GC-MS analysis of volatiles released from wheat infested with a high d
ensity of aphids showed the presence of 6-methyl-5-hepten-2-ol (sulcat
ol). The proportion of enantiomers present in the volatiles was determ
ined by esterifying the mixture with (1S)-(-)-camphanic chloride and q
uantifying the esters. The mixture consisted of 75% (R)-(-) and 25% (S
)-(+). The mixture of enantiomers as well as the racemate showed signi
ficant repellency towards apterous Rhopalosiphum padi in an olfactomet
er (15.7% and 14.4%, respectively, with 10 ng of stimulus). Single ena
ntiomers or a mixture containing 25% (R)-(-)- and 75% (S)-(+)-enantiom
ers were inactive. The results are discussed in relation to the achiev
ement of specificity by aphids in different pheromone-mediated behavio
rs.