diapause / voltinism

[Martha V. Lutz & Charles T. Lutz]

Kurt Jacobs" <morphidae at earthlink.net> wrote:

"Some species of lepidoptera are univoltine. I believe univoltine means they
can diapause, but someone needs to define this word, as its not in my
Websters"


Univoltine means one generation per growing season (usually summer); i.e.
one generation per year. Hyalophora cecropia is an example of a univoltine
species.   Multivoltine means more than one generation.  Actias luna is
univoltine in the Northern parts of its range, but multivoltine in the
Southern parts.  Monarchs (Danaus plexippus) are multivoltine.

As for diapause:  right from an exam I wrote for Dr. David Stanley's course
at UNL (Nebraska) last fall:

        Diapause is an assemblage of phenomena, both physiological and
behavioral, that serve to synchronize the life cycle of an insect species
with predictable seasonal changes in its environment.  The unifying feature
of diapause is that it is a genetically hard-wired phenomenon triggered by
token stimuli; for example, alterations in day length.  In any given
insect, diapause occurs during a species-specific phase of the life cycle,
proceeds according to a 'programmed' plan, and continues until it has run
its course.  Generally characterized by reduced metabolic activity and
suppressed reproductive behavior, diapause prepares insects to meet
approaching environmental changes.  Both the physiological control and the
visible manifestations of diapause are as complex and diverse as the many
species, life cycles, and different environments of insects.  Diapause
confers on an individual insect a higher probability of surviving
predictable adverse environmental changes, and thereby mediates
evolutionary adaptation of that species.
        Diapause is controlled by neurohormones.  Token stimuli in the
environment cause alterations in neurohormone titres, which in turn induce
the diapause syndrome.  Diapause is species-specific both as to its timing
within the life cycle and its manifestations.  However, some species may
exhibit plasticity, particularly their response to stimuli that break
diapause.
        For example, Gypsy Moth eggs have an obligate diapause of 180 days.
No known stimuli will alter this requirement; there is apparently no
plasticity.  By contrast, luna moths have a pupal diapause phase which does
exhibit plasticity.  Actias luna, a multivoltine Saturniid, has a prolonged
pupal diapause that allows it to survive the inhospitable Iowa winters.
Ecdysis normally takes place in late May or early June.  Cocoons brought
indoors in March will hatch in concert after about three weeks-allowing the
moths and their offspring to attend classes in local grade schools.
        Saturniid adults are short-lived and do not feed and; they must
reproduce soon after emergence, or die with a fitness of zero.  Winter
dormancy implies a need to coordinate adult emergence so that mating is
possible.  Synchronizing ecdysis via ambient temperature increases the
probability that diapausing pupae experiencing the same weather will emerge
together and live happily for long enough to mate and lay eggs.


///

Or, put another way:

There is a key to understanding things like diapause:
first, it is pre-programmed; second, it has cause-
called token stimuli, but please don't mind the name.
It just means things like:  day lengths that do not stay the same.
As days get shorter (past mid-June) a luna larva 'knows'
this heralds colder weather.  Maybe even snows.
It must survive the winter to frolic in the spring.
How is this done?  Please see line one:  diapause is the thing
that triggers many changes (like glycerol in the 'blood,')
to make our little larva ready to get snug.
Certain neurohormones secreted in the brain
control the way our little friend will wander the terrain
and spin a cozy hermitage, a silvery cocoon,
a refuge against winter wind, cold dry air, and gloom.
What heralds spring?  Not day-length.  The token now is heat;
a subtle warming trend foretells winter's slow retreat
from roots and twigs and buds.  Our luna counts a sum
of degree-days.  The moth debuts.  And diapause is done.



Hope this helps.

In stride,
Martha Lutz