Jim T.,
I guess my earlier estimate of insecticide resistance in insects was too
low. The problem of resistance is not 'imaginary', and could be extremely
costly. The problem with hybrids is that they are designed for maximimizing
production. In addition to that, hybrids often are impacted by low levels of
pesticides which reduce the amount of secondary plant compounds which serve
as natural insecticides (terpenes for instance). Luxury consumption, and
irrigation often result in crops expending all the carbohydrates for the
production of stems and seeds. So when there are hybrids, very often the
insects, have a feast. With hybrids most of the plants, if not all the
plants, are genetically identical. This facilitates the insects which may
reproduce 3 or more times per year. Like viruses...they can 'evolve' much
more rapidly than the phenotype which is their host. In nature there are no
hybrids, thus the insect is not likely to 'feed equally' on all the plants
in a community. Just like the cold virus or the AIDs causing virus does not
kill or infect all humans who are exposed to these viruses.
Just think back during the time of the "Irish Famine". This famine resulted
from a pathogen which wiped out potatoes over a four year period. Over 1
million people died the first year. Finish people also died. The solution
was to import new varieties from Peru.
The use of corn hybrids and Bt corn is a ticking biological time bomb.
Remember when 40% of the corn crop in the SW US was wiped out? Well when
that happened, the solution was to import resistant corn from Argentina.
That saved the corn crop from being completely wiped out the following year
(cf. Altered Harvest).
Please read that 15 insects have alread developed Bt resistance. This is not
'imaginary' .....Also cornborers can develop 'moderate resistance' to Bt
corn.
chao
jf
http://www.extension.umn.edu/distribution/cropsystems/DC7055.html#ch11
Can European corn borer develop resistance to Bt corn?
European corn borer may have the potential to develop resistance to Bt Cry
proteins. Insects are known for their ability to rapidly develop resistance
to certain insecticides. Resistance occurs particularly when insecticides
are used repeatedly and at high concentrations. More than 500 species of
insects and mites have developed resistance to insecticides and miticides. A
recent Midwestern example in corn includes adult western corn rootworm
resistance to Penncap-M in Nebraska. In addition, laboratory colonies of
more than 15 different insect pests have developed resistance to Bt
proteins, including Indian meal moth, tobacco budworm, beet armyworm, pink
bollworm and Colorado potato beetle. Moreover, the diamondback moth, a
worldwide pest of cole crops, has developed high levels of resistance to Bt
insecticide in field populations in Hawaii and Florida.
Many factors contribute to the development of resistance. Some of these
factors for the European corn borer include: predictions for widespread use
of Bt corn, high season-long mortality, and two or more generations per
year. Recent laboratory studies in Minnesota, Kansas and Delaware confirm
that European corn borers (collected from Minnesota, Iowa and Kansas corn
fields) can develop moderate levels of resistance to Bt insecticides or Bt
Cry proteins (Fig. 14). Resistant European corn borer strains in these
studies require 30-60 times more toxin (resistance ratio) to kill 50% of a
test population of young borers compared with nonresistant European corn
borer strains. This modest level of Bt resistance developed in relatively
small lab populations after seven to nine generations of exposure. Although
these results confirm the genetic potential of European corn borer to
develop resistance, laboratory studies do not prove resistance will develop
under field conditions. Bt corn and European corn borers in the field pose a
dramatically different situation than larvae feeding on Bt insecticides in
laboratory diet.
Rumour will always out run truth, even on a muddy trail.
- Old Chilcotin
Saying # 89 -
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