GENET archive

[Index][Thread]

RISK ASSESSMENT & TECHNOLOGY: U.S. researchers identify how insects resist Bt pesticides



                                  PART 1


------------------------------- GENET-news -------------------------------

TITLE:   RESEARCHERS IDENTIFY HOW INSECTS RESIST BT PESTICIDES

SOURCE:  Cornell University, USA

AUTHOR:  Cornell Chronicle, by Krishna Ramanujan

URL:     http://www.news.cornell.edu/stories/Aug11/BtLooper.html

DATE:    29.08.2011

SUMMARY: "Under normal circumstances, the Bt toxin Cry1Ac, which is a caterpillar-specific toxin, binds to an enzyme called APN 1 along the wall of the insect?s gut, where the toxin destroys the gut lining. But when cabbage loopers develop resistance, APN 1 significantly decreases while another aminopeptidase, APN 6, which does not bind to Bt, significantly increases, allowing the insect to properly digest food and Bt without harm."

----- archive: http://www.genet-info.org/information-services.html -----


RESEARCHERS IDENTIFY HOW INSECTS RESIST BT PESTICIDES

For the first time, researchers have identified how cabbage looper caterpillars in the field develop resistance to the bacterium Bacillus thuringiensis (Bt), which naturally occurs in the soil and on plants and has been developed into the most successful and widely used biological insecticide.

When ingested, the insecticidal toxins in Bt kill insects by destroying their guts. Insects in the field develop resistance to it, however, via a genetic mechanism that alters a toxin receptor in the insect?s gut, two Cornell researchers have discovered. The receptor belongs to a class of digestive enzymes called aminopeptidase N (APN), two of which undergo changes when cabbage loopers develop resistance to Bt on crops.

Under normal circumstances, the Bt toxin Cry1Ac, which is a caterpillar-specific toxin, binds to an enzyme called APN 1 along the wall of the insect?s gut, where the toxin destroys the gut lining. But when cabbage loopers develop resistance, APN 1 significantly decreases while another aminopeptidase, APN 6, which does not bind to Bt, significantly increases, allowing the insect to properly digest food and Bt without harm.

?If an insect loses an aminopeptidase N, you will expect to see an negative effect on the physiology of the insect gut,? said Ping Wang, associate professor of entomology and senior author of the paper published online in the Aug. 15 issue of the Proceedings of the National Academy of Sciences. Kasorn Tiewsiri, a postdoctoral associate in Wang?s lab, is the paper?s lead author.

?To compensate for the loss of the enzyme APN 1, the activity of APN 6 jumps up high, and that allows the insect to perform a normal digestive process, where Bt no longer binds to the gut,? Wang added.

Organic farmers use Bt as a key weapon against insects, and crops genetically engineered with insecticidal Bt genes are now sown on 59 million hectares (more than 145 million acres) worldwide.

Farmers first reported Bt resistance in the field 20 years ago. Since then, researchers have uncovered a number of mechanisms for resistance in insects in the lab, but then learned that lab insects, which don?t face the same stressors as field insects, develop different tactics for overcoming Bt.

In this study, Wang and Tiewsiri obtained cabbage loopers from greenhouses in British Columbia that were resistant to Bt and crossed them with a lab strain that had no resistance. The progeny carried the isolated Bt-resistant trait from their field-stressed parent. The researchers then used that line of cabbage loopers to conduct biochemical, proteomic and molecular studies.

Next, the researchers plan on trying to identify which gene mutates in the Bt-resistant insects, how that gene controls the expression of targeted proteins, and uncover resistance mechanisms to other Bt toxins, as many varieties are used in agriculture. The researchers hope their studies will lead to new management strategies for Bt-resistant insects, Wang said.

The study was funded by the U.S. Department of Agriculture?s National Institute of Food and Agriculture.



                                  PART 2

------------------------------- GENET-news -------------------------------

TITLE:   REACHING INDIAN FARMERS ON PINK BOLLWORM RESISTANCE

SOURCE:  Monsanto, USA

AUTHOR:  Monsanto Blog, by Sara Duncan

URL:     http://www.monsantoblog.com/2011/08/23/reaching-indian-farmers-on-pink-bollworm-resistance/?utm_source=rss&utm_medium=rss&utm_campaign=reaching-indian-farmers-on-pink-bollworm-resistance

DATE:    23.08.2011

SUMMARY: "In 2010, resistance to pink bollworm was detected in five districts of Gujarat state, threatening the crops of more than five million farmers who planted Bollgard and Bollgard II cotton in India. [...] A global team of Monsanto experts stepped up to create and advocate a nationwide campaign on the importance of resistance management for preserving the long-term value of insect-control traits in cotton"

----- archive: http://www.genet-info.org/information-services.html -----


REACHING INDIAN FARMERS ON PINK BOLLWORM RESISTANCE

Mention of the words ?insect resistance? can cause panic; particularly among farmers growing a crop that can be devastated by the insects developing resistance. To farmers, insect resistance means the technology that prevents them from having to spray round-after-round of insecticide is in jeopardy. To farmers who rely on selling that crop to feed their families, resistance endangers their livelihoods.

