The impact of nectar secondary chemicals on reward evaluation by bumblebees

Project Details

Key Questions

How do bitter-tasting compounds in nectar influence bumblebee evaluation of nectar reward? 


The primary function of nectar is as a reward for pollinators.  However, the nectar of many plant species contains secondary chemicals that are bitter-tasting, toxic, or otherwise detrimental to pollinators1,2.  Pollinators must still consume nectar with such compounds in, otherwise this trait would be maladaptive for the plants concerned.  This project will test how nectar secondary chemicals interact with other nectar components to influence evaluation of reward in pollinating bumblebees. This project will take an approach that is a combination of applied and evolutionary approaches to understand the how bees avoid intoxication.  

Aims of the Project

  1. Determine bumblebee rejection thresholds for a wide range of secondary nectar chemicals 

  1. Investigate how nectar sugars may mask bitter- tasting compounds in nectar 

  1. Use relative reward evaluation experiments to determine the cost of foraging on bitter-tasting nectar 

Project Description

1. Using a taste assay3, you will determine the concentration threshold at which different secondary compounds in nectar become repellent to bees.  A wide range of secondary nectar chemicals will be used including nectar alkaloids and common agrochemicals. Several of these chemicals are found concurrently in the same nectar; for selected compounds you will explore if they have a combinatorial effect (or otherwise) on rejection thresholds. 


2. High sugar in nectar could mask the taste of bitter substances, offsetting the reduction in bee-assessed reward valence.  To investigate this effect, you will: a. Investigate how sugar concentration and composition (e.g. sucrose/fructose/glucose) influences rejection thresholds.  b. Conduct two-way choice experiments with free-flying bumblebees4 where the bees are offered artificial flowers containing sucrose solution with varying concentrations of sugars and secondary nectar chemicals.  This will allow for quantification of any influence of these chemicals on reward valence.  


3. Secondary nectar chemicals typically have a distribution of concentrations across flowers within a plant species.  Using free-flight experiments you will explore how the distribution, mean and variance of secondary chemicals in nectar influence reward valence and bumblebee foraging behaviour. 


Wider impact/context 


With over 20,000 species worldwide, bees are arguably the most important pollinators of flowering plants.  Bumblebees are a key group, with tens of thousands of colonies reared annually in the UK for commercial crop pollination.  Investigating the effect of nectar chemistry on bee behaviour has impacts both for agriculture and bee conservation.  From a more theoretical perspective, resolving how floral nectar traits attract pollinators is crucial for understanding plant-pollinator coevolution. 




  1. Adler, L. S. The ecological significance of toxic nectar. Oikos 91, 409–420 (2000). 


  1. Stevenson, P. C., Nicolson, S. W. & Wright, G. A. Plant secondary metabolites in nectar: impacts on pollinators and ecological functions. Funct. Ecol. 31, 65–75 (2017). 


  1. Ma, C., Kessler, S., Simpson, A. & Wright, G. A novel behavioral assay to investigate gustatory responses of individual, freely-moving bumble bees (Bombus terrestris). J. Vis. Exp. 2016, 1–7 (2016). 


  1. Nityananda, V. & Pattrick, J. G. Bumblebee visual search for multiple learned target types. J. Exp. Biol. 216, 4154–4160 (2013). 

Methods to be used

Behavioural experiments with free-flying and caged bumblebees 

Specialised skills required

Experience designing behavioural experiments,  Statistical analysis. 

Please contact Geri Wright on if you are interested in this project