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GM Crop Use Makes Minor Pests Major Problem
GM Crop Use Makes Minor Pests Major Problem
Tuesday, April 20, 2010 Author: Jane Qiu Source: Nature News
Pesticide use rising as Chinese farmers fight insects thriving on transgenic crop.
Growing cotton that has been genetically modified to poison its main pest can lead
to a boom in the numbers of other insects, a ten-year study in northern China has
found.
In 1997, the Chinese government approved the commercial cultivation of cotton
plants genetically modified to produce a toxin from the bacteria Bacillus thuringiensis
(Bt) that is deadly to the bollworm Helicoverpa armigera. Outbreaks of larvae of the
cotton bollworm moth in the early 1990s had hit crop yields and profits, and the
pesticides used to control the bollworm damaged the environment and caused
thousands of deaths from poisoning each year
More than 4 million hectares of Bt cotton are now grown in China. Since the crop
was approved, a team led by Kongming Wu, an entomologist at the Chinese
Academy of Agricultural Sciences in Beijing, has monitored pest populations at 38
locations in northern China, covering 3 million hectares of cotton and 26 million
hectares of various other crops.
Numbers of mirid bugs (insects of the Miridae family), previously only minor pests in
northern China, have increased 12-fold since 1997, they found. "Mirids are now a
main pest in the region," says Wu. "Their rise in abundance is associated with the
scale of Bt cotton cultivation."
Wu and his colleagues suspect that mirid populations increased because less broad-
spectrum pesticide was used following the introduction of Bt cotton. "Mirids are not
susceptible to the Bt toxin, so they started to thrive when farmers used less
pesticide," says Wu. The study is published in this week's issue of Science1.
"Mirids can reduce cotton yields just as much as bollworms, up to 50% when not
controlled," Wu adds. The insects are also emerging as a threat to crops such as
green beans, cereals, vegetables and various fruits.
Rise of the mirids
The rise of mirids has driven Chinese farmers back to pesticides — they are
currently using about two-thirds as much as they did before Bt cotton was
introduced. As mirids develop resistance to the pesticides, Wu expects that farmers
will soon spray as much as they ever did.
Two years ago, a study led by David Just, an economist at Cornell University at
Ithaca, New York, concluded that the economic benefits of Bt cotton in China have
eroded2. The team attributed this to increased pesticide use to deal with secondary
pests.
The conclusion was controversial, with critics of the study focusing on the relatively
small sample size and use of economic modelling. Wu's findings back up the earlier
study, says David Andow, an entomologist at the University of Minnesota in St Paul.
"The finding reminds us yet again that genetic modified crops are not a magic bullet
for pest control," says Andow. "They have to be part of an integrated pest-
management system to retain long-term benefits."
From the ashes
Whenever a primary pest is targeted, other species are likely to rise in its place. For
example, the boll weevil was once the main worldwide threat to cotton. As farmers
sprayed pesticides against the weevils, bollworms developed resistance and rose to
become the primary pest. Similarly, stink bugs have replaced bollworms as the
primary pest in southeastern United States since Bt cotton was introduced.
Along with genetically modified crops, says Andow, farmers need effective systems
for responding to changes in pest abundance. This needs to be based on research
into the timing, dosage and frequency of pesticide use needed to tackle new pests.
"When farmers decide how to control pests, they tend to overuse pesticides," he
says.
Wu and his colleagues are seeking the most effective way to use pesticide, and
trying to reduce mirid damage to cotton by growing crops the pests prefer nearby.
Meanwhile, Chinese researchers are trying to develop cotton plants that kill both
bollworms and mirids.
Wu stresses, however, that pest control must keep sight of the whole ecosystem.
"The impact of genetically modified crops must be assessed on the landscape level,
taking into account the ecological input of different organisms," he says. "This is the
only way to ensure the sustainability of their application."
References
1.Lu, Y. et al. Science advance online publication doi:10.1126/science.1187881
(2010).
