Post-mating odor in females of the solitary bee, Andrena nigroaenea (Apoidea, Andrenidae), inhibits male mating behavior

We investigated odor changes and their behavioral significance in the solit ary, ground-nesting bee Andrena nigroaenea. We used gas chromatography with electroantennographic detection and performed behavioral tests with males in the field using natural odor samples and synthetic compounds. We found t hat only cuticle extracts of young females elicited copulation attempts in the males. We demonstrated that among the 17 compounds which triggered elec troantennographic responses, all-trans-farnesyl hexanoate and all-trans-far nesol were significantly more abundant in unattractive cuticle extracts of A. nigroaenea females. Dufour's gland extracts of these females also contai ned greater amounts of both compounds. In bioassays using synthetic farnesy l hexanoate and farnesol we found that these compounds inhibit copulation b ehavior in the males. Farnesyl hexanoate is probably synthesized in Dufour' s gland and used by females for lining brood cells. We interpret the semioc hemical function of farnesyl hexanoate and its precursor farnesol to have e volved secondarily. As an outcome of sexual selection, it facilitates the d iscrimination by males of receptive females from nesting and thus already m ated individuals. The dual function of these compounds represents an elegan t parsimony in the chemical communication system of this insect.