Photos of urban monarch overwintering sites California

[Stanley A. Gorodenski]

>
> I've never heard of any insecticide that was known to substantially
> reduce the fertility or fecundity of any lepidopteran due to
> field exposures in the adult stage. The inventor of such a hypothetical
 
Paul,
In your response you appear to recognize that there is some effect of
pesticides on the fertility and fecundity of adults: "I've never heard
of any insecticide that was known to substantially…".  You may not have
really meant to say this, and so a question, which may be basic to the
physiology of the Monarch (or lepidoptera in general), is whether some
chemicals can reduce fecundity or fertility of adults.  It seems
reasonable that this can be, and so I will continue under the assumption
that there can be an effect, unless someone more expert in this area can
correct it.
 
You said "I've never heard of any insecticide that was known to
substantially reduce the fertility or fecundity … in the adult stage".
I think a  problem in this case is determining what is a substantial
reduction.  It would depend on the species, and one would have to take
into account the effect of any reduction in fertility or fecundity on
the long term survival of a population.
 
Also, the effect of a pesticide or chemical application in a field crop
situation (such as a cotton field) on a Bollworm moth, for example, may
not be the same as the effect on a species like the Monarch during
overwintering conditions in urban areas.  The chitinous exoskeleton may
be a good barrier against casual exposure to a chemical in the Monarch
and probably would not affect fecundity or fertility.  However, I think
the life history of the Monarch, compared to that of the Bollworm moth
(for example), may increase the probability of small traces of chemical
applications getting inside the butterfly before oviposition and,
thereby, affecting fertility and fecundity.
In a cotton field, a Bollworm moth emerges, mates, and lays eggs
relatively quickly before it has a chance to ingest nutrients that may
be tainted with chemical applications.  Thus, one would not see much of
a reduction in fertility or fecundity in field conditions and this
supports your statement: "I've never heard of any insecticide that was
known to substantially reduce the fertility or fecundity of any
lepidopteran due to field exposures in the adult stage".  In fact, some
moths don't feed at all as adults (is the Bollworm moth one of them?).
 
The Monarch, in contrast, has a long lifespan compared to the Bollworm
moth.  There is a considerable length of time before ovipositing the
following year which may increase the chances of the adult ingesting and
building up chemicals (either through contaminated nectar or water
puddles) that could affect fertility and fecundity.
 
I am still not convinced that the urban environment is hospitable to the
Monarch.  It may be, and all the photographs and facts you have
presented merely reflects that (as I said before, what you have
presented does seem to indicate the Monarch is "thriving" and, on the
surface, all the anecdotal information supports it), but from a strict
scientific point of view I have not seen references (in this forum) to
the definitive studies that establish it.  I feel the area of urban
ecology needs more study before such conclusions can be drawn (my
opinion only).
 
Stan
 
 
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