COLOR CHOICES OF NAIVE BUMBLE BEES AND THEIR IMPLICATIONS FOR COLOR-PERCEPTION

The innate preferences of inexperienced bumble bees, Bombus terrestris , for floral colour stimuli were studied using artificial flowers. The artificial flowers provided a colour pattern and consisted of a star- shaped corolla and of central colour patches similar to the ''nectar g uide'' of natural flowers. The innate choice behaviour was assessed in terms of the number of approach flights from some distance towards th e artificial flowers and the percentage of approach flights terminatin g in antennal contact with the floral guide. The colours of the floral guide, the corolla and the background were varied. It was shown that the innate flower colour preference in bumble bees has two components. 1. The frequency of approaches from a distance is correlated with the colour difference between the corolla and the background against whic h it is presented. If the corolla colour was constant but its backgrou nd colour varied, the relative attractiveness of the corolla increased with its colour difference to the background. The colour difference a ssessment underlying this behaviour on a perceptual basis can be attai ned by means of colour opponent coding, a system well-established in H ymenoptera. 2. The frequency of antennal contacts with the floral guid es relative to that of approach Eights cannot be accounted for by colo ur opponent coding alone. Whether the approach flights are interrupted , or whether they end in an antennal contact with the ''nectar guide'' is strongly dependent on the direction (sign) of the colour differenc e, not only its magnitude. The choice behaviour requires a unique perc eptual dimension, possibly that of colour saturation or that of hue pe rception comparable to components of colour perception in humans.