regal eclosion again

[felger at CCIT.ARIZONA.EDU]

> I got almost no response to my query about the environmental cues
> that regal and imperial moth pupae use to know when to hatch.
> One person suggested that even though they are many inches underground,
> they still somehow receive light.  I can hardly believe this is
> possible, but perhaps the pupa wriggles closer to the surface to
> get light?  I have no idea.


I have many thoughts and observations regarding eclosion/developments cues
for subterranean pupae.  Someday I might even spend time again looking up
literature on the subject (hah!)

Art Shapiro has a couple of papers on barometric pressure affecting
emergence of butterflies.  I can't find these immediately, you might
contact Art, or use BioAbstracts or other indices to find these articles.
As I recall, (apologies in advance for misinfo), I think he was
hypothesizing that increasing barometric pressure may assist the insects
in breaking out of their chrysalids.  I believe the results of the work
were not conclusive.

I believe, as do a few of my colleagues, that barometric pressure
fluctuations may be one 'cue' that pupae might detect.  All of us have
many anecdotes about "difficult" moth pupae which "hold over" far too
long, suddenly emerging with freak weather events, such as thunderstorms
on the California coast.  I have attempted and failed to induce early
emergence (February-March) for Citheronia splendens by simulating an
abbreviated year (graded photoperiod) and then keeping the pupae warm and
humid for weeks.  The results are discouraging, even with 18 hour days and
a more or less normal (simulated)dusk and dawn.  Although there were 1 or
2 emergences in May, the remainder of approx 40 pupae emerged at the same
time the untreated pupae emerged--namely June, July. Certainly, just
maintaining high temperature and humidity is a waste of time for certain
species.

It seems obvious to me that insects have internal clocks which we have
simply not begun to understand.  I believe that (for some species, at
least) a sequence of events (which may be complex) must occur to induce
emergence. 

Perhaps we should send a few of these pupae to some of our colleagues
in the southern hemisphere to observe.  That is one thing I have not done,
yet.

Certainly, ceratocampines do not have the translucent cuticle patches on
the head that some saturniines have. And as you detected, it does not seem
reasonable that a pupa buried four inches or more below the surface of the
soil can detect light.  

MFW