common names/systematics

[Pierre Zagatti]

dphowson wrote:

> Following this line of reasoning, does anyone know what is the isolating
> barrier that prevents Small White(pieris rapae) and Green-veined
> White(pieris napi) mating together? They are such closely similar species,
> are common in Europe, and fly together.

I don't know about these two species, but it has been shown on many Pierid
species
that visual identification (of species and sex) is mediated by UV reflectance
on wings. All these white butterflies show different wing patterns when seen
'through a male pierid eye', this allows the males to discriminate between
species, sexes and even old and newly emerged females.
Ron Rutowski has studied it extensively on Pieris, you'll
probably find references by searching from his name on the internet.
Another classical stuff in Pieris is the display of a rejection posture
by the female when she's not ready to mate or in the case of
an interspecific mating attempt (probably through the perception
of male courtship pheromones).

--
Pierre ZAGATTI
INRA Unite de Phytopharmacie et Mediateurs Chimiques
78026 Versailles Cedex
FRANCE
Tel: (33) 1 30 83 31 18
e-mail zagatti at versailles.inra.fr
http://www.jouy.inra.fr/papillon/