pollinators.

Explore further: DNA traces on wild flowers reveal insect visitors

Related Stories

DNA traces on wild flowers reveal insect visitors

February 8, 2019

Researchers from Aarhus University, Denmark, have discovered that insects leave tiny DNA traces on the flowers they visit. This newly developed eDNA method holds a vast potential for documenting unknown insect-plant interactions, ...

Sick bees eat healthier

February 7, 2018

Dr Lori Lach, Senior Lecturer at JCU, said the study compared the feeding habits of healthy bees to those infected with the gut parasite Nosema ceranae.

How urban heat affects bee populations

February 22, 2018

North Carolina is home to 500 species of wild bees, yet only a subset of these are common in cities and suburbs. People encourage wild bees by planting flowers and creating pollinator gardens to provide the pollen and nectar ...

Exposure of hummingbirds and bumble bees to pesticides

July 5, 2018

New research reveals that hummingbirds and bumble bees are being exposed to neonicotinoid and other pesticides through routes that are widespread and complex. The findings are published in Environmental Toxicology & Chemistry.

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

EPA adviser is promoting harmful ideas, scientists say

March 22, 2019

The Trump administration's reliance on industry-funded environmental specialists is again coming under fire, this time by researchers who say that Louis Anthony "Tony" Cox Jr., who leads a key Environmental Protection Agency ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.