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2-Plants: Corn refuge spreads dominant Bt mutants

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TITLE:  Corn refuge spreads dominant Bt mutants
SOURCE: Prof. Joe Cummins,
DATE:   May 6, 1999

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Corn refuge spreads dominant Bt mutants

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 irefugei 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 re!
fuge 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 destructi!
ve 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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