Aphids respond to predator attack by secreting cornicle droplets containing alarm pheromones. (E)-B-farnesene has been identified as the principal alarm pheromone from aphids in 18 genera in 3 subfamilies. Several other sesquiterpene hydrocarbons, including Germecrene A, are also used by aphids as alarm pheromones. Aphid response to pheromones varies with species. Some jump or fall from their hosts, some disperse by walking, while others show a mixture of responses. Ant attended aphid species respond poorly to alarm pheromone depending more on protection from attendant ants than their own dispersive powers. Variation also occurs within a species, with alates being more responsive to pheromone than apterae, and adults being more responsive than nymphs. Alarm pheromones and their synthetic mimics hold promise for use in preventing aphid infestation of crops and reducing spread of aphid transmitted plant viruses.