Abandoned in the garden

Many orchids have flower parts that mimic the shape and scent of female wasps. Mate wasps, beguiled and bamboozled by the impersonators, land on the flowers, unwittingly pick up pollen, and carry it to the next floral mimic--a classic example of how natural selection can make stooges of its protagonists, to the general amusement of biology students everywhere. But new research shows that the orchids' trick may not be so harmless as a simple practical joke, and that it is mostly the imitated females who pay the price.

Bob B.M. Wang of the Australian National University in Canberra and Florian P. Schiestl of the Swiss Federal Institute of Technology in Zurich measured how often male thynnine wasps visited patches of wasp-mimicking Chiloglottis orchids, compared with how often males visited genuine female thynnines, both inside and outside the orchid patches. The biologists observed that the males' visits to orchid sites decreased with time, suggesting that unrewarded males learned to avoid areas where the flowers proved deceptive.

But for the females--which are wingless and cannot readily change Location--the stakes were much higher. As the males learned to avoid the orchids, female wasps outside the flower patches soon had many suitors approaching them. Females within the suddenly unpopular patches, however, had few or no visits; in their case, a gorgeous surrounding was no thing of beauty. ("How an orchid harms its pollinator," Proceedings of the Royal Society of London B 269:1529-32, July 3, 2002)

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