Hierarchical use of information by nectar-foraging carpenter bees on vertical inflorescences: Floral color and spatial position

In many plant species, the appearance of flowers and the production of nectar change with flower age. In species where flowers are arranged in groups, on inflorescences, the position of nectar and the appearance of flowers may have nonrandom spatial patterns. Flower visitors may learn the location of nectar in association with spatial position of flowers or floral color. We observed carpenter bees, Xylocopa micans, foraging at vertical inflorescences of three artificial flowers one of which always contained nectar. In ten treatments, we manipulated the color and spatial position of the nectar-bearing flower to learn how they detected its location. Bees arrived at all three flowers equally frequently when neither spatial nor color information was predictably associated with the nectar-bearing flower or when all flowers were the same color (only spatial information available). Bees arrived almost exclusively at the nectar-bearing flower if the color of that flower differed from the color of the two empty flowers on the same inflorescence. Only in the absence of previously learned color-nectar associations did bees arrive at the nectar-bearing flower using spatial information. Across the treatments, the number of flower visits per inflorescence was negatively correlated with the proportion of arrivals at the nectar-bearing flower. We conclude that carpenter bees used as hierarchy of information to learn the location of the nectar-bearing flower. Color was primarily used to find it, but when no information was given by color the bees used spatial information.