Overwintering Hawk Moths?

Jeffrey A. Caldwell ecosys at pacbell.net
Mon Oct 2 02:20:33 EDT 2000

"Martha V. Lutz & Charles T. Lutz" wrote:

> 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

I am glad to see you thought of that! I believe that light pollution is having
enormous impacts that nobody even thinks about. I wonder how many people doing
"environmental impact statements" are taking it fully into account?

About ten years ago I did some studies of environmental impacts of  running a
six lane freeway over a stream. When I pointed out that the portion of rocky
stream under the freeway underpass would be so deeply shaded that it would be
like a cave, with no green algae and a loss of aquatic biological productivity,
everybody said that particular shading impact had never been considered before.

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