In 2010, resistance to pink bollworm was detected in five districts of Gujarat state, threatening the crops of more than five million farmers who planted Bollgard® and Bollgard II® cotton in India. The detection also meant concerns could heighten about the technology and possibly halt the advancement of similar technology in India; technology that could provide added benefits to farmers growing cotton in India.

A global team of Monsanto experts stepped up to create and advocate a nationwide campaign on the importance of resistance management for preserving the long-term value of insect-control traits in cotton. The team engaged stakeholders and media through an open discussion about resistance data.

The team also organized more than 55 stakeholder meetings, two workshops, and six seminars in a span of six months. The team educated farmers about the existence of resistance in pink bollworm to Bollgard and briefed Monsanto?s technology partners about related resistance issues. This enabled the partners to make informed decisions about seed production and what to plant next season. The team also reiterated to the scientific community the importance of refuge in sustaining insect-control trait technology and highlighted Monsanto?s global policy of making public declarations regarding resistance development in pests.

?The most challenging aspect of this project was that Monsanto?s intention was to be transparent with the findings on resistance in pink bollworm populations in Gujarat state, but the message was misconstrued by regulators as a marketing ploy to promote Bollgard II,? Leigh English, director of the Monsanto research center in Bangalore, India, said. ?Despite these challenges, the team continued to communicate to all the stakeholders and media through open discussion. This was followed by face-to-face meetings, workshops, seminars and a nationwide awareness campaign.?

The methodology adopted, data obtained and the team?s interpretation of resistance was shared with concerned stakeholders with complete transparency. The team also partnered with the Central Institute for Cotton Research to conduct a joint resistance monitoring program in pink bollworm populations during the 2010 growing season. Team members have also conducted a workshop aimed at adopting a uniform methodology for resistance monitoring.

?This approach is highly applicable in all geographies in handling detection and management of insect resistance for insect-protected trait crops; thereby sustaining customer value,? English said. ?The technology partners and the Indian regulators, through this incidence, have realized the importance of planting refuge, thus calling for joint meetings and deliberations to develop insect-resistance management strategies.?



                                  PART 3

------------------------------- GENET-news -------------------------------

TITLE:   COTTON ?TOPPING? CUTS BOLLWORM INFESTATIONS, STUDY FINDS

SOURCE:  SciDev.Net, UK

AUTHOR:  Bernard Appiah

URL:     http://www.scidev.net/en/news/cotton-topping-cuts-bollworm-infestations-study-finds.html

DATE:    02.08.2011

SUMMARY: "Cutting the shoot tips of the tops of cotton plants may control key pests and potentially reduce cotton farmers? dependence on insecticides, according to a study by researchers from Mali. The researchers say the practice - called topping - is already known to improve yields but the effect on pests in Sub-Saharan Africa have not been previously studied."

----- archive: http://www.genet-info.org/information-services.html -----


COTTON ?TOPPING? CUTS BOLLWORM INFESTATIONS, STUDY FINDS

Cutting the shoot tips of the tops of cotton plants may control key pests and potentially reduce cotton farmers? dependence on insecticides, according to a study by researchers from Mali.

The researchers say the practice - called topping - is already known to improve yields but the effect on pests in Sub-Saharan Africa have not been previously studied.

Cotton is mainly grown by poor small-scale farmers in Sub-Saharan Africa, where millions depend on it for their livelihood, according to researchers.

A combination of the high cost of insecticides and emerging pest resistance have motivated researchers to look at topping - which had been shown to reduce pest levels in a handful of studies in China, Egypt, and India - to examine its potential for pest control in Africa.

They therefore looked at infestation levels of three bollworm species, cotton?s main pests in Sub-Saharan Africa, which account for significant seed cotton yield losses, in topped versus non-topped fields.

The researchers conducted 12 trials comparing manual topping and non-topping cotton plots in Mali over a six-year period beginning in 2002.

The results, published online in Crop Protection last month (2 July), showed that bollworm infestations were always lower on topped cotton and seven out of 12 trials had significantly lowered infestations on topped cotton.

Researchers recorded an average of 56 per cent fewer H. armigera larvae, 68 per cent fewer Earias spp. larvae, and 71 per cent fewer D. watersi, and the reduction in infestation was the greatest in years when the pests were the most numerous.

?We were amazed to see that non-topped cotton plants in plots near the topped plants also had reduced bollworm infestations,? said Mamoutou Togola, co-author of the research and an entomologist at Mali?s Institute of Rural Economy.

They did not investigate why topping reduces pest numbers, or whether it could save money by significantly reducing insecticide use - both topics left for future research.

