Sammendrag
We are studying how plant odour information is encoded in the receptor neurones of heliothine moths. By the use of gas chromatography linked to single cell recordings (GC-SCR) and to mass spectrometry (GC-MS), plant volatiles that are detected by receptor neurones have been identified in two species; Heliothis virescens (America) and Helicoverpa armigera (south Europe, Asia, Australia, Africa, eastern Pacific). According to the plant compounds eliciting responses, 15-20 types of receptor neurones have been classified in these species. The receptor neurones respond to compounds within the chemical groups of acyclic, monocyclic and bicyclic monoterpenes, oxygenated monoterpenes, sesquiterpenes, homo-terpenes, aromatic hydrocarbons and oxygenated aliphatic compounds. The specificity and structure–activity relationships of five of these types have been described in other studies (Røstelien et al. 2000, Chem Senses, Røstelien et al. 2000, J Comp Physiol A, Stranden et al. 2002, Chem Senses, Stranden et al. 2003 J Comp Physiol A, submitted, Stranden et al. 2003 Chemoecology, submitted). We here present other receptor neurone types for which the active components have been identified; one type responding with high sensitivity to the chemical analogs (S)-(+)-linalool and dihydrolinalool. A group of receptor neurones appearing together in the recordings, all responded to oxygenated aliphatic compounds. The activity of these neurones was separated on the basis of different spike amplitudes and waveforms. Typically, the neurones showed narrowly tuning, responding to only a few chemically related compounds out of the hundreds of the constituents present in the various host- and non-host plant materials tested. No overlap of the molecular receptive ranges of the receptor neurone types was found. One exception is for linalool, the key compound for one of the neurone types presented here, and also a secondary active compound for another neurone type tuned to geraniol.
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