Corn and cotton have been modified genetically to produce pest-killing proteins from the bacterium Bacillus thuringiensis or Bt for short.
Compared with typical insecticide sprays the Bt toxins produced by genetically engineered crops are much safer for people
Although Bt crops have helped to reduce insecticide sprays boost crop yields and increase farmer profits their benefits will be short-lived
Bt crops were grown first widely in 1996 and several pests have already become resistant to plants that produce a single Bt toxin.
To thwart further evolution of pest resistance to Bt crops farmers have shifted recently to the pyramid strategy:
As reported in the study the pyramid strategy has been adopted extensively with two-toxin Bt cotton completely replacing one-toxin Bt cotton
His home institution the Center for Agricultural Research for Development or CIRAD is interested keenly in factors that could affect pest resistance to Bt crops in Africa.
For their experiments the group collected cotton bollworm--also known as corn earworm or Helicoverpa zea-a species of moth that is a major agricultural pest and selected it for resistance against one of the Bt toxins Cry1ac.
when Carriã re's team put them on pyramided Bt cotton containing Cry2ab in addition to Cry1ac.
and some other pests that are not highly susceptible to Bt toxins to begin with. The team found violations of other assumptions required for optimal success of the pyramid strategy.
In particular inheritance of resistance to plants producing only Bt toxin Cry1ac was dominant which is expected to reduce the ability of refuges to delay resistance.
Refuges consist of standard plants that do not make Bt toxins and thus allow survival of susceptible pests Under ideal conditions inheritance of resistance is not dominant
According to Tabashnik overly optimistic assumptions have led the EPA to greatly reduce requirements for planting refuges to slow evolution of pest resistance to two-toxin Bt crops.
#Benefits of Bt corn go beyond rootworm resistanceengineered to produce the bacterial toxin Bt Bt corn resists attack by corn rootworm a pest that feeds on roots
But besides merely protecting against these losses the Bt trait has boosted also corn yields in some cases beyond normal expectations.
Fred Below and Jason Haegele of the University of Illinois at Urbana-Champaign set out to answer that question by determining how Bt corn uses nitrogen in the soil.
and with better root systems it's possible that Bt corn uses nitrogen differently than non-resistant strains the scientists hypothesized in turn affecting corn production.
The study published February 6 in Crop science showed just that--Bt corn had higher yields and used nitrogen more efficiently than non-resistant corn.
With its resistance to corn rootworm Below explains Bt corn has healthier and more active roots than corn without the resistance trait.
Additionally Bt corn would fare better at current levels of nitrogen use in the United states. In 2010 the average nitrogen application rate for corn production was around 140 lb/acre say Haegele and Below.
The healthy roots and efficient nutrient use of Bt corn could lead to changes in management practices that would further increase production.
With the Bt corn though you can protect the root system and grow more plants.
In addition to its utility in crop production Below is hopeful that Bt corn will open up new avenues of research as scientists begin to better understand root systems.
It has developed resistance to against more than 50 insecticides including DDT Bt toxins among others making the use of chemicals as a control measurement become ineffective.
Like his colleague Daniel Giddings Vassã£o Felipe Wouters is from Brazil where fall armyworm caused major losses of the maize yield before Bt maize was introduced.
According to a Reuters report this summer Brazilian farmers are complaining that Bt is not protecting the plants against the fall armyworm any longer.
The increasing resistance of pest insects to Bt is another reason to look deeper into the natural insect adaptations against plant defenses.
which was designed to make an insect-killing bacterial protein called Bt toxin. The results could have major impacts for managing pest resistance to Bt crops.
Bt crops have had major benefits for society said Jeffrey Fabrick the lead author of the study and a research entomologist at the USDA Agricultural research service in Maricopa Arizona.
By understanding how insects adapt to Bt crops we can devise better strategies to delay the evolution of resistance
and extend these benefits. Many mechanisms of resistance to Bt proteins have been proposed and studied in the lab
but this is the first analysis of the molecular genetic basis of severe pest resistance to a Bt crop in the field said Bruce Tabashnik one of the paper's authors and the head of the Department of Entomology in the UA College
of Agriculture and Life sciences. He also is a member of the UA's BIO5 Institute.
Based on laboratory experiments aimed at determining the molecular mechanisms involved scientists knew that pink bollworm can evolve resistance against the Bt toxin
and implement resistance management strategies such as providing refuges of standard cotton plants that do not produce Bt proteins and releasing sterile pink bollworm moths.
Planting refuges near Bt crops allows susceptible insects to survive and reproduce and thus reduces the chances that two resistant insects will mate with each other
As a result pink bollworm has been eradicated all but in the southwestern U s. Suppression of this pest with Bt cotton is the cornerstone of an integrated pest management program that has allowed Arizona cotton growers to reduce broad spectrum insecticide use by 80
In the U s. pink bollworm populations have not evolved resistance to Bt toxins in the wild. However resistant pink bollworm populations have emerged in India
which grows the most Bt cotton of any country in the world. Crops genetically engineered to produce proteins from the bacterium Bacillus thuringiensis
--or Bt--were introduced in 1996 and planted on more than 180 million acres worldwide during 2013.
Organic growers have used Bt proteins in sprays for decades because they kill certain pests but are not toxic to people and most other organisms.
Pest control with Bt proteins--either in sprays or genetically engineered crops--reduces reliance on chemical insecticides.
Although Bt proteins provide environmental and economic benefits these benefits are cut short when pests evolve resistance.
The emergence of resistant pink bollworm in India provided the researchers an opportunity to test the hypothesis that insects in the field would evolve resistance to Bt toxin by the same genetic mechanism found previously in the lab. In the lab strains the scientists had identified mutations in a gene
Binding of Bt toxin to cadherin is an essential step in the intoxication process. Mutations that disrupt cadherin block this binding
which leaves the insect unscathed by the Bt toxin. We wanted to see if field-resistant pink bollworm from India harbored these same changes in the cadherin gene Fabrick said.
Our findings represent the first example of alternative splicing associated with Bt resistance that evolved in the field said Fabrick who is also an adjunct scientist in the Department of Entomology at UA.
Mario Soberã n a Bt expert at the Universidad Nacional Autã noma de MÃ xico in Cuernavaca who was not an author of the study commented This is a neat example of the diverse mechanisms insect
An important implication is that DNA screening would not be efficient for monitoring resistance of pink bollworm to Bt toxins.
#Predators delay pest resistance to Bt cropscrops genetically modified with the bacterium Bt (Bacillus thuringiensis) produce proteins that kill pest insects.
Steady exposure has prompted concern that pests will develop resistance to these proteins making Bt plants ineffective.
Cornell research shows that the combination of natural enemies such as ladybeetles with Bt crops delays a pestâ##s ability to evolve resistance to these insecticidal proteins. â#oethis is demonstrated the first example of a predator being able
to delay the evolution of resistance in an insect pest to a Bt cropâ#said Anthony Shelton a professor of entomology at Cornell University's New york state Agricultural Experiment Station in Geneva N y
Bt is a soil bacterium that produces proteins that are toxic to some species of caterpillars
Bt genes