It is well-known that Bactrocera oleae (olive fruit fly) females attract conspecific males by using 1,7-dioxaspiro[5,5]undecane (1) as the main component of their sex pheromone, and that 1 is produced in the female rectal gland. Although some authors have claimed that B. oleae males also attract females, to date no male-produced female attractants have been found in this species. In this paper, we report the first identification of a substance unique to males and able to attract females. The findings of the study include the following: (1) females responded in a bioassay to hexane extracts obtained from rectal glands of 15-day-old B. oleae males, (2) the presence of (Z)-9-tricosene (2) was consistently and unambiguously identified in these extracts using gas chromatography (GC) and GC-mass spectrometry methods, (3) in preliminary bioactivity tests, low doses (equivalent to a few males) of chemically and stereoisomerically pure synthetic (Z)-9-tricosene (2) attracted olive fruit fly females. Interestingly, compound 2, commonly called muscalure, is also a well-known component of the house fly (Musca domestica) sex pheromone.
The olive fruit fly, Bactrocera oleae, has a peculiar sexual chemoecology, guided by both male- and female-borne olfactory cues, mostly produced in rectal glands. Despite the research on B. oleae female pheromones has a long history, only few components (mainly 1,7-dioxaspiro[5.5]undecane) have been deeply investigated. Detailed evidences about the chemical identity and bioactivity of several others C10–C18 molecules produced in female rectal glands are lacking. We conducted GC and GC/EI–MS, identifying nine sex-specific chemicals and an additional compound [ethyl(Z)-9-octadecenoate], less abundant in females over males. Age-related production of all compounds raised over time. In 21-day-old females, it reached amounts from a minimum of 8.08 ng/fly (n-butyl dodecanoate) to a maximum of 87.19 ng/fly (ethyl hexadecanoate). In EAG experiments, all chemicals were perceived by both sexes. Methyl hexadecanoate and ethyl decanoate attracted males and females, respectively. This is the first report on a female-borne compound attracting conspecific females in Tephritidae. Our study sheds light on the bioactivity of female-borne pheromones involved in the B. oleae chemoecology. Further research is ongoing to test methyl hexadecanoate and ethyl decanoate as lures to enhance sex pheromone blends used in IPM programmes\ud
against B. oleae, thus improving control tools against this key pest
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