Comparative responses of parasitoids to synthetic and plant-extracted nepetalactone component of aphid sex pheromones

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.