Female leaf-cutter bees are choosy about their sexual partners: They only fall for males who give off the appropriate smell.
Zoologists at the University of Bonn's Institute of Agricultural Zoology and Bee-Keeping have discovered that the male bees actually have to rub their scent under their partners’ noses. Glands in their front legs serve as “scent sprays.”
There is not much room for sensuality in the sex act of the leaf-cutter bees. The male throws himself on the female, gets a firm hold on her feelers with his jaws, keeps her eyes shut with his forelegs, presses her wings against her body with his middle pair of legs and forces her abdomen upwards.
“But the lady bee alone decides who she would like to mate with,” Professor Dieter Wittmann explains, “if she doesn’t want her suitor, she bucks and throws him off - and sometimes even shows him who’s boss with her sting.”
Above all it is a cocktail of scents produced by the male in his abdomen and spread around the place where they rendezvous which decides whether the suit is a success or failure.
“This cocktail of scents presumably enables the female to recognize whether she is related to her potential sexual partner or not, thus avoiding incest,” Professor Wittmann explains.
If the male has been successful in attracting a female, he clings to her neck and jams her feelers between the hook-like teeth of its powerful jaws. While this is happening, the feelers are bent so that they are lying on the male’s forelegs.
The forelegs of male leaf-cutter bees reveal mysterious structures: One of the tarsi is extremely enlarged and has a scoop-like protuberance.
While evaluating the video recordings, Professor Wittmann and his team discovered that shortly before copulation the female’s feelers are placed in the curved blade of the scoop. In the examination by electron microscope they also discovered that the scoop blade is pockmarked with tiny holes, the outlets of scent glands.
“The curved scoop-like shape serves the male as a ‘hand spray’ with which he sprays the feelers of his partner - her nose - with his sexual scent.” At the same time, the male bee places his forelegs, which in part are translucent, over his partner’s eyes, thereby creating a species-specific pattern of light and shadow.
The complex procedure probably acts as a kind of passport control: The males look about every 90 seconds to see if a female is waiting at the rendezvous spot. However, in their absence, rivals attempt to get off with the females who have been lured there. By means of the “scent spray,” the female can compare the scent of the rendezvous area with that from the forelegs, thereby checking whether she is being taken for a ride by a fraudulent suitor.
Professor Wittmann and his team have been able to prove the existence of similar mating mechanisms among other bees and even wasps. Thrilled, he says: “A miniature world of seduction is unfolding, which we never suspected these little insects to be capable of.”
In some species, the lady bee can only get in the mood if there is the right combination of scent, light and soft caresses - some scent sprays are equipped with thousands of fine hairs, which can gently massage the female’s feelers.
Graphic depicting the process described above (according to the cutlines in German. Translation by AltaVista's Babel Fish.)