ENANTIOMERIC COMPOSITION OF MONOTERPENE HYDROCARBONS IN SOME CONIFERSAND RECEPTOR NEURON DISCRIMINATION OF ALPHA-PINENE AND LIMONENE ENANTIOMERS IN THE PINE WEEVIL, HYLOBIUS-ABIETIS

The enantiomeric composition of seven monoterpene hydrocarbons in head space volatiles of spruce sawdust and seedlings (Picea abies), pine se edlings (Pinus sylvestris), and branches of juniper (Juniperus communi s) was determined by gas chromatographic separation on a beta-Cyclodex trin column. For the six monoterpenes, alpha-pinene, camphene, beta-pi nene, sabinene, limonene, and beta-phellandrene, both enantiomers were present, whereas for 3-carene only the (+)-configuration was found. T he amount of each enantiomer varied considerably both in relation to t otal amount of all of them, and for the six pairs also in relation to the opposite enantiomer. One olfactory receptor neuron in the pine wee vil (Hylobius abietis) showed a strong response to alpha-pinene when s timulated with all four headspace materials via a GC equipped with a D B-WAX column. The same neuron was subsequently tested with repeated st imulations via the GC effluent containing the (+)- or (-)-enantiomer. A marked better response to (+)- than to (-)-alpha-pinene was elicited . Another olfactory receptor neuron that responded strongly to limonen e when stimulated with the spruce volatiles was tested for enantiomers of limonene. This neuron responded more strongly to (-)- than to (+)- limonene, when stimulated alternately with each of the limonene enanti omers. Discrimination between enantiomers by plant olfactory receptor neurons suggests that the enantiomeric ratios of volatile compounds ma y be important in host location by the pine weevil.