Sofia Dartnell blogs about her research which aims to find out the areas where bees are in particular decline
We are currently lacking an indicator species, or a “canary in the coal mine”, to alert us to areas where bees need help.
Sofia Dartnell
Insects are in decline globally, and pollinator loss is of particular concern. It is said that one in three bites of food we eat is thanks to pollination by bees, underlining the importance of these buzzing creatures. In a time of changing landscapes and politics, bees find themselves in trouble. Meadows are being paved into city sidewalks, and plants are being doused in pesticides to promote agricultural yields. But how are we to measure the health of bees within a certain area, or within even a singular meadow?
We are currently lacking an indicator species, or a “canary in the coal mine”, to alert us to areas where bees need help. This would provide a way to measure the suitability of habitats for bees, a way to target areas for conservation work and a natural way to record whether restoration efforts targeted at bee conservation have been successful.
Which bees are best for targeted conservation work?
When it comes to understanding the landscape-scale impacts of land management on pollinators, honeybees have been used as an indicator of general insect health. Honeybees are perhaps the most famous bee species, ever popular for their ability to produce honey. Due to their widespread use in agriculture, honeybees are now found worldwide. They naturally accumulate environmental pollutants – such as pesticides or heavy metals – in the wax, pollen and nectar within the colony. This gives us a great sense of what is going on within the landscape, and the conditions under which pollination is occurring.
However, honeybees are a domesticated species. They are easily kept in boxes and can be shipped worldwide as necessary for our pollination benefit. A single beehive can house tens of thousands of honeybees. This can cause negative impacts on other native bees, for example, through competition for floral resources. This begs the question: are there ways we can use other bees to understand bee habitats and pollinator diversity?
Bumblebees are another group of social bees. They are larger than honeybees and produce a different frequency of buzzing when they visit plants. Interestingly, some plants have evolved to only release pollen when receiving this bumblebee frequency, including important crops like blueberries and tomatoes. Like honeybees, bumblebees live in a social colony. The queen produces workers, who help her forage for nectar and pollen, alongside their role in raising subsequent worker generations. Unlike honeybee colonies, which persist over many years with their longer-lived queens, bumblebee life cycles are annual. At the end of summer, the entire colony dies, and only newly produced queens survive over the winter, hibernating until spring when they start new colonies.
I study cuckoo bumblebees, a unique subgroup of bumblebees that are obligate parasites. These cuckoos cannot efficiently collect pollen, nor can they produce their own workers. For future generations of parasitic bees to be produced, these cuckoos must invade a colony of their host bumblebee species. This is the only way for them to acquire workers who will raise future parasite generations.
This may sound nefarious, and indeed it seems contradictory to focus conservation attention on a group of bees that, in the process of its natural life cycle, kills other bumblebees for its own success. However, these species are thought to balance the pollinator playing field. Cuckoo bumblebees are quite specific in the bumblebee species they parasitise and can only survive in areas with a high density of their hosts.
This makes sense – parasites need their host to survive. In this process, bringing down host population levels may allow for other wild bee species to thrive in the same areas. After all, a diversity of pollinators is critical to maintaining diversity of plants.
Understanding the cuckoo bumblebee life cycle
In my PhD research, I am working to understand and quantify the success of cuckoo bumblebees. In understanding each step of their life cycle, we can more accurately model their populations across the UK.
Variable UK weather has also been causing problems for bumblebees over the past few years. From the heat wave during the summer of 2022 to the spring rains of 2024, we are seeing worrying declines in these important pollinators.
The Bumblebee Conservation Trust reported severely low numbers of bumblebees this year – with some species decreasing as much as 72%. With their fragile annual life cycle, it is likely we will be seeing impacts of this past summer’s low numbers for years to come. Ultimately, I hope to understand whether cuckoo bumblebees can be used as an indicator species for healthy bee habitats, and as a milestone of habitat restoration.
* Sofia Dartnell [2022] is doing a PhD in Zoology.
