Interspecific variation of inflorescence scents and insect visitors in Allium (Amaryllidaceae - Allioideae)

Allium is a large monocotyledonous genus, with many species of high economic importance. Knowledge of the pollination biology and the chemical ecology of pollination in this genus is far from being complete. We studied flower visitors of some Allium species in their native habitat and how these interaction partners communicate by olfactory cues. Floral volatiles of five Mediterranean species were investigated by dynamic headspace and thermal desorption-gas chromatography/mass spectrometry (TD-GC/MS). Floral visitors were observed and captured. The physiological activity of scent components in antennae of flower visitors and congeneric species was tested by gas chromatographic/electroantennographic detections (GC/EAD). In the scent samples of the five species 36 volatile organic compounds (VOCs) were detected. The species-specific scent profiles were dominated either by one or two aromatic compounds, or by a monoterpene. We recorded several insects on the flowers/inflorescences of the different Allium species, mainly bees and flies, with only a few visitor taxa shared among the studied species. In the physiological measurements, specific/congeneric visitors did not only respond to VOCs of the species they visited, but also to VOCs of species on which they were not recorded. Our study shows that inflorescence scent and visitor patterns do not correlate, and that although single visitors detected compounds of various Allium species, there was only a limited overlap in visitor spectrum among the species. Our study also adds several compounds to the list of floral scents being EAD-active in bees and flies.