(E)-β-Farnesene, the major component of the alarm pheromone of many aphids, is prepared in 65% yield by passing commercial nerolidol through an evacuated column of alumina, treated with pyridine, at 200° C. The product is stored without air and applied to aphids as vapor at low speed (ca. 230 mm/sec) in air or nitrogen. The response of eight economically important aphid species was assessed in the laboratory; over 90% ofMyzus persicae responded in a large scale trial.