The neuroecology of a pollinator's buffet: olfactory preferences and learning in insect pollinators

Plants and their pollinators are excellent examples of mutualistic associations that range in specialization, from obligate to generalized mutualisms, with many pollinators interacting with diverse species of flowers while still maintaining specialized associations. Although floral odors have been implicated in mediating these interactions, identification of the odors-and how the odors are represented in the olfactory system-has been elusive, and the manner in which olfactory learning mediates the generalized plant-insect interactions in the field remains unclear. This review details the composition of floral bouquets that elicit strong attraction in pollinators, demonstrating that for some species of plants the composition of the bouquet plays an important role in exploiting the insect's olfactory system, thereby driving innate attraction, whereas other bouquets can be learned as an associative cue for the nectar reward. By associative learning of nonattractive floral odors with a nectar reward-through octopamine-associated modulation of neurons in the antennal lobe-insects have the ability to exploit alternate floral resources when their preferred flowers are no longer present. Such neural mechanisms, present in specialist and generalist pollinators, provides the means by which pollination associations can range from specialized to generalized while permitting insects to exist within a dynamic floral environment.