When Color Vision Is Not Useful: The Floral Choices of Foraging Bumblebees on Color-Polymorphic Artificial Flowers

Yonatan Bilu, Tamar Keasar, Uzi Motro & Avi Shmida

Naive bumblebees were allowed to forage on 30 color-polymorphic artificial flowers, which were identical in morphology and reward schedule, but were marked by either a human-blue, 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 color morphs deviated significantly from the expected random choice (1/3-1/3-1/3) for more than 50% of the bees. Out of these bees, 38%, 32% and 30% formed a preference for human-blue, human-green and human-white, respectively. The frequency of non-random color choice, and the strength of the deviation from random choice, were highest when the different morphs were placed in separate clusters, lower when they were placed in adjacent clusters, and lowest when they were randomly intermingled. Non-random 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. The specific color preferences of individuals could not be related to their early foraging experiences.

November, 1996
Published in: 
Israel Journal of Plant Sciences 45 (1997), 223-233