What does it mean that target species don't get wiped out

[Paul Cherubini]

Michael Gochfeld wrote:
> 
> I don't agree with the example that since target species don't get wiped
> out by Bt we don't have to worry about non-targets. The target species
> are targets for a very good reason, intrinsic to their population
> biology and their potential for explosive population increase.  Most
> non-target species lack this potential at most times and in most places.
> Thus Gypsy Moths thrive in forests where certain species of butterflies
> might succumb.  This argument applies to any insecticide, not just Bt.

Do you know of any lep species that have been exterminated from a region
as a side effect  of regional spraying of Bt for gypsy moths?

Those of us in the chemical insecticide business don't see great species
to species variations in lep susceptibility to a given insecticide. In
other words, different chemicals quickly develope certain reputations
for their ability to kill certain classes of insects. So for example,
the insecticide Malathion developed a reputation many years ago as a
comparatively weak killer of the moth pests of orchard and row crops
(both the adults and caterpillars) and also turns out to be a weak
killer of stored food product moths like the Indian meal moth. Likewise,
it's a weak killer of butterflies like the cabbage white and alfalfa
butterfly.

By "weak" I mean a substantial percentage of lep insects survive each
treatment. I think alot of people have an idea in their mind that an
insecticide either "works" or the bugs have developed "resistance" to
the chemical. But a chemical may not "work" well ever, yet no resistance
has developed. It may be just be an inherently weak killer against a
certain (or all) classes of insects. An example are the "safer soaps"
you can buy at the corner store. Try wiping out a caterpillar
infestation on a large row crop acreage with one of those products. Good
luck. Ditto for diatomaceous earth.

Vapona (dichlorvos), on the other hand, has had a 30+ year reputation as
an outstanding killer of ANY lep (in the adult stage only) And little
resistance has been noticed after all those years of use. Vapona has
practically no registered uses in agriculture, however.

 Even our most powerful insecticides - the deadly space and soil
fumigant gases like phosphine and methyl bromide- rarely give a 100%
kill of all life stages in treated warehouses that are tightly sealed
for several days at a time.  Retreatments are often needed in just a few
months as survivors multiply.

So what I'm getting at is that Bt has not developed a reputation as a
particularly powerful lep killer and if alot of gypsy moths survive
successive treatments, it is highly likely that alot of non-target leps
will also survive. In my opinion, this fundamental characteristic of Bt
may partially account for the reason the ag chemical community is not
behaving as though they are worried that  Bt corn pollen is capable of
having any significant non-target lep killing potential. They've known
that for years. 

The Cornell monarch butterfly researchers could have learned that too if
they had taken a few days time to interview some of the many hundreds of
licensed, scienced degreed agricultural pest control advisors that work
for large corn farms, chemical and seed companies in the MidWest. These
experts are out monitoring corn fields 6 days a week all summer long,
year after year. But when a professor thinks to him or herself about
where to find out specialized information about the real world efficacy
of a pesticide, does he/she think about driving over to the local Ag
chemical dealer and talk to the ag pest control advisors working there?
No, they consult fellow professors in fields such as crop science who
are unlikely to have acquired the depth of real world knowledge of
specific pesticides that actual advisors and applicators have obtained.

The consequences of this situation are that if you talk to practically
any average citizen who has read a newspaper story about the Cornell
report they will say "yeah I've heard the monarchs in Kansas are all
dying". 

Paul Cherubini, Placerville, California