Field observations were made on the responses of males and gynoparae of three aphid species, Myzus persicae (Sulzer), Aphis spiraecola Patch and Ovatus crataegarius (Walker) to sex pheromone components, (4aS,7S,7aR)-nepetalactone and (1R,4aS,7S,7aR)-nepetalactol. The interaction between sex pheromone components and plant volatiles for field attraction of M. persicae was also investigated. Males and gynoparae of M. persicae were caught in significantly larger numbers in pheromone traps than control traps at sites with their primary or secondary hosts, but not at sites with their non-host plants. For males of M. persicae, the attractancy of sex pheromone components was enhanced by the addition of benzaldehyde, a major component of the volatiles from an extract of the host, Prunus persica. A. spiraecola males and gynoparae responded to the plant-derived nepetalactone, while O. crataegarious males and gynoparae showed no response to the nepetalactone (plant-derived or synthesised) alone but were attracted by the nepetalactol. Moreover, the attractiveness of nepetalactol to O. crataegarious males was significantly enhanced by addition of the nepetalactone. The female-produced compounds are shown to act as a sex pheromone for males and an aggregation pheromone for gynoparae, and the interaction of the sex pheromone with host plant volatiles is discussed.