Legitimate visitors and nectar robbers on Trifolium pratense showed contrasting flower fidelity versus co-flowering plant species: could motor learning be a major determinant of flower constancy by bumble bees?

Abstract

Flower visitors often fly among plants of the same species more often than is expected from plant frequency and distribution, a behavior known as flower constancy. Because of its implications for the evolution of floral traits, whether flower constancy is associated with perceptual stimuli, reward value, and/or flower handling skills has been debated by many authors. However, it remains unknown whether flower handling skill has a substantial influence on flower constancy because flowers that require different handling skills generally also differ in their appearance (i.e., shape). We investigated the foraging type constancy of Bombus terrestris workers that foraged flower patches consisting of two (Trifolium pratense and Trifolium repens) or three (T. pratense, T. repens, and Lotus corniculatus) plant species. In these flower patches, individual bees foraged T. pratense flowers by either one of the two foraging modes that require different foraging techniques (legitimate foraging versus nectar robbing). Behavioral and pollen load analysis indicated that bees sometimes switched their foraging types between legitimate visits to T. pratense and visits to T. repens and between nectar robbing on T. pratense and visits to L. corniculatus, though they rarely switched between other combinations of foraging types. These results indicate that factors other than perceptual stimuli and spatial distribution of plants affected foraging type constancy. After considering other factors, such as the rewards and the sizes of individual foragers, we argue that handling skills required to forage flowers affected flower constancy observed in this study.