The composition and timing of flower odour emission by wild <i>Petunia axillaris</i> coincide with the antennal perception and nocturnal activity of the pollinator <i>Manduca sexta</i>

In the genus <i>Petunia</i>, distinct pollination syndromes may have evolved in association with bee-visitation (<i>P. integrifolia</i> spp.) or hawk moth-visitation (<i>P. axillaris</i> spp). We investigated the extent of congruence between floral fragrance and olfactory perception of the hawk moth <i>Manduca</i> sexta. Hawk moth pollinated <i>P. axillaris</i> releases high levels of several compounds compared to the bee-pollinated <i>P. integrifolia</i> that releases benzaldehyde almost exclusively. The three dominating compounds in <i>P. axillaris</i> were benzaldehyde, benzyl alcohol and methyl benzoate. In <i>P. axillaris</i>, benzenoids showed a circadian rhythm with an emission peak at night, which was absent from <i>P. integrifolia</i>. These characters were highly conserved among different <i>P. axillaris</i> subspecies and <i>P. axillaris</i> accessions, with some differences in fragrance composition. Electroantennogram (EAG) recordings using flower-blends of different wild <i>Petunia</i> species on female <i>M. sexta</i> antennae showed that <i>P. axillaris</i> odours elicited stronger responses than <i>P. integrifolia</i> odours. EAG responses were highest to the three dominating compounds in the <i>P. axillaris</i> flower odours. Further, EAG responses to odour-samples collected from <i>P. axillaris</i> flowers confirmed that odours collected at night evoked stronger responses from <i>M. sexta</i> than odours collected during the day. These results show that timing of odour emissions by <i>P. axillaris</i> is in tune with nocturnal hawk moth activity and that flower-volatile composition is adapted to the antennal perception of these pollinators.