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The honey trap
Those familiar with ‘Old World’ orchids know that many species attract pollinators by means of sexual mimicry. Indeed, in some species, having been lured by the false promise of sex, the pollinator receives no reward at all because the flowers do not even provide any nutrition. However, rather fewer instances of sexual mimicry are known amongst ‘New World’ orchids and it is thus interesting that such mimicry has now been described in the Central American epiphytic orchid, Mormolyca ringens. Singer et al. (Campinas, Brazil, pp. 755–762) describe the flower (particularly the labellum) as being similar to those of Ophrys, an Old World genus in which sexual mimicry is widespread. Further, the flowers produce a complex of volatile compounds that add to the sexual mimicry, by acting as a pheromone. Indeed, drones (males) of a particular bee species, Nannotrigona testaceicornis, exhibit a strong positive response to these volatile compounds and these drones are, not surprisingly, the most common pollinators. The drones become sexually excited and attempt copulation with the flowers. This, of course, is unsuccessful but there is a nutritional reward in the form of starch and lipids. Then, as the drone backs away from the flower, he picks up the pollinarium. At this point, the drone may visit another flower on the same plant, resulting in a self-pollination or may visit flowers on another plant. However, preliminary studies with manually pollinated plants suggest that Mormorlyca ringens is not self-fertile. Thus, his visit is fruitful only if he moves on to another plant. The final point for comment is the compatibility of the floral ecology with bee biology. Flowers are produced throughout the year and are thus always available for the drones, which occur in large batches several times per year. The flowers, cleverly, are able to attract drones before the real females appear.Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
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