Facultative use of the repellent scent mark in foraging bumblebees: complex versus simple flowers

Bumblebees leave scent marks on flowers, and use these marks to avoid recently depleted resources. We tested whether the response to such scent marks is fixed, or whether bees can adjust their responses flexibly, depending on floral complexity. Complex flowers require longer handling times and, when foraging on these flowers, bees show spatial foraging patterns that make revisits more likely. Therefore, we examined whether bees responded to scent marks more strongly if they were found on complex flowers, in order to reduce these revisits. To do this, we used two types of artificial flowers that differed in handling time. Bees preferred foraging on short flowers, but accepted both types. However, when they approached flowers, bees were more than twice as likely to reject scent-marked long flowers than short ones, and the effect of scent marks lingered for 60% longer in long flowers. Bees most often rejected long flowers in flight, without direct access to tactile cues indicating floral handling time. Therefore, they solved the task by using the current visual input to recall a memory of floral handling time, and they combined this information with a current olfactory cue, that is, the scent mark.