Pheromones are a key reason many creatures, including humans, meet. In addition, while mating recognition systems in each species might be unique, pheromones are considered the important common denominator there also.

The mating 'language' is a key reason unacceptable mutants that use slightly different signals die off without any offspring. Even among moth species with different types of males and females, two different kinds of pheromones are in action, which was assumed to be the key factor in mate selection.

Not so, say researchers from the Institut National de la Recherche Agronomique, the Centre National de la Recherche Scientifique and the University of Toulouse. Pheromones are probably used for meeting, they contend, but they may not be used for mating.

Performing crosses and backcrosses between different pheromone races of the moth called the European corn borer, Ostrinia nubilalis, they obtained groups of individuals sharing the same pheromone type but differing in their overall genetic relatedness with the "pure" races, and, conversely, groups of individuals sharing a very similar genetic background but using different pheromones.

This species contains two types of females and two corresponding types of males: one type communicates with the so-called "E" pheromone while the other communicates with the "Z" pheromone. Although matings between these two types produce perfectly viable offspring, those matings very rarely mate in nature.

The former were expected all to show similar mating performances with a group of pure-race individuals - but they didn't. The latter were expected to show differences in mating success with pure-race individuals - but, again, they didn't. Therefore, overall relatedness rather than pheromone type seems a good predictor of the ability to mate, at least within this species.

Why, then, don't these mothy Capulets and Montagues mate more often?

That's a question for Shakespeare. Unless an answer is discovered in "Romeo and Juliet", biologists will have to continue searching on their own.

These results suggest that the role of pheromones in mating may not be quite as strong as previously thought, since another recognition system seems to coexist and constitute a powerful mating barrier.

Assortative Mating between European Corn Borer Pheromone Races: Beyond Assortative Meeting.Pélozuelo L, Meusnier S, Audiot P, Bourguet D, Ponsard S (2007)