Mutation could make organic pesticide useless

Aozotorp at Aozotorp at
Mon Aug 6 12:12:42 EDT 2001

Mutation could make organic pesticide useless
By Steve Connor Science Editor
06 August 2001
Scientists have found the Achilles' heel of the world's most popular organic 
pesticide. The findings could fatally undermine its role as a safe form of 
insect control in the developing world.

The pesticide is favoured by organic farmers not just because of its 
effectiveness but also because it is composed of toxins produced naturally by 
microbes in the soil. However, researchers have identified a gene that makes 
insects resistant to the toxins, rendering the pesticide useless.

For decades, organic farmers have sprayed their crops with Bacillus 
thuringiensis (Bt), a bacterium that produces toxins poisonous to insects and 
pests but harmless to other animals and humans.

In more recent years, biotechnologists have inserted key genes from the Bt 
microbe directly into genetically modified crops to give them an inbuilt 
resistance to pests.

However, it was feared that this strategy could backfire because the more 
crops that are grown with Bt genes, the more likely it is that resistance 
would develop. Now, scientists believe this fear is justified, after 
discovering a genetic mutation of a moth that attacks cotton plants, one of 
the crops that have been genetically modified with Bt genes.

The international team of researchers, led by Fred Gould, professor of 
entomology at North Carolina State University, said moths carrying two copies 
of the gene were highly resistant to Bt toxins.

The researchers estimate that 0.15 per cent of moths in the wild currently 
carry the resistance gene. But it could take just 10 years for this 
percentage to increase to a point where it would pose a serious problem to 

Professor Gould said: "Not only will knowledge about this gene enable us to 
detect the early signs of pests evolving resistance to the current engineered 
plants, it may also allow us to modify plants so they will be defended 
against the new pest strains."

A separate group of scientists from the University of California at San Diego 
have found that Bt resistance is also present in microscopic roundworms, such 
as nematodes, which also pose a serious threat to crops.

Raffi Aroian, professor of biology at the university, said: There are insects 
in the wild now with gene variants that allow them to be resistant to Bt 

"As more crops with Bt genes are planted, it is only a matter of time before 
populations of Bt-resistant insects grow numerous enough to become 
economically troublesome to farmers hoping to control them."

Professor Aroian's team found that a single mutation in a gene that disables 
an enzyme in the insect pest's gut is responsible for imparting resistance to 
a range of Bt toxins.

"For people using Bt toxins to control insects, this is a particularly 
threatening scenario," Professor Aroian said. It means that resistance to a 
range of pesticides based on Bt toxins can come about "with one swoop", he 

"Even if Bt toxins weren't used to fight insects, nematodes are an enormous 

"At the last estimate, which was 13 years ago, they caused $80bn (£56bn) 
worth of crop damage a year." 

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