Pollination floral odors

In sum, both rigorous analyses of floral odors and olfactory/behavioral assays will be required to tease apart the critical factors that underlie pollinator-flower interactions. Recent work from independent sources indicates progress in this area. For example, studies using GC-EAD and conditioned proboscis extension (Wadhams et al., 1994 Blight et al., 1997 Pham-Delegue et al., 1997) have... 

Chapters in this volume consider how plants use chemicals to defend themselves from insect herbivores the complexity of floral odors that mediate insect pollination tritrophic interactions of plants, herbivores, and parasitoids, and the chemical cues that parasitoids use to find their herbivore hosts the semiochemically mediated behaviors of mites pheromone communication in spiders and cockroaches the ecological dependence of tiger moths on the chemistry of their host plants and the selective forces that shape the pheromone communication channel of moths. 

Floral scents are often complex blends of several compounds. These are mainly fatty-acid derivatives, benzenoids, phenylpropanoids, isoprenoids, nitrogen-and sulfur-containing compounds. Knudsen et al. s (1993) comprehensive review of floral odors reported floral scents with as few as three compounds and as many as several hundred. A study of moth-pollinated flowers from the Nyctaginaceae reported as many as 77 compounds in floral scent and as few as one. Studies that have focussed on identifying the site of volatile production in flowers report that they are produced mostly in the petals. Volatiles are both synthesized and released by the epidermal cells or by special glandular trichomes on the petal surface. Other studies have shown that the odor of pollen is also part of the odor signal. ... 

Flower scent is extremely variable between plant species, but often monoterpenes are the dominating group of compounds in floral odor bouquet. Flowers of one plant species can emit more than 100 scent compounds. Linalool, (3-ocimene and p-myrcene are monoterpenes that have been most-oft reported from flowers. Proportion of monoterpenes of the total scent is variable depending on the age of flowers and the part of the flower analyzed, but their proportion in many cases exceeds 50% of the total flower emission. The ratio of different compounds in flower scent affects the composition of pollinating insect communities. Wasps, flies, beetles and butterflies have a different odor preference in addition to preferences of visible flower colors. Specialized pollinator species use the combination of visual and olfactometric cues of flowers to detect their specific host species. 

Tollsten, L., and Bergstrom, J. (1989) Variation and post-pollination changes in floral odors released by Platanthera bifolia (Orchidaceae). Nord. J. Bot. 9, 359-362... 

Not all floral scents consist of fragrant volatiles. Unpleasant odors associated with dung, carrion, urine, rotting fungi, and decaying cabbage and onion have been found in abiotic mimicry in many plant families such as Araceae, Aristolochiaceae, Orchidaceae, and Apocynaceae.103 Several saprophagous insects are attracted to these flowers and act as selective pollinators. 

Males of neotropical euglossine bees (Apidae), called orchid bees, collect odoriferous substances from flowers of orchids and other plants. The floral scents of these species display relatively simple chemical compositions dominated by one or two major components, mostly terpenoids and aromatic compounds such as cr-pinene, 1,8-cineol, eugenol, -dimethoxybenzene (35), 2,3-epoxygeranyl acetate (36), nerolidol, 4-methoxycinnamaldehyde (37), and benzyl benzoate.113 Since the orchid bees have odor preferences, their collection of fragrances leads to specialized pollination of particular plant species. Male bees absorb the floral volatiles with their tarsal hairs, form species-specific bouquets, and finally accumulate them in their hind tibial pouches. These bouquets have potential roles in courtship displays and marking territories.114 115... 

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