Scientists Discover How Bees Activate Natural Medicine Against Parasite Infection During Pollination

In a new paper published today in a special issue of Philosophical Transactions of The Royal Society, Kew scientists and partners report on how bees activate the "medicinal" properties of various nectars to protect themselves from parasite infections.

The team of researchers led by Kew scientist Dr. Hauke Koch, in partnership with Professor Mark Brown at Royal Holloway, University of London, collected nectar and pollen samples from linden and strawberry trees at Kew Gardens in West London to determine how bees process the beneficial compounds found within. The researchers found that two compounds naturally found in the nectars of these species are activated by the bees' digestive processes, the gut microbiome (microorganisms) or a combination of both.

The study's primary aim was to discover how these elements and their anti-parasitic qualities can protect bees from the common gut parasite Crithidia bombi. The experiments yielded promising results for bee conservation efforts at a time when pollinators face the increasing threat of decline from climate change, disease, and habitat loss due to agriculture and land use.

Pollination by animals is one of the world's most important species interactions, as plants offer a nutritious reward to insects, birds, and small mammals in exchange for the transfer of pollen. Not only does this process facilitate the reproduction of many plants, but it also serves to support global food production and ecosystems. Scientists are, therefore, alarmed to see mounting evidence of declines in pollinator abundance and diversity.

Among the threats faced by pollinators today are the dangers posed by parasites. Bee parasites can be introduced and spread through global trade routes, and can spill over from managed honeybee colonies to wild pollinators. Their effects on bees are worsened by other stress factors such as pesticide use affecting microbiome health. The bumblebee gut parasite C. bombi is of special interest to scientists, as the parasite is common and known to threaten the survival and development of bumble colonies.

Dr. Hauke Koch, Research Leader in Pollinator Biological Chemistry at RBG Kew and lead author of the paper, says, "Pollinators have diverse microbiomes in their guts and nest environments. These communities of microorganisms can be important for the health of pollinators, for example by defending them against diseases or producing important nutrients. By better understanding the functional importance and contributions of individual members of the microbiome to different pollinators, we may in the future be able to better support their health.

"For example, managed honeybee and bumblebee colonies can be supported through novel probiotics, or healthy microbiomes in wild pollinators can be maintained through a restriction in pesticides that negatively affect the microbiome and through the promotion of plants with nectar or pollen chemistry that stimulate healthy microbiomes."

The first compound analyzed by the team, unedone, was found in the nectar of strawberry trees (Arbutus unedo) and was extracted from strawberry tree honey. The evergreen, shrubby tree is native to Ireland, Western Europe and the Mediterranean, and commonly planted in parks and gardens in the UK. Its nectar and pollen-rich flowers are known to be an important food for bumblebees in the autumn. Honeybees produce a bitter-tasting honey from it that is sought after around the Mediterranean.