Floral volatiles in a sapromyiophilous plant and their importance in attracting house fly pollinators

Floral scent in sapromyiophilous plants often consists of complex blends with not only fetid (e.g., sulfides) but also sweet (e.g., terpenoids) volatile organic compounds and a recent study suggests that both groups of compounds are involved in pollinator attraction. However, little is known about the number and identity of compounds involved in pollinator attraction in these deceptive plants that mimic breeding sites of fly pollinators. In the present paper, we studied flower volatiles of sapromyiophilous Periploca laevigata and their capability to elicit biological responses in one of the pollinator species, Musca domestica. Floral volatiles were collected by dynamic headspace and analysed by gas chromatography-mass spectrometry (GC-MS), and electrophysiological (GC-EAD) and behavioural assays (two choice olfactometer) were conducted. In the floral scent of P. laevigata, we detected 44 compounds, of which indole, β-caryophyllene, and germacrene D, as well as dimethyl trisulfide, which was present in trace amounts, were electrophysiologically active in the antennae of M. domestica. However, when we evaluated in behavioural experiments the attractiveness of the electrophysiologically active compounds (complete mixture against partial mixtures or against single compounds) we found that indole was the only attractive compound for the flies. Our results highlight that in this plant – pollinator combination the fetid compound indole plays the major role in attracting house fly while sweet scents emitted from P. laevigata look ineffective.