none The responses of aphid parasitoids to completely synthetic and plant-extracted nepetalactone, a component of aphid sex pheromones, were investigated. In wind tunnel tests, Praon volucre and Aphidius ervi responded equally strongly to both plant-extracted and 99% pure synthetic (4aS,7S,7aR)-nepetalactone. In the field, aphid-infested cereal trap plants were used to test the attractiveness of plant-extracted and synthetic (4aS,7S,7aR)-nepetalactone, as well as the synthetic enantiomer (4aR,7R,7aS)-nepetalactone. There was no significant difference in parasitisation levels by Praon spp. between plants baited with the synthetic or with the plant-extracted 7S isomers. However, the 7R isomer was unattractive alone and rendered the synthetic 7S isomer unattractive when combined to form a 50% blend of the two. It is concluded that the response of aphid parasitoids to nepetalactone is influenced more by enantiomeric purity rather than the possible presence of plant-related contaminants associated with plant extraction. The results are compared with data on male aphid responses to the compounds, which indicate that plant-derived contaminants can reduce attractancy, and the implications for the manipulation of parasitoids in the field are discussed. Sensory reception; Behaviour; Communication; Chemical signals; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts; Abiotic factors; Land and freshwater zones; Palaearctic region; Europe; United Kingdom Aphidius ervi; Praon volucre (Aphidiidae ); Chemoreception; Hemipteran host sex pheromone component; Synthetic vs plant derived comparisons; Hemipteran hosts; Parasite response to host sex pheromone component; Synthetic vs plant derived extracts; Chemical factors; Synthetic hemipteran host sex pheromone component; Comparative responses, control potential, field & laboratory study; England; South; IACR Rothamsted; Responses to hemipteran host synthetic/plant based sex pheromone components Acyrthosiphon pisum; Sitobion avenae (Aphidoidea ); Chemoreception; Synthetic vs plant derived sex pheromone component; Hymenopteran parasitoid response comparisons, control potential; Pheromones; Sex, nepetalactone component; Hymenopteran parasite responses to synthetic vs plant extracts; Hymenopteran parasites; Parasite response to host sex pheromone component; Synthetic vs plant derived extracts, field & laboratory study; Plant hosts; Plant derived nepetalactones, sex pheromone incorporation; Responses by hymenopteran parasites, synthetic extract comparison; England; South; IACR Rothamsted; Hymenopteran parasite responses to sex pheromones; Plant derived vs natural extract comparisons, control implications