The major component of the rectal glandular extract and volatile emission of maleBactrocera cacuminatus is racemic 1,7-dioxaspiro[5.5]undecane. l-Hydroxy-5-nonanone as its open chain form, together with 6-n-butyl-3,4-dihydro-2H-pyran are minor components. 1,7-Dioxaspiro[5.5]undecan-4-ol is present at a low level and is shown to be exclusively the diastereomer with an equatorial hydroxy group by comparison with synthesized samples of both epimers. Examination of the trifiuoroacetate by chiral gas chromatography has established the (4S,6S) stereochemistry (ca. 80% ee). The presence of 1,7-dioxaspiro[5.5]undecan-3-ol, or its isomerization product, 1,6-dioxaspiro[4.5]decan-2-ylmethanol, could not be confirmed. Trapping of the volatiles released by sexually mature male flies at dusk revealed that a number of the glandular components described above are released at mating time. Reexamination of the glandular secretion of sexually mature female olive flies (B. oleae) has failed to confirm the presence of any 1,7-dioxaspiro[5.5]undecanols, with the only volatile component (other than fatty acids) being 1,7-dioxaspiro[5.5]undecane.