Bt resistance

Wayne M. Barnes, Ph.D. barnes at BIODEC.WUSTL.EDU
Sat Feb 4 12:59:01 EST 1995

On Fri, 3 Feb 1995 23:20:26 -0600, 
Neal Stewart (nstewart at wrote:

>I believe this view is fallacious.  When strong selection pressure is 
>applied (high levels of Bt expression) then insects will evolve at a 
>*faster* rate.

    My point is that the insects have to survive to evolve, and the 
companies' trangenic Bt genes are so strong, they don't allow enough 
survival for evolution.  

>        Another wrinkle in this story is that not all lepidopterans are 
>equally susceptable to Bt, for example Heliothis virescens is susceptable 
>and its relative Helicoverpa zea is fairly resistant.  Even if Wayne's 
>hammer analogy was true, then you would only be hitting Helicoverpa zea with 
>the comic section of a daily newspaper.

      'Fairly resistant' is not enough.  It just so happens that you 
mentioned 2 of the 3 insects that I have tested my weak 'academic strength' 
Bt gene against, and it did fine:

Hoffmann, M., Zalom, F.G., Wilson, L.T., Smilanick, J.M. Malyj, L.D.,
Kiser, J., Hilder, V.A., and Barnes, W.M. (1992)  Field evaluation of
transgenic tobacco containing genes encoding Bacillus thuringiensis
delta-endotoxin or cowpea trypsin inhibitor:  Efficacy against Helicoverpa
zea (Lepidoptera: Noctuidae), J. Econ. Entomol. 85, 2516-2522.  

      The 'industrial strength' genes of i.e. Monsanto, being composed of 
synthetic, plant-preferred codons, are 100 times stronger.  The bacterial 
codons, using usually A,U in the 3d position, are expressed poorly in plant 
cytoplasm, worse in some plants then in others.

    Actually, 50-100 times stronger is their conclusion.  When I read their 
paper and did my own math from their data, I came up with 1000 times better!

Barnes at    -------------------------
Wayne M. Barnes, Ph.D.             fax: 314/362-7183
Dept. Biochemistry 8231, Washington Univ. Med.School
4566 Scott Avenue
St. Louis, Missouri 63110 USA       ph: 314/362-3351

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