Linear areas of contrasting floral colour, or “nectar guides”, are recognized to enhance pollinator attraction. Few studies, however, have investigated the role of other types of floral marking in pollinator behaviour. In this study, we explore the impact of petal spots and petal rings on bumblebee foraging dynamics. Using model flowers with discrete spot or bullseye ring patterns we investigate the responses of Bombus terrestris foragers towards rewarding and unrewarding flowers. We find that the presence of petal spots and rings reduce the search time of pollinators to locate rewarding model flowers. Only the rewarding petal ring phenotype, however, is readily learned and significantly increases the foraging efficiency of experienced bees over four foraging bouts. Although the rewarding spot phenotype induces random foraging over this time frame, employing differential conditioning with a strong aversive stimulus over ten foraging bouts reveal that bees have the capacity to correctly identify rewarding spot phenotypes with more training. Once a strong association between petal marking and reward is formed, bees continue to respond to marked phenotypes even when unrewarding, suggesting rewardless plants that exhibit petal marking could potentially exploit their pollinators. We conclude that petal marking, whether organised discretely in a spot or in a continuous ring around the centre of a flower, have a significant and complex influence on pollinator foraging dynamics.
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We thank Matthew Dorling for excellent plant care and for maintaining bee colonies, and Rachel Walker, Corneile Minnaar and Willem Augustyn for helpful discussions. This project was supported by a Royal Society Joint International Project Grant to BJG.
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