FREQUENCY-DEPENDENT SELECTION BY POLLINATORS - MECHANISMS AND CONSEQUENCES WITH REGARD TO BEHAVIOR OF BUMBLEBEES BOMBUS-TERRESTRIS (L) (HYMENOPTERA, APIDAE)

Bombus terrestris, a typical pollinating insect species, was offered a rtificial flowers of two different corolla colours with the same sucro se solution reward in an array. Common colours were significantly pref erred, and the strength of the frequency-dependent response increased as a result of learning. There were also frequency-independent biases towards blue flowers, probably because blue flowers appeared more cons picuous to bumblebees than yellow flowers, and the degree of preferenc e for blue was greater when flowers had low nectar rewards. Flower-to- flower movements by individual bumblebees between flowers were non-ran dom, were biased to movements within the same flower colour, and were also dependent on morph frequency. The mechanisms governing flower sel ection in bumblebees are discussed. Pollinators foraging similarly in a natural situation would induce positive frequency-dependent selectio n, assortative mating, and directional selection on different corolla colour morphs of the plant population being visited, resulting in stab ilizing selection for a single flower colour.