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 appearanc e of flowers may have nonrandom spatial patterns. Flower visitors may learn the location of nectar in association with spatial position of f lowers or floral color. We observed carpenter bees, Xylocopa micans, f oraging at vertical inflorescences of three artificial flowers one of which always contained nectar. In ten treatments, we manipulated the c olor and spatial position of the nectar-bearing flower to learn how th ey detected its location. Bees arrived at all three flowers equally fr equently when neither spatial nor color information was predictably as sociated with the nectar-bearing flower or when all flowers were the s ame color (only spatial information available). Bees arrived almost ex clusively at the nectar-bearing flower if the color of that flower dif fered from the color of the two empty flowers on the same inflorescenc e. Only in the absence of previously learned color-nectar associations did bees arrive at the nectar-bearing flower using spatial informatio n. Across the treatments, the number of flower visits per inflorescenc e was negatively correlated with the proportion of arrivals at the nec tar-bearing flower. We conclude that carpenter bees used a hierarchy o f information to learn the location of the nectar-bearing flower. Colo r was primarily used to find it, but when no information was given by color the bees used spatial information.