Bumblebees directly perceive variations in the spectral quality of illumination.

Individual bumblebees were tested on a task of walking along a test tunnel to collect sucrose solution in an initial training illumination condition that simulated natural daylight, and in two spectrally different illumination conditions. Compared to the training condition the bees took a significantly longer time to complete the task in conditions that simulated either an ultraviolet negative illumination environment, or an illumination environment that represented blue skylight. In a control condition, bees did not derive this cue from spectral information reflected from the dark background material. This result shows that bees can directly perceive spectral changes in illumination conditions, even in the context of a task that does not require colour processing. This potentially enables the visual system of bees to have prior knowledge about the spectral quality of illumination conditions in which they may forage. The findings are discussed in relation to both theoretical models and empirical evidence of colour constancy, and it is concluded that bees can use multiple mechanisms to solve the dilemma posed by having to find colour targets in the spectrally different illumination conditions that exist for insects visiting flowers.