Abstract
In several highly specialized plant-insect interactions, scent-mediated specificity of pollinator attraction is directed by the emission and detection of volatile organic compounds (VOCs). Although some plants engaged in such interactions emit singular compounds, others emit mixtures of VOCs commonly emitted by plants. We investigated the chemical ecological bases of host plant recognition in the nursery pollination mutualism between the dioecious Ficus carica and its specific pollinator Blastophaga psenes. Using Y-tube olfactometer tests, we show that B. psenes females are attracted by VOCs of receptive figs of both sexes and do not exhibit preference for VOCs of either male or female figs. Electrophysiological tests and chemical analysis revealed that of all the VOCs emitted by receptive figs, only five were found to be active on female antennae. Behavioural tests show that, in contrast to VOCs presented alone, only a blend with a particular proportion of four of these VOCs is as attractive as the odour of receptive figs, and that if there is a very small change in this blend proportion, the pollinator is no longer attracted. This study revealed that in highly specialized mutualistic interactions specificity could be mediated by a particular blend of common compounds emitted by plants.
Highlights
In several highly specialized plant-insect interactions, scent-mediated specificity of pollinator attraction is directed by the emission and detection of volatile organic compounds (VOCs)
Does the pollinator discriminate between odours of male and female receptive figs? In our olfactometer bioassays, females of B. psenes were significantly more attracted by VOCs released by both summer male and female receptive figs, than by the control (Fig. 2)
Among the VOCs emitted by receptive figs, which compounds are active on B. psenes antennae?
Summary
In several highly specialized plant-insect interactions, scent-mediated specificity of pollinator attraction is directed by the emission and detection of volatile organic compounds (VOCs). This study revealed that in highly specialized mutualistic interactions specificity could be mediated by a particular blend of common compounds emitted by plants. While the nature of the chemical signals responsible for the specific attraction of pollinators has been well studied in the case of sexually deceptive Australian and European orchids[9,10,11,12,13,14], there are still major gaps in our understanding of the signals involved in plant-pollinator encounter in most specialized interactions. Chemical analysis of floral VOCs indicates that not all plants involved in nursery pollination mutualisms emit rare compounds[3] This suggests that the specific attraction of the pollinator in these interactions is mediated by common plant-emitted VOCs. In the 800 interactions between Ficus species (Moraceae) and their pollinating fig wasps (Hymenoptera, Chalcidoidea, Agaonidae) pollinators reproduce within the flowers of the inflorescence, i.e. the fig, they pollinate. Except for one species[6], the composition of the chemical signal responsible for the specific attraction of pollinating fig wasps to figs of their host species is still unidentified
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