CEREAL APHID RESPONSES TO SEX-PHEROMONES AND HOST-PLANT ODORS IN THE LABORATORY

The movement of Sitobion fragariae (Wlk.) (Homoptera: Aphididae) males towards odours from conspecific sexual females (oviparae) and the aph id sex pheromone component (4aS,7S,7aR)-nepetalactone were demonstrate d in a linear-track olfactometer Males of the closely related Sitobion avenae (Fab.) were attracted to odours from conspecific oviparae and also oviparae of S.fragariae. These results were consistent with the r ecent identification of this nepetalactone isomer as the major compone nt of the sex pheromone in these species. Males of S.fragariae were no t significantly attracted to oviparae of S.avenae, indicating some qua litative or quantitative difference in the pheromones of the two speci es. Males did not respond to the related (1R,4aS,7S,7aR)-nepetalactol or to host-plant odours. Gynoparae of these species moved towards the nepetalactone and also to host-plant odours. A combination of both sti muli was more attractive than plant odour alone. Gynoparae of S.fragar iae also responded significantly to the combined treatment when this w as tested against the nepetalactone.