Volatiles of two chemotypes of Majorana syriaca L. (Labiatae) as olfactory cues for the honeybee.

A study of olfactory discrimination by honeybee has been set up in order to understand the role of volatiles of the aromatic plant Majorana syriaca in attracting pollinating insects. The honeybee's response to volatiles from leaves and inflorescences of two M. syriaca chemotypes, which differ in the thymol carvacrol ratio of their volatiles, was tested using a bioessay method based on associative conditioning and recruitement techniques. Behavioural data show that a honeybee identifies and reacts selectively to olfactory signals from leaves and from inflorescences of the two chemotypes. Such data suggest that the volatiles from all parts of the aromatic plant M. syriaca may have a role in attracting pollinators. The vegetative parts produce a volatile emission which attracts the pollinators from a distance towards the whole plant. At close range these are directed by the flower signal which is amplified by the volatiles of bracts and leaves in the inflorescence.