Odour stimuli affecting autumn migration of Rhopalosiphum padi (L.) (Hemipter: ornoptera)

Summary R. padi gynoparae settling in the canopy of the winter host, Prunus padus , tended to form aggregations. Differences in the degree of exposure to wind, sun, etc., did not satisfactorily explain the aggregated pattern observed. In laboratory experiments, aphids did not distinguish between leaves taken from nearby aggregations and leaves taken far away from aggregations. The results of laboratory olfactometer tests and field trapping studies indicate that R. padi gynoparae produce an aggregation pheromone. Thus the aggregated settling pattern of gynoparae of R. padi can best be explained as a response to an aggregation pheromone.