Overwintering Hawk Moths?

[Martha V. Lutz & Charles T. Lutz]

EE from Toronto, ON, wrote:

"Today I found a GIGANTIC tomato hookworm on a tomatillo plant. I must
admit that last year I offed a whole generation of them early in the
summer with my garden shears. But this one is just too big to kill and
it's the end of a pathetic growing season anyway.

...

How would one overwinter such a creature? Do I provide a pot of dirt?"


This caught my eye because while at the outdoor track this past Wednesday I
found an adult Manduca quinquemaculata.  I also found a larval Pyrrharctia
isabella (in lane six, doing an all-out caterpillar sprint).  Both visited
a local elementary school with me on Friday, where I pointed out to the
students that although finding a woolly bear caterpillar is not unusual in
Iowa at the end of September, the adult moth (Manduca) is a little less
common at this time of year.  We talked about possible reasons for an adult
of that species to be on the wing this late in the year.  While we were
discussing this, a somewhat unpleasant hypothesis came to me . . . is it
possible that this is an effect of light pollution?


Presumably the Manduca larvae use daylength (shortening) as a cue to enter
diapause (as a pupa, underground) rather than emerging as adults to start
another generation.  In the past few years I have found a very few newly
emerged moths (of a variety of multivoltine species) late in the summer or
early in the fall, and always assumed that it was simply genetic variation
that could potentially allow expansion of the local population into
Southern parts of the species range.  Adults that emerge too late for their
offspring to have any chance of completing larval development before the
leaves fall and the weather turns cold are evolutionary zeros (as in zero
fitness), so I assumed that they were maintained in the population by some
other selection pressure, and that migration played a role in this.  Maybe
I have been wrong about this.

Is it possible that these adults were, as larvae, exposed to outdoor
lighting that artificially extended their 'days,' so that the daylength
they perceived indicated that another generation would be successful, while
the real daylength was shorter and would have initiated diapause?

That's a long and awkward sentence, but I'm short on time, so rather than
editing I'll just ask the list whether anyone has any thoughts about light
pollution as an explanation for late summer larvae of multivoltine leps
failing to enter diapause and emerging as adults with no chance of
successful reproduction?


In Stride,
Martha Rosett Lutz


P.S.  I would also like to 'plug' the idea of taking insects into grade
school classrooms.  Even if you don't have a pre-planned presentation, just
taking some insects in for 15 minutes or so does a world of good!  The kids
are alert, excited, interested, and have infinite questions.  They love to
touch the insects, learn about them, and enter into discussions about
evolution, behavior, and anything else the adult has to offer!  Walk in the
door of an elementary school classroom with a cage of insects and you will
have the most eager, attentive audience imaginable--with enough questions
to keep discussion going as long as you can stay on your feet (or longer)!