Pseudocopulatory pollination in Lepanthes (Orchidaceae: Pleurothallidinae) by fungus gnats

Gnatty answer to pollination puzzle

It is well known that many orchids are pollinated by male insects that attempt to mate with the flowers. In the great majority of these insect-deceiving mechanisms, the pollinia are transferred during the pre-copulatory behaviour of the male; copulation itself does not occur. However, an extreme form of this rewardless or deceit pollination has been described in an Australian orchid genus, Cryptostylis: pollinium transfer only occurs during the actual act of copulation, hence the process is termed genitalic pseudo-copulation. But is it confined to Cryptostylis? The answer, provided by the work of Mario Blanco and Gabriel Barboza (Gainesville, Florida and Puntarenas, Costa Rica, pp. 763�772), is clearly �no�. These authors have worked with a tropical orchid genus, Lepanthes, which contains over 800 species. The authors describe Lepanthes species as epiphytes with tiny, brightly coloured and complex flowers that offer no reward to pollinators. The latter feature, combined with the floral structure, suggests that pollination occurs via sexual deceit but until recently there had been no confirmation of that. However, one of the authors had noticed that the flowers are visited by male fungus gnats and this led to detailed observations of insect visitations. The authors have obtained beautiful pictures of sexually aroused male gnats �mating� with the flowers of L. glicensteinii, showing clearly that the pollinia are transferred to the gnat during genitalic pseudo-copulation, with evidence in some visits of actual ejaculation by the gnat. The relationship between the gnat, which itself was a newly described species, Bradysia floribunda, and the orchid appears to be species specific. This paper thus illustrates beautifully the value of careful direct observation on living plants. Further, Lepanthes is a very large genus and the similarity of the flowers across the genus suggests that it is possible, even likely, that this type of deceit pollination may be more common than previously thought.