May 6, 1999
Prof. Joe Cummins
e-mail: jcummins@julian.uwo.ca
New study shows that the refuge strategy for Bt resistance *hastens* spread
of insects resistant to corn borer!
Millions of acres of corn bearing genes for Bt toxins that poisons corn
borer insects have been planted in the United States and Canada. This year
Canada implemented requirements and the US recommends planting blocks of
corn without the Bt resistant corn to provide a 'refuge' where wild type
corn borer insects will thrive.
The theory is that mutations will take place in the insects making them
tolerant of the Bt toxin. It is assumed that all resistance will be
recessive so that when the mutant mates with the conveniently available
wild borers the off-springs will all be sensitive to toxin and die when
feeding on the genetically engineered Bt corn.
However, if some dominant Bt mutants appear among the Bt tolerant insects
those mutants will spread their genes by mating in the refuge and their
off-springs will thrive on the genetically engineered Bt corn.
The appearance of dominant borer mutants would create a disastrously
rapid spread of borer resistant mutants because the refuge would provide a
rich breeding ground for the resistant mutants (dominant mutants appearing
in fields with out a refuge would have a long search for borers to mate
with).
This weeks Science (May 7,1999:965-967) "Inheritance of resistance to
Bacillus thuringiensis toxin (Dipel ES) in the European Corn Borer" Haung,
F., Buschman, L., Higgins, R. and McGaugen, W. report shows that dominant
mutants conferring resistance to Bt toxin can be recovered from Corn Borers
exposed to the toxin.
Such mutants would spread like wildfire through corn fields with refuge
plots because over half the off-springs of mating between mutant and wild
type insects would be resistant to Bt toxin.The refuge would provide a rich
breeding ground for spread of the dominant mutants.
The reported finding of dominant Corn Borer mutants should be enough to
call a moratorium on the use of Bt corn.
Furthermore, the required use of the dangerous refuge concept has often
been promoted as a concession to environmental critics of genetic
engineering. Even though those first promoting refuge were rabid
biotechnology advocates the approach was taken up by environmental critics
who seem unaware of the potential disaster associated with the appearance
of dominant Bt mutants. My repeated warning about the potential danger fell
on deaf ears.
Bureaucrats such as those in Biotechnology Canada are highly paid but not
strong in genetics or for that matter in most substantial scientific
matters. They are very slow to act to reverse a poor policy and quick to
place blame when policy fails.
My expectation is that if the dominant mutants spread rapidly promoted by
refuge the bureaucrats will place blame on environmental critics and use
that blame to promote even more destructive biotechnology.
I hope that some others will recognize that dominant Bt mutants spell
disaster and urge moratorium on the spread Bt crops until the problem of
resistance can be dealt with in a scientific way, on recognizing the
reality of dominant mutations.
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