Chemical communication in the Mediterranean fruit fly Ceratitis capita (Wiedemann)

In the present study the newly-identified `Medfly' sex pheromones have been bioassayed. Three olfactometers with airflow and two sizes of horizontal wind-tunnels have been developed. The bioassays without airflow were carried out in a bioassay chamber in the laboratory and the insects were caged with citrus plants in a mating behaviour study in semi-natural conditions. Trapping studies were carried out in a greenhouse, culture rooms, and in citrus orchards of southern Spain.The males of C. capitata (Medfly) release from their abdominal tips a volatile sex pheromone which attracts virgin females. There is a significant correlation between male `calling' and female `landing' which are important components of the sequence of sexual behaviour. The calling male occupies the lower surface of a citrus leaf, releasing sex pheromones, which have two main functions, one is to attract other males to form a `lek' or mating assemblage and the other is to attract females to the `calling' males prior to mating.Experiments were carried out in which medflies of both sexes were exposed to natural pheromones released from live males of the same species and to volatile components of the pheromone formulated in various substrates. Both sexes were also assayed against extracts of males and against various synthetic attractants including the compounds 3,7-dimethyl-1,6-octadiene-3-ol, linalool; 2,5-dimethyl pyrazine; 2,3-dimethyl pyrazine; geranyl acetate; E-2-hexenoic acid; ethyl palmitoleate; α-farnesene, furfuryl alcohol and others. The components were tested singly in various doses, and in various combinations.Some of the above compounds were shown to enhance long-range attraction, inducing females to perform upwind flights toward the source of the attractant, while the other components induced short-range attraction. Certain components, e.g. linalool, elicited specific sexual behaviour from both sexes. Linalool was shown to be a multifunctional sex pheromone component, producing certain sexual responses in both male and female medflies.Preliminary field trials in citrus orchards in southern Spain using vertical white and yellow sticky traps were encouraging in that they demonstrated that, under certain conditions, relatively high catches of males and females could be obtained with linalool acting alone or in combination with other pheromone compounds.