Introduction

Animal-assisted sexual reproduction in flowering plants–pollination – is a phenomenon in which volatile signal production and chemical communication play important and diverse roles. Plant–pollinator interactions are of paramount importance in terrestrial biology, because they bind together food webs within complex ecosystems (Gilbert, 1980), drive co-adaptive evolution among hundreds of thousands of plant and animal species (Feinsinger, 1983; Williams, 1983), and frequently determine agricultural productivity (Metcalf, 1987; Robacker et al., 1988). Most plant–pollinator relationships are considered to be mutually beneficial, such that plants derive reproductive benefits (pollen export and deposition, fertilization) in exchange for resources (nectar, pollen, oils) that directly or indirectly enhance the pollinator's fitness (Heinrich and Raven, 1972; Proctor et al. 1996). In this context, floral scent functions alone or in conjunction with visual cues (e.g., Ômura et al., 1999a) to attract pollinators, induce them to land, indicate a reward's presence and location, and teach pollinators to associate the reward with specific flowers (reviews: Dobson, 1994; Raguso, 2001).

Recent investigations have uncovered a rich panorama of odor-mediated–plant-pollinator interactions, including cheating and exploitation by either party, as well as third-party interventions by predators of the plant or its pollinator (Nishida et al., 1997; Pellmyr, 1997; Gibernau et al., 1998). Therefore, for modern chemical ecologists, the simple question “why do flowers smell?” has given way to more beguiling questions, such as “why do flowers have different odors?”, “why do flowers change their scents?”, and “why don't flowers have stronger odors?”.