Sammendrag
Specificity of olfactory receptor neurones plays an important role in food and host preferences of a species, and may have become conserved or changed in the evolution of polyphagy and oligophagy. We have identified a major type of plant odour receptorneurones responding to the sesquiterpene germacrene D in three species of heliothine moths, the polyphagous Heliothis virescens and Helicoverpa armigera and the oligophagous Helicoverpa assulta. The neurones respond with high sensitivity and selectivityto (–)-germacrene D, as demonstrated by screening via gas chromatography with numerous mixtures of plant volatiles. Germacrene D was present in both host and non-host plants, but only in half of the tested species. The specificity of the neuroneswas similar in the three species, as shown by the "secondary" responses to a few other sesquiterpenes. The effect of (–)-germacrene D was about ten times stronger than that of the (+)-enantiomer, which again was about ten times stronger than thatof(–)-a-ylangene. Weaker effects were obtained for (+)-ß-ylangene, (+)-a-copaene, ß-copaene and two unidentified sesquiterpenes. The structure-activity relationship shows that the important properties of (–)-germacrene D in activating theneurones are the ten-membered ring system and the three double bonds acting as electron-rich centres, in addition to the direction of the isopropyl-group responsible for the different effects of the germacrene D enantiomers.
Vis fullstendig beskrivelse
