[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[SANET-MG] bollworm pests beaten
I wonder whether or not the comments below about the long term
resistance to pink bollworm caused those making the comments to laugh
behind their hands.The most important factor in the absence of
resistance was not mentioned in the article. That factor is the fact
that USDA allows cotton farmers to spray the refuges with chemical
insecticides to kill off any resistant insects.
Published online: 10 October 2005; | doi:10.1038/news051010-5
Bollworm pest remains beaten
Genetic study confirms insects are still not resistant to Bt toxin.
Cotton modified to repel pests is still going strong - and the pests are
still kept away.
Cotton that has been genetically engineered to be toxic to pests remains
effective after nearly a decade in the field, scientists have announced,
defying predictions that insects would evolve to tolerate them.
Widespread planting of genetically modified (GM) cotton across the
southern United States has not increased the incidence of resistance in
the major insect pest, pink bollworm.
Cotton varieties genetically modified to produce a natural insecticide,
the Bt toxin, borrowed from the bacterium Bacillus thuringiensis, have
been planted commercially in the United States since 1996. Many experts
predicted that pests would evolve to resist the toxin within a few years.
But research published in Proceedings of the National Academy of
Sciences today shows that this has not yet happened1. A survey of pink
bollworm in Arizona, where Bt cotton makes up more than half of the
cotton grown, shows that genes for Bt resistance have not become more
common since 1997.
"Ten years ago many experts were predicting resistance within three
years," says Bruce Tabashnik, lead author of the new research, which was
partially funded by the company Monsanto. "If I had made a prediction, I
would have said it would be maybe four to eight years until resistance
evolved." Tabashnik and colleagues were surprised in 2003 when they
found little evidence of resistance in pests2 (see 'Resistance to Bt
toxin surprisingly absent from pests'). Two years on, their genetic
study confirms those earlier results.
But there is no question of Bt cotton being indefinitely effective,
Tabashnik adds. "I would say we might see resistance in maybe five
additional years," he says.
The researchers used a mathematical model in an attempt to explain how
and why the insects have not developed resistance.
Farming practices are one reason, they conclude. The US Department of
Agriculture requires that farmers growing Bt cotton plant at least 5% of
their crop interspersed with 'refuge' zones of non-Bt cotton. Mixing of
insects from within the refuges, which do not gain an advantage from the
resistance genes, with insects from the GM crops, is intended to dilute
the concentration of resistance genes. The latest research shows that
this strategy seems to work.
But there are additional factors at play. Bt-resistant insects do not
survive as well in refuges as non-resistant ones, the researchers note.
And the genes for resistance are recessive, so that only insects
carrying two copies have the trait.
Not over yet
Despite the findings, researchers continue to be concerned that
resistance will one day be a problem. "Compared to conventional
insecticides, Bt crops have done extremely well, but it's inevitable
that resistance will evolve," says Graham Moores, a senior research
biochemist at Rothamsted Research in Harpenden, UK.
Moores recently contributed to work that found a novel kind of Bt
resistance in cotton bollworm bugs from GM fields in Australia3. If
these insects have a different kind of resistance mechanism, then others
could too, he says; so there could be genes for resistance out there
that behave differently from the one studied in Arizona.
"The existing management strategies have been successful, but we cannot
rest on our laurels," says Moores. Bt cotton is grown on a large scale
in China, South Africa and Australia.
One hope that the evolution of pests resistant to Bt cotton can be
delayed further lies with the second generation of the GM crop. These
plants carry another bacterial gene and so produce two Bt toxins. In
Australia, the government allows only this variety to be grown, and it
is also becoming more popular in the United States. These crops are
safer because it is less likely that pests could evolve to be resistant
to both toxins. "Two-toxin cotton should last longer, at the very least
twice as long, and it could be much more," says Tabashnik.
Tabashnik B.E., et al. Proceedings of the National Academy of Sciences
of the United States of America http://www.pnas.org/cgi/doi/
CarriÃ¨re Y., et al. Proceedings of the National Academy of Sciences of
the United States of America, 100. 1519 - 1523
Gunning R.V., et al. Applied and Environmental Microbiology, 71. 2558 -
2563 doi:10.1128/AEM.71.5.2558-2563.2005 (2005). | Article | PubMed |
ISI | ChemPort |
Story from firstname.lastname@example.org:
To unsubscribe from SANET-MG:
1- Visit http://lists.sare.org/archives/sanet-mg.html to unsubscribe or;
2- Send a message to <email@example.com> from the address subscribed to the list. Type "unsubscribe sanet-mg" in the body of the message.
Visit the SANET-MG archives at: http://lists.sare.org/archives/sanet-mg.html
For more information on grants and other resources available through the SARE program, please visit http://www.sare.org.