Migration?

[Bengt Lindqvist]

Anton Marais <u11674 at wpk.co.za> wrote in article
<Pine.SCO.3.91.980605121545.17614A-100000 at bisdev.wpk.co.za>...
>
> On Fri, 5 Jun 1998, Andrew Daw wrote:
>
> > >      I was wondering what drives butterflies and moths to
> > >      migrate (in this case northwards into southern UK),
> >
> <SNIP>
> >
> > In Europe for example, the Painted Lady (Cynthia cardui) is resident
> > in North Africa.  By early spring the local population has grown to a
> > point that the local habitat cannot support them, and they head off for
> > pastures new.
> >
> <SNIP>
> >
> > Being an African species a cold snap (overnight frost) can kill
> > them off quite easily compared to our more hardy resident species.
> >
> This is a very exciting topic - especially the migration of Vanessa
cardui!
> Here in South Africa we also get the Lady, but only during our Southern
> Winters. Probably because the foodplants only grow during this time as
> the summers are too hot! I have seen some Ladies in the mountains also
> and they seem to be migrating Southward!
> What I am therefore very curious about is if there has been any study
> into the migrating pattern of the Ladies.  Where did they originate
> from in the first place!  Is it really an African butterfly or could it
> be an American butterfly?  (Because there is some others in the same
> genus like Vanessa atalanta)
> Also: How did they manage to cross the Atlantic Ocean and when? (Probably
> before the break-up of the continents?)
>
> Regards
> Anton
I have some thinking about migration, not only long migration wich is done
by
V.atalanta and V.cadui. I wonder if the pressure from parasitic insects may
have
played an importent roll in make butterflies and mouth to migrat. Could you
imagen a better way to get rid of the parasit then to fly away 100 km an
seattled a new colony? I specially have in mind the geometrea D.blomeri and
P.ridens.
Both of them are known to suddenly show up in places long from the usually
spread of the the insect. And they both is known to be very commen on the
new
site. This is the situation in Sweden. I took these two as an example.


>