Bombus hortorum > Kew Science > Projects > Harmful or healthy? Studying how chemicals in nectar and pollen affect bees

Harmful or healthy? Studying how chemicals in nectar and pollen affect bees

Plant nectar and pollen contain a range of chemicals, some of which have antimicrobial properties. Can diseased bees take advantage of these antimicrobial chemicals and self-medicate?

Project details

Project Leader: 
Funded By: 
Peter Sowerby Foundation

Objectives and outputs

Pollinator decline: a crucial ecosystem service under threat

Insect pollination services are valued globally at more than US$200 billion. Approximately 75% of crops require pollination, while as many as 90% of all angiosperms are animal pollinated and are therefore dependent on pollinator foraging. However, there is strong evidence of wild pollinator declines in the UK and around the world, with potentially severe impacts on agricultural productivity and ecosystem function, and ultimately, on human health and welfare. 

Both man-made and natural pressures impact pollinator health, abundance, and diversity. These pressures include loss of habitat, pesticide application, and parasites amongst others.

Understanding these factors is increasingly urgent, given the recent emergence of new parasites and diseases in wild and managed pollinators. Emergent diseases are believed to be behind rapid and dramatic declines in managed honey bees and wild bumblebee populations in North and South America. Recent work in the UK has shown that honey bee diseases are rapidly emerging in wild bumblebee populations, with potentially devastating implications.

Flowers play a central role in regulating pollinator diseases

Plant chemicals serve as a defence mechanism to reduce herbivore damage, but can also be stored and used by herbivores to reduce parasitism or control predators. These plant-produced compounds are also present in nectar and pollen, the food of adult and larval bees, but are relatively poorly studied in terms of their effects on pollinators.

The role of plant compounds in defending against phytopathogens is well documented. Different plant compounds have both antimicrobial effects and can be toxic to invertebrates. Therefore, if consumed in nectar or pollen by pollinators, they could potentially exacerbate disease and transmission in bees by weakening their resilience to other stresses, or ameliorate disease through their antimicrobial activity.

Furthermore, many pollinator diseases are transmitted via flowers, when an infected bee leaves 'transmission stages' behind that can then be picked up by the next visitor to that flower. Antimicrobial substances in flowers may thus have an important role in preventing disease spread between pollinators.

Our research will help us to understand if floral resources serve as ‘typhoid Marys’, pharmacies or poison cabinets, in addition to their essential role as a food-resource for bees – answering key questions for pollinator health.

Kew’s role

This research is being conducted at Kew by Hauke Koch, the Ann Sowerby Fellow in Pollinator Health at Kew, and Phil Stevenson, Senior Research Leader in Chemical Ecology. The living plant collection at Kew with over 30,000 different kinds of plants, as well as decades of experience in plant phytochemical research, offer an ideal research environment to unravel the role of plant chemistry in bee health.


  • Characterising chemical compounds in pollen and nectar of major UK pollinator plants.
  • Testing effects of nectar and pollen compounds on bee diseases.
  • Studying the interaction of plant compounds, the bee microbiome, and bee parasites.
  • Identifying plants and plant compounds that can improve pollinator health in the UK.


  • Background data on the chemical compounds of pollen and nectar in UK plants.
  • Recommendations of plant species that can promote pollinator health in agricultural and urban environments in the UK.

Partners and collaborators


Prof. Mark J.F. Brown, Royal Holloway, University of London

Further information


McArt, S. H., Koch, H., Irwin, R. E. & Adler, L. S. (2014). Arranging the bouquet of disease: floral traits and the transmission of plant and animal pathogens. Ecology Letters 17: 624-636.

Koch, H., Abrol, D. P., Li, J. & Schmid-Hempel, P. (2013). Diversity and evolutionary patterns of bacterial gut associates of corbiculate bees. Molecular Ecology 22: 2028-2044.

Koch, H. & Schmid-Hempel, P. (2012). Gut microbiota instead of host genotype drive the specificity in the interaction of a natural host-parasite system. Ecology Letters 15: 1095-1103.

Arnold, S. E. J., Peralta Idrovo, M. E., Lomas Arias, L. J., Belmain, S. R. & Stevenson, P. C. (2014). Herbivore defence compounds occur in pollen and reduce bumblebee colony fitness. Journal of Chemical Ecology 40(8): 878-881.

Tiedeken, E-J., Egan, P. A., Stevenson, P. C., Wright, G. A., Brown, M. J. F., Power, E. F., Farrell, I., Matthews, S. M. & Stout, J. C. (2015). Nectar chemistry modulates the impact of invasive plant species on native pollinators. Functional Ecology (online) DOI: 10.1111/1365-2435.12588.