Foraging choices of bumblebees on equally rewarding artificial flowers of different colors

Laboratory-reared bumblebees were allowed to forage on 30 artificial flowers which were identical in morphology and reward schedule, but were marked by either a human-blue, a human-green, or a human-white landing surface. The probability of nectar rewards in the artificial flowers, and their spatial distribution, were manipulated experimentally. The bees' color choices in the different experimental treatments were compared. The proportions of visits to the three colors deviated significantly from the expected random choice (1/3,1/3,1/3) for more than 50% of the bees. Of these bees, 38%, 32%, and 30% formed a preference for human-blue, human-green, and human-white, respectively. The frequency of nonrandom color choice, and the strength of the deviation from random choice, were highest when the different colors were placed in separate clusters, lower when they were placed in adjacent clusters, and lowest when they were randomly intermingled. Nonrandom color choice was also more pronounced when the bees were rewarded according to a constant schedule, rather than probabilistically. A statistically significant preference for human-blue was found during the bees' first three visits. The bees' tendency for “runs” of consecutive visits to the same flower color can partially account for their non- random color choices. Effects of innate preferences, early learning, generalization, and search-image formation on color choice are discussed.