Identification of Queen Sex Pheromone Components of the Bumblebee Bombus terrestris

We investigated the origin and chemical composition of the queen sex pheromone of the primitively eusocial bumblebee, Bombus terrestris (Apidae). Physiologically and behaviorally active compounds were identified by coupled gas chromatography electroantennography (GC-EAD), gas chromatography-mass spectrometry (GC-MS), and laboratory behavioral tests. In the behavioral assays, virgin queens frozen previously at −20°C were highly attractive to males. Dummies impregnated with surface and cephalic extracts obtained from virgin queens that had been frozen at −50°C were more attractive to males than odorless dummies. Male mating behavior was stimulated by components of cephalic secretions that are smeared onto the cuticle surface by the queen. Overall, 21 compounds present in surface and cephalic extracts evoked electroantennographic responses in male antennae. These included saturated and unsaturated fatty acids, ethyl- and methyl esters of the fatty acids, heptacosene, 2-nonanone, and geranyl geraniol. A blend of synthetic versions of these compounds elicited typical male mating behavior. Since solvent-impregnated dummies were approached by the males, but did not release copulatory behavior, visual cues may be important in the initial step of stimulating male mating behavior. Close-range olfactory signals are more important for releasing male mating behavior as well as for species recognition. In further behavioral assays, the attractiveness of a frozen virgin queen decreased as the storage time at −20°C increased from 2 hr to 1 d. Therefore, the chemical composition of the sex pheromone may change during freezing as behaviorally active compounds may decompose.