Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Trouble on the Horizon for GM Crops?

20.06.2012
Pests are adapting to genetically modified crops in unexpected ways, researchers have discovered. The findings underscore the importance of closely monitoring and countering pest resistance to biotech crops.

Resistance of cotton bollworm to insect-killing cotton plants involves more diverse genetic changes than expected, an international research team reports in the journal Proceedings of the National Academy of Sciences.

To decrease sprays of broad-spectrum insecticides, which can harm animals other than the target pests, cotton and corn have been genetically engineered to produce toxins derived from the bacterium Bacillus thuringiensis, or Bt.

Bt toxins kill certain insect pests but are harmless to most other creatures including people. These environmentally friendly toxins have been used for decades in sprays by organic growers and since 1996 in engineered Bt crops by mainstream farmers.

Over time, scientists have learned, initially rare genetic mutations that confer resistance to Bt toxins are becoming more common as a growing number of pest populations adapt to Bt crops.

In the first study to compare how pests evolve resistance to Bt crops in the laboratory vs. the field, researchers discovered that while some the of the lab-selected mutations do occur in the wild populations, some mutations that differ markedly from those seen in the lab are important in the field.

Caterpillars of the cotton bollworm, Helicoverpa armigera, can munch on a wide array of plants before emerging as moths. This species is the major cotton pest in China, where the study was carried out.

Bruce Tabashnik, head of the department of entomology at the University of Arizona College of Agriculture and Life Sciences, who co-authored the study, considers the findings an early warning to farmers, regulatory agencies and the biotech industry.

"Scientists expected the insects to adapt, but we're just finding out now how they're becoming resistant in the field," Tabashnik said.

To avoid surprises, researchers have exposed cotton bollworm populations to Bt toxins in controlled lab experiments and studied the genetic mechanisms by which the insects adapt.

"We try to stay ahead of the game," he said. "We want to anticipate what genes are involved, so we can proactively develop strategies to sustain the efficacy of Bt crops and reduce reliance on insecticide sprays. The implicit assumption is what we learn from lab-selected resistance will apply in the field."

That assumption, according to Tabashnik, had never been tested before for resistance to Bt crops.

Now for the first time, the international team gathered genetic evidence from pests in the field, enabling them to directly compare the genes involved in the resistance of wild and lab-reared populations.

They found some resistance-conferring mutations in the field were the same as in lab-reared pests, but some others were strikingly different.

"We found exactly the same mutation in the field that was detected in the lab," Tabashnik said. "But we also found lots of other mutations, most of them in the same gene and one in a completely different gene."

A major surprise came when the team identified two unrelated, dominant mutations in the field populations. "Dominant" means that one copy of the genetic variant is enough to confer resistance to Bt toxin. In contrast, resistance mutations characterized before from lab selection are recessive ­ meaning it takes two copies of the mutation, one provided by each parent, to make an insect resistant to Bt toxin.

"Dominant resistance is more difficult to manage and cannot be readily slowed with refuges, which are especially useful when resistance is recessive," Tabashnik said.

Refuges consist of plants that do not have a Bt toxin gene and thus allow survival of insects that are susceptible to the toxin. Refuges are planted near Bt crops with the goal of producing enough susceptible insects to dilute the population of resistant insects, by making it unlikely two resistant insects will mate and produce resistant offspring.

According to Tabashnik, the refuge strategy worked brilliantly against the pink bollworm in Arizona, where this pest had plagued cotton farmers for a century, but is now scarce.

The dominant mutations discovered in China throw a wrench in the refuge strategy because resistant offspring arise from matings between susceptible and resistant insects.

He added that the study will enable regulators and growers to better manage emerging resistance to Bt crops.

"We have been speculating and using indirect methods to try and predict what would happen in the field. Only now that resistance is starting to pop up in many places is it possible to actually examine resistance in the field. I think the techniques from this study will be applied to many other situations around the world, and we'll begin to develop a general understanding of the genetic basis of resistance in the field."

The current study is part of a collaboration funded by the Chinese government, involving a dozen scientists at four institutions in China and the U.S. Yidong Wu at Nanjing Agricultural University designed the study and led the Chinese effort. He emphasized the importance of the ongoing collaboration for addressing resistance to Bt crops, which is a major issue in China. He also pointed out that the discovery of dominant resistance will encourage the scientific community to rethink the refuge strategy.

Tabashnik said China is the world's top cotton producer, with about 16 billion pounds of cotton per year. India is number two, followed by the U.S., which produces about half as much cotton as China.

