The plant sesquiterpene germacrene D specifically activates a major type of antennal receptor neuron of the tobacco budworm moth Heliothis virescens

Plants release hundreds of volatiles that are important in interactions wit h insects or other organisms. However, knowledge is scarce as to which of t he compounds are detected by the organism's olfactory receptor neurons. In the present study, single receptor neurons on the antennae of the tobacco b udworm moth, Heliothis virescens, were screened far their sensitivities to naturally produced plant volatiles by the use of gas chromatography linked to electrophysiological recordings from single cells (GC-SCR). Plant volati les, collected by aeration of host and non-host plants, were tested on each receptor neuron via parallel GC-columns. Thus, simultaneous recordings of the gas chromatogram and the neuron responses to each component were obtain ed. One type of receptor neuron, appearing in 80% of all experiments, respo nded with high sensitivity and selectivity to one particular component, pre sent in host as well as non-host mixtures. The component, identified as a s esquiterpene hydrocarbon by linked gas chromatography-mass spectrometry, wa s isolated from a sesquiterpene fraction of cubebe oil and identified by NM R as germacrene D. The purified compound was then re-tested via gas chromat ography on the same receptor neuron type, verifying the identification. A w eaker response to another sesquiterpene hydrocarbon was also recorded.