A shift in the paradigm? A male-specific lactone increases the response of both sexes of the olive fruit fly Bactrocera oleae to the food lure ammonium bicarbonate

The olive fruit fly Bactrocera oleae (Rossi) (Diptera: Tephritidae) is a key pest species of wild and cultivated olive trees worldwide. Contrarily to most tephritid flies, in which males release the sex pheromone, in B. oleae the female is the sex responsible of attracting the opposite sex. However, and even though vast research has been done during the last decades, we are still far from understanding the chemical signals involved in the sexual communication of this species, including those produced by males. Here, we report for the first time the presence of two male-specific volatile compounds, namely ?-hexalactone and d-hexalactone, with the former exerting a significant attraction upon both sexes under laboratory and field conditions. Volatile collections conducted on laboratory-reared virgin individuals of both sexes revealed the presence of these two compounds only in males, regardless of their age. In double-choice behavioral assays, ?-hexalactone resulted to be attractive for virgin males and females (7-14 days old), with no attractiveness reported for d-hexalactone. Finally, in field assays traps baited with the binary blend of ammonium bicarbonate and ?-hexalactone yielded significantly more catches per week of both sexes than those baited with ammonium bicarbonate and ammonium bicarbonate plus 1,7-dioxaspiro[5.5]undecane, the major sex pheromone component. Altogether, our results shed light on the chemical ecology of the species and represent a promising experimental basis for the development of more innovative and effective mass trapping tools based on the use of ?-hexalactone.