In 2011, farmers worldwide planted 160 million acres of Bt cotton and Bt corn. The percentage of cotton planted with Bt cotton reached 75 per cent in the U.S. in 2011, but has exceeded 90 per cent since 2004 in northern China, where most of China's cotton is grown.

The researchers report that resistance-conferring mutations in cotton bollworm were three times more common in northern China than in areas of northwestern China where less Bt cotton has been grown.

Even in northern China, however, growers haven't noticed the emerging resistance yet, Tabashnik said, because only about 2 percent of the cotton bollworms there are resistant.

"As a grower, if you're killing 98 percent of pests with Bt cotton, you wouldn't notice anything. But this study tells us there is trouble on the horizon."

LINKS:
Reference:
Haonan Zhang et al., Diverse genetic basis of field-evolved resistance to Bt cotton in cotton bollworm from China, PNAS June 11, 2012 http://www.pnas.org/content/early/2012/06/06/1200156109.abstract
University of Arizona Department of Entomology:
http://ag.arizona.edu/ento/index.htm
Nanjing Agricultural University, China: http://english.njau.edu.cn
CONTACTS:
Bruce Tabashnik
College of Agriculture and Life Sciences
520-621-1141
brucet@cals.arizona.edu
Daniel Stolte
University Communications
520-626-4402
stolte@email.arizona.edu

Daniel Stolte | University of Arizona
Further information:
http://www.arizona.edu

More articles from Agricultural and Forestry Science:

nachricht Plasma-zapping process could yield trans fat-free soybean oil product
02.12.2016 | Purdue University

nachricht New findings about the deformed wing virus, a major factor in honey bee colony mortality
11.11.2016 | Veterinärmedizinische Universität Wien

All articles from Agricultural and Forestry Science >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Electron highway inside crystal

Physicists of the University of Würzburg have made an astonishing discovery in a specific type of topological insulators. The effect is due to the structure of the materials used. The researchers have now published their work in the journal Science.

Topological insulators are currently the hot topic in physics according to the newspaper Neue Zürcher Zeitung. Only a few weeks ago, their importance was...

Im Focus: Significantly more productivity in USP lasers

In recent years, lasers with ultrashort pulses (USP) down to the femtosecond range have become established on an industrial scale. They could advance some applications with the much-lauded “cold ablation” – if that meant they would then achieve more throughput. A new generation of process engineering that will address this issue in particular will be discussed at the “4th UKP Workshop – Ultrafast Laser Technology” in April 2017.

Even back in the 1990s, scientists were comparing materials processing with nanosecond, picosecond and femtosesecond pulses. The result was surprising:...

Im Focus: Shape matters when light meets atom

Mapping the interaction of a single atom with a single photon may inform design of quantum devices

Have you ever wondered how you see the world? Vision is about photons of light, which are packets of energy, interacting with the atoms or molecules in what...

Im Focus: Novel silicon etching technique crafts 3-D gradient refractive index micro-optics

A multi-institutional research collaboration has created a novel approach for fabricating three-dimensional micro-optics through the shape-defined formation of porous silicon (PSi), with broad impacts in integrated optoelectronics, imaging, and photovoltaics.

Working with colleagues at Stanford and The Dow Chemical Company, researchers at the University of Illinois at Urbana-Champaign fabricated 3-D birefringent...

Im Focus: Quantum Particles Form Droplets

In experiments with magnetic atoms conducted at extremely low temperatures, scientists have demonstrated a unique phase of matter: The atoms form a new type of quantum liquid or quantum droplet state. These so called quantum droplets may preserve their form in absence of external confinement because of quantum effects. The joint team of experimental physicists from Innsbruck and theoretical physicists from Hannover report on their findings in the journal Physical Review X.

“Our Quantum droplets are in the gas phase but they still drop like a rock,” explains experimental physicist Francesca Ferlaino when talking about the...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ICTM Conference 2017: Production technology for turbomachine manufacturing of the future

16.11.2016 | Event News

Innovation Day Laser Technology – Laser Additive Manufacturing

01.11.2016 | Event News

#IC2S2: When Social Science meets Computer Science - GESIS will host the IC2S2 conference 2017

14.10.2016 | Event News

 
Latest News

Researchers identify potentially druggable mutant p53 proteins that promote cancer growth

09.12.2016 | Life Sciences

Scientists produce a new roadmap for guiding development & conservation in the Amazon

09.12.2016 | Ecology, The Environment and Conservation

Satellites, airport visibility readings shed light on troops' exposure to air pollution

09.12.2016 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>