2.Wang, S., Just, D. & Pinstrup-Anderson, P. Int. J. Biotechnol. 10, 113-120 (2008). |
Article
Tuesday, April 20, 2010 Author: Jane Qiu Source: Nature News
Pesticide use rising as Chinese farmers fight insects thriving on transgenic crop.
Growing cotton that has been genetically modified to poison its main pest can lead
to a boom in the numbers of other insects, a ten-year study in northern China has
found.
In 1997, the Chinese government approved the commercial cultivation of cotton
plants genetically modified to produce a toxin from the bacteria Bacillus thuringiensis
(Bt) that is deadly to the bollworm Helicoverpa armigera. Outbreaks of larvae of the
cotton bollworm moth in the early 1990s had hit crop yields and profits, and the
pesticides used to control the bollworm damaged the environment and caused
thousands of deaths from poisoning each year
More than 4 million hectares of Bt cotton are now grown in China. Since the crop
was approved, a team led by Kongming Wu, an entomologist at the Chinese
Academy of Agricultural Sciences in Beijing, has monitored pest populations at 38
locations in northern China, covering 3 million hectares of cotton and 26 million
hectares of various other crops.
Numbers of mirid bugs (insects of the Miridae family), previously only minor pests in
northern China, have increased 12-fold since 1997, they found. "Mirids are now a
main pest in the region," says Wu. "Their rise in abundance is associated with the
scale of Bt cotton cultivation."
Wu and his colleagues suspect that mirid populations increased because less broad-
spectrum pesticide was used following the introduction of Bt cotton. "Mirids are not
susceptible to the Bt toxin, so they started to thrive when farmers used less
pesticide," says Wu. The study is published in this week's issue of Science1.
"Mirids can reduce cotton yields just as much as bollworms, up to 50% when not
controlled," Wu adds. The insects are also emerging as a threat to crops such as
green beans, cereals, vegetables and various fruits.
Rise of the mirids
The rise of mirids has driven Chinese farmers back to pesticides — they are
currently using about two-thirds as much as they did before Bt cotton was
introduced. As mirids develop resistance to the pesticides, Wu expects that farmers
will soon spray as much as they ever did.
Two years ago, a study led by David Just, an economist at Cornell University at
Ithaca, New York, concluded that the economic benefits of Bt cotton in China have
eroded2. The team attributed this to increased pesticide use to deal with secondary
pests.
The conclusion was controversial, with critics of the study focusing on the relatively
small sample size and use of economic modelling. Wu's findings back up the earlier
study, says David Andow, an entomologist at the University of Minnesota in St Paul.
"The finding reminds us yet again that genetic modified crops are not a magic bullet
for pest control," says Andow. "They have to be part of an integrated pest-
management system to retain long-term benefits."
From the ashes
Whenever a primary pest is targeted, other species are likely to rise in its place. For
example, the boll weevil was once the main worldwide threat to cotton. As farmers
sprayed pesticides against the weevils, bollworms developed resistance and rose to
become the primary pest. Similarly, stink bugs have replaced bollworms as the
primary pest in southeastern United States since Bt cotton was introduced.
Along with genetically modified crops, says Andow, farmers need effective systems
for responding to changes in pest abundance. This needs to be based on research
into the timing, dosage and frequency of pesticide use needed to tackle new pests.
"When farmers decide how to control pests, they tend to overuse pesticides," he
says.
Wu and his colleagues are seeking the most effective way to use pesticide, and
trying to reduce mirid damage to cotton by growing crops the pests prefer nearby.
Meanwhile, Chinese researchers are trying to develop cotton plants that kill both
bollworms and mirids.
Wu stresses, however, that pest control must keep sight of the whole ecosystem.
"The impact of genetically modified crops must be assessed on the landscape level,
taking into account the ecological input of different organisms," he says. "This is the
only way to ensure the sustainability of their application."
References
1.Lu, Y. et al. Science advance online publication doi:10.1126/science.1187881
(2010).
2.Wang, S., Just, D. & Pinstrup-Anderson, P. Int. J. Biotechnol. 10, 113-120 (2008). |
Article