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American Association for the Advancement of Science

Flower power and wasp-imposters

As the insect drinks the flowers’ nectar, it carries pollen from the male part of one flower to the female part of another flower.
[Image courtesy of Florian Paul Schiestl]

Full size image available here

Every day is Halloween for the Australian orchids that can put on a female wasp's costume. True, you might not see the costume, but a male wasp can. Scientists have discovered that this particular orchid gives off a certain sort of "smell" that's exactly the same one female wasps use to attract male mates according to research in the 17 October 2003 issue of the journal Science.

So why would an orchid want male wasps hanging around? Many flowers and insects have special relationships, in which they exchange certain favors for each other. As the insect drinks the flowers' nectar, it carries pollen from the male part of one flower to the female part of another flower. By dropping off the pollen, the insect "pollinates" the flower, allowing it to produce new seeds.

Some orchids get insects to pollinate them without offering a favor in return. The flowers do it by mimicking the shapes, colors and odors of the female insects, fooling the males into trying to mate with the orchids instead. In the process, the male insect pollinates the orchid.

Florian Schiestl of the Australian National University and his colleagues in Switzerland and Germany have discovered that an orchid called Chiloglottis trapeziformis needs only a single trick to make itself seem like a female wasp -- at least to male wasps. The plant releases a substance called a "pheromone" into the air, which is identical to the substance female wasps emit as a signal to get male wasps to mate with them. This pheromone is made up of just a single chemical compound. Why the orchid uses such a specific strategy is an evolutionary puzzle that researchers have yet to solve.


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