Electrophysiological and behavioural activity of plant volatile terpenes in three tephritid flies

Rhagoletis cerasi (L.), the European cherry fruit fly, Ceratitis capitata (Wiedemann), the Mediterranean fruit fly, and Bactrocera oleae (Rossi), the Olive fruit fly, (Diptera: Tephritidae), are the most destructive tephritid flies in European fruit production. Their control still relies on broad spectrum insecticides which are toxic to natural enemies of flies and non-target organisms. Therefore, improved detection tools based on semiochemicals for monitoring both sexes of the fly populations are needed to enhance environmentally safe control methods. This study aimed at understanding the biological role of four ubiquitous plant volatile terpenes, (a)-(-)-copaene, (b)-(-)-pinene, (R)-(+)-limonene, (S)-(-)-limonene, previously identified as behaviourally active compounds for the three tephritid species. In order to verify the olfactory sensitivity of the three flies to the plant terpenes EAG doseresponse curves were recorded on both males and females (5 doses from 0.25μg to 2.5mg of the synthetic compounds diluted in mineral oil). Moreover, field tests were carried out in infested fruit growing areas of southern Italy deploying white sticky tablet traps baited with rubber septum dispensers loaded with 1 mg and 10mg of the compounds. All tested substances evoked dose-dependent EAG responses in both sexes. In R. cerasi all the terpenes elicited similar significant EAG responses; traps baited with (b)-(-)-pinene, (R)-(+)-limonene and (S)-(-)-limonene caught significantly more males than those of control. In C. capitata (a)-(-)- copaene showed both the highest EAG responses and the number of males caught in the field. In B. oleae (R)-(+)-limonene and (b)-(-)-pinene induced EAG responses similar to those of the sex pheromone and significant trap catches were found of both sexes. This work confirms that plant volatile terpenes are involved in host-plant location by tephritid fruit flies and indicates that they are likely to improve the current strategies for predicting the timing of management decisions against these pests.