14 DAY TRIAL // A new study suggests that orchids exploit male bees for their own purposes by imitating the scent of bee females. This little trick played by orchids relies on the instinctive urge of male bees to mate when detecting the scent of a female insect. As the male falls in the trap set by the orchid, its attempt to procreate ultimately ends by pollinating the orchid.
The same study also points out that some of the scents emitted by certain species of orchids have an effect so powerful that bee males ejaculate on the flower. Male bees are attracted by females pheromone chemicals released by the latter. Pheromones are chemical signals used by both insects and mammals as a sexual attractant.
By studying the pheromone variations of 15 populations of Colletes cunicularius bees and the orchid that mimics it, Ophrys exaltata, Nicolas Vereecken along with Florian Schiestl from the University of Zurich, discovered that the pheromones emitted by the orchids were only slightly different from those released by female bees in different populations and that orchids use this sexual trick to their own advantages.
"This was not at all what we expected. If the orchids thrive on imitating female bees, the match should be as perfect as possible", says Schiestl.
To explain why the scent of the orchids is not identical to that of female bees, the two researchers suggested that bees may also suffer the effects of inbreeding, therefore their mating with individuals from other populations may provide the perfect opportunity to enhance the genetic variety. It seems that male bees do indeed feel more attracted to slightly different pheromone scents, therefore cannot make the difference between that of an orchid and that of a female from another bee population.
The results of the study show that 50 percent more bee males visit orchids with pheromone mixes slightly different than those of the females in their population and even more those orchids with greater differences in the pheromone mix - up to five times more males. By altering the natural scent given off by orchids, the bee male attractiveness nearly doubles.
"When outbreeding is desirable, it makes sense for males to look for females with exotic scent. But in this case, what they find instead is the orchid", says chemical ecologist Manfred Ayasse at the University of Ulm.