POLLINATORS STRATEGIES IN FINDING FLOWERS

Two phases of foraging flights of hymenopteran pollinators are discuss ed: localization of food sources over far distances (hundreds of meter s to several kilometers); and spotting of flowers within their visual catchment area. In the first part, evidence from navigational tasks wi th honeybees is presented which favors the interpretation that bees po ssess a rich and unique spatial memory of qualified and localized obje cts. Depending on the motivation, the bee is rather free to navigate w ith reference to this memory. In particular, bees are guided towards f eeding places with specific expectations of their signal and reward pr operties. In the second part, the processes guiding the bee during its final approach to the flower are analyzed. When arriving in the close vicinity of a rewarding flower, bees first detect and recognize the a chromatic green signal and then the chromatic color signal. The depend ence on the optical signals of the flowers and the habitat features is studied in a comparison between plants growing in the Israeli Mediter ranean and desert habitats. We find that the green contrasts of flower s in desert plants are less prominent than in Mediterranean plants bec ause the green signal of the desert background is more similar to that of flowers, not because the green signals of desert and Mediterranean plants are different. These results are interpreted on the assumption that the green signal of flowers used in further distance detection i s an adaptive property of plant species only in the context of all fea tures supporting navigation bf insects. The low density growth of dese rt plants may allow for the possibility that the plants are located by insect pollinators as specified places relative to landmarks. Therefo re, further distance visual signals emanating from the flower may be l ess important in a desert habitat, and reduced green contrast does not become an unfavorable property in desert plants. We conclude that bot h habitat features and flower signals contribute to the navigational s ystem of insect pollinators, and that the evolutionary development of flower signals needs to be evaluated in the context of the plant speci es' habitat.