Metamorphosis Of Butterflies GEHP

[Joe Kunkel]

Pierre A Plauzoles wrote:
> 
> In a previous post on the butterfly newsgroup, you mentioned "ballooning of
> the larva" as a [dispersal] mechanism in the gypsy moth, which would then
> no longer need the use of wings to [disperse] itself.  Would you please
> explain what you mean by the use of this term? ...
Pierre,
The specific example of the gypsy moth (_Lymantria dispar_) dispersal is
an interesting one.  Gypsy moths are relative newcomers to the North
American continent. I will not tell their story of human borne
introduction from Europe into the New England area. In the old world
there are two major populations of gypsy moth, the Western European and
the Asian populations.  They overlap somewhat at the Ural mountains in
Russia. The two populations have different total strategies in their
life cycles based on the fact that in the Western European form the
female can not fly.  Asian female gypsy moths can fly.  The loss of
flight in the European form placed restrictions on how fast the species
can spread (disperse) from its current location.  If the female can not
fly then it must lay its eggs near the tree that its own mother's egg
was laid in or near.  The mobility of the flying male does not count
(much) in the specie's dispersal it just helps in keeping the genes
mixed up in the current area occupied by gypsy moths.
In the non-flying-female population the only substantial dispersal
occurs by ballooning.  The first instar larva, on hatching from eggs
laid at the base of a tree, walks up the tree and over perfectly edible
foliage and throws a line of silk into the air and balloons away down
wind.  That should have kept most gypsy moths in New England since the
winds generally go from West to East; but winds are fickle; and the
gypsy moth has slowly spread west and south so that it now threatens a
good part of the Mid Atlantic and Mid-West states and is pushing on
further. (Humans also transport egg masses on their campers and other
vehicles).
That was the mildly serious problem up until a half decade ago. 
Now, enter the Asian Gypsy moth.  Its female can fly as well as its
larva balloon.
The scuttlebutt about the Asian Gypsy told me as an apocryphal story by
a gypsy moth expert nicknamed Billy Bugs goes like so:
In Siberia and Asia the gypsy moth females and males feed on trees in
the valleys and after mating the adult female flies up into the
mountains and lays its egg mass in a rocky ledge.  On hatching, the
larvae must balloon down into the valley to reach the foliage they need
for food.  This cycle of female flying and larva ballooning is suggested
to have been selected for to avoid parasites.  Also one can note that it
is not primarily a dispersal mechanism in Asia but a life cycle
integrated into a survival scheme.
Sooo, after the wall came down and we began active trading with Russia,
the threat of the introduction of the Asian Gypsy Moth into the North
American continent became a possibility and now a reality since we have
had at least two incidents of Asian Gypsy Moth incursion, one on the
East Coast of the USA and one on the West Coast.  With flying female
gypsy moths the slow spread of the gypsy moth in North America could be
substantially accelerated.
You can read more about the problem by doing a search on Asian Gypsy
Moth on the Web.  I do some research on the problem which you can read
about at:
http://www.bio.umass.edu/biology/kunkel/asian.html
Joe
-- 
--------------------------------------------
Joseph G. Kunkel, Professor
Biology Department
University of Massachusetts at Amherst
joe at bio.umass.edu
http://www.bio.umass.edu/biology/kunkel/