SEX-PHEROMONE AND VISUAL TRAP INTERACTIONS IN MATE LOCATION STRATEGIES AND AGGREGATION BY HOST-ALTERNATING APHIDS IN THE FIELD

Field observations were made on the responses of males and gynoparae o f three host-alternating aphid species, the blackberry-cereal aphid, S itobion fragariae (Walker), the bird cherry-oat aphid, Rhopalosiphum p adi (L.) and the damson-hop aphid, Phouodon humuli (Schrank) to specie s-specific sex pheromones released from transparent and coloured water traps. Pheromone traps caught significantly more males than did contr ol traps without pheromone, whereas transparent, light green, yellow a nd orange traps caught most insects. Measurements of the distance over which sex pheromones function indicated that male P. humuli detect th e pheromone 2-6 m from the source and can fly upwind to a source in wi nd speeds of less than or equal to 0.7 m s(-1). In all three species s ignificantly more gynoparae were caught in pheromone traps than in con trol traps, suggesting that pheromone released by adult sexual females may assist late-flying gynoparae to locate a suitable host plant on w hich to deposit their progeny. The response is relatively stronger for males than gynoparae, but the pheromones appear to act as both sex an d aggregation pheromones.