Composition of aphid alarm pheromones

Analysis of single cornicle droplets from six species of aphid showed the presence of volatile components in addition to (E)-β-farnesene. Compounds identified included (Z,E)-α- and (E,E)-α-farnesene forMyzus persicae and α- and β-pinene forMegoura viciae. WithMegoura viciae, (−)-α-pinene was most important for alarm activity. The major component of the alarm pheromone ofPhorodon humuli was (E)-β-farnesene even though farnesenes are present in the summer hostHumulus lupulus