The effect of sugar solution type, sugar concentration and viscosity on the imbibition and energy intake rate of bumblebees

- We measured bumblebee nectar imbibition rate in a laboratory setting.
- Our artificial nectars varied in sugar concentration (C) and sugar composition (O).
- Bumblebee imbibition rate (I) increases linearly with C up to 27%.
- Over 27%, I starts to decrease, and is influenced by C, viscosity (η) and O.
- Energy intake rate (E) is maximized at 42-56%, and is influenced by C, η and O.

Nectar is an essential resource for bumblebees and many other flower-visiting insects. The main constituents of nectar are sugars, which vary in both composition and concentration between plant species. We assessed the influence of sugar concentration, sugar solution viscosity and sugar solution composition on the imbibition and energy intake rate of bumblebees, Bombus impatiens Cresson (Hymenoptera: Apidae). To do this, we measured their rate of solution intake for 49 different sugar solution treatments, which varied in both sugar composition and concentration. In general, the imbibition rates of bumblebees were found to increase with increasing sugar concentration, probably due to their preference for high sugar concentrations, up to a concentration of 27% (w/w), at which point solutions reached a threshold viscosity of approximately 1.5-1.6 mPa.s. Above this threshold, the increasing viscosity of the solutions physically inhibited the imbibition rates of bees, and imbibition rate began to decrease as the concentration increased. Nevertheless, bumblebee energy intake rate increased with increasing concentration up to about 42-56%. Although we found that sugar solution composition had an impact on both imbibition and energy intake rate, its effect was not as straightforward as that of sugar concentration and viscosity.