moth question.

[Joseph G. Kunkel]

Pierre Bouillon wrote:
> ... 
> -question 1: in my humble opinion and experience, pupae cannot stand an
> actual freeze-out. Living cells (full of water) just explode and the
> chrysalis dies. However in some cases the chitine enveloppe is thick enough
> to prevent internal organs from being damaged. I even heard of some species
> "needing" the freeze-out to hatch properly...In most cases the caterpillar
> looks for a temperate location to pupate or dig a hole in the ground to
> burry the cocoon so that it doesn't freeze.

Pierre,

The field of freezing protectants in insects that over winter is well
known with publications starting at least back in the 1950s and
continuing until today. The following reference should include many of
the older citations:

Li N, et al. 1998.  Enhancement of insect antifreeze protein activity by
solutes of low molecular mass.  J Exp Biol. 201:2243-51. 

I worked in the lab of Jerry Wyatt who did some of the pioneering
research on this subject.  First, when cold weather approaches, over
wintering insects produce antifreeze substances including high
concentrations of glycerol which can accumulate in the bloodstream to
huge concentrations (20% is not unheard of) which protect the insects
from outright freezing in many cases. So insects do experience the low
temperatures in which all water we know of including sea water will
freeze.  Whether insects actually freeze depends on how much freezing
protectants they have accumulated by the time the low temps arrive.  The
giant silk moths, Saturniidae, tend to pupate in cocoons on the surface
of the ground or attached to twigs in bushes thus they certainly do not
burrow into the ground to avoid the freezing.

I am not aware of whether in the deep cold temperatures, which cecropia
and polyphemus and luna moths find themselves, that the freezing
protectants actually prevent ultimate freezing.  I do know that there
has been much laboratory research showing that some freezing protectants
act by preventing ice crystals from forming inside the cells.  One can
deep freeze _Drosophila_ embryos and tissue by freezing quickly.  Also,
crystals need a preexisting crystal nucleus to grow from.  Some
substances can inhibit the nucleation of crystals so that the cell water
freezes as a glass rather than a sharp edged crystal.  It is the sharp
edged crystals that kill cells by cutting through membranes and bursting
the cell as the previous respondent alluded to.  If you can avoid
crystallization during freezing you can be frozen and be revived.  That
is the basis for the new industry of freezing dying/dead humans in the
hope of storing them until a medical solution to their disease is found.

Joe
-- 
--------------------
Joseph G. Kunkel, Professor
Biology Department             joe at bio.umass.edu
University of Massachusetts    http://www.bio.umass.edu/biology/kunkel
Amherst MA 01003