But, according to Togola, topping may be relevant to African countries whose economies largely depend on cotton, such as Benin, Burkina Faso, Chad and Mali where about 10 million people depend on cotton farming.

Rafiq Chaudhry, head of technical information at the International Cotton Advisory Committee, in United States, said many cotton-producing countries, such as Argentina, India and Pakistan, do not employ topping, although it ?may control some pests?.

?We always recommend that insecticides be used minimally and other non-chemical control practices be encouraged,? Chaudhry said.

Ibrahim Sourabié, the country coordinator of the West African Cotton Improvement Program in Burkina Faso, said that cotton farmers there use genetically modified Bt cotton or oil extracted from the seeds of neem tree to control pests. But, he added, topping could help conventional cotton farmers control bollworm infestations.

Link to article abstract in Crop Protection

http://www.sciencedirect.com/science/article/pii/S0261219411001980



                                  PART 4

------------------------------- GENET-news -------------------------------

TITLE:   RAPID EVOLUTION WITHIN SINGLE CROP-GROWING CEASON INCREASES INSECT PEST NUMBERS

SOURCE:  University of California - Riverside, USA

AUTHOR:  Press Release

URL:     http://newsroom.ucr.edu/2702

DATE:    15.08.2011

SUMMARY: "New research [...] shows that evolution ? genetic changes in populations over time ? can occur so rapidly in organisms that its impact on population numbers and other aspects of biology can be seen within just a few generations. [...] ?This shows that even without human interference natural selection acting on aphid populations causes rapid evolution,? said Martin M. Turcotte, who led the research as a graduate student in ecology, evolution and organismal biology at UC Riverside. ?Even stronger effects might be expected when pesticides are in use."

----- archive: http://www.genet-info.org/information-services.html -----


RAPID EVOLUTION WITHIN SINGLE CROP-GROWING CEASON INCREASES INSECT PEST NUMBERS

RIVERSIDE, Calif. ? New research by scientists at the University of California, Riverside shows that evolution ? genetic changes in populations over time ? can occur so rapidly in organisms that its impact on population numbers and other aspects of biology can be seen within just a few generations.

The research, published online Aug. 9 in Ecology Letters, the highest ranked journal in the field of ecology, can improve scientists? ability to predict the growth and spread of endangered species, invasive species, and disease epidemics.

Working on aphids, considered the world?s most important crop pest, the researchers experimentally tested the impact of rapid evolution on wild populations within a single crop-growing season. To accomplish this, the researchers set up an experiment that prevented evolution by natural selection from occurring in some aphids while allowing it in others. They then compared the rate at which the non-evolving and evolving populations grew.

Each fall, aphids undergo one generation of sexual reproduction. The following spring, they begin multiple generations of asexual reproduction. During this period multiple clonal lineages compete, leading to changes in gene frequencies and mean trait values in the population in the process.

In their field experiment, the researchers compared replicated aphid populations that were non-evolving (single clone, thus genetically identical) to aphid populations that were potentially evolving (two clones genetically different from each other and with dissimilar growth rates).

As the populations grew, the researchers tested whether the mixed populations evolved. Counting aphids repeatedly, they found that clones rapidly changed in frequency, within 30 days or 4-5 aphid generations. They then tested the impact of this evolutionary change on the ecology of the aphids. They found that evolving populations grew in number up to 42 percent faster than non-evolving populations.

?This shows that even without human interference natural selection acting on aphid populations causes rapid evolution,? said Martin M. Turcotte, who led the research as a graduate student in ecology, evolution and organismal biology at UC Riverside. ?Even stronger effects might be expected when pesticides are in use. For decades, evolution was deemed too slow and, hence, it was not considered when studying population growth ? an oversight that needs to be corrected. Ignoring this evolution, as is not currently uncommon, can lead to predictions that greatly underestimate pest densities and outbreaks.?

Rapid evolution could have important untested impacts in many other applied areas. For example, rapid evolution is important in fisheries where intense fishing causes fish to evolve traits that let them escape fishing nets. Antibiotic resistance and increased virulence in pathogens are examples where rapid evolution impacts human health.

The study was conducted at the University of California Motte Rimrock Reserve where the researchers collected multiple clonal lineages from a wild aphid population feeding on mustard plants. They identified clones and characterized their intrinsic per capita growth rates in a greenhouse at UCR.

Turcotte graduated with a doctoral degree in biology from UCR this year. Currently a postdoctoral scholar at the University of Toronto at Mississauga, Canada, he uses experimental evolution to study fundamental questions about the ecology and evolution of plant-herbivore interactions.

He was joined in the research by his co-advisors at UCR: David N. Reznick, a professor of biology, and J. Daniel Hare, a professor of entomology. A few UCR biology undergraduate students also assisted the research team.

Turcotte was funded by grants from the Natural Sciences and Engineering Research Council of Canada; Fonds de Recherche du Québec and the University of California Natural Reserve System. Grants from the U.S. National Science Foundation supported Reznick and Hare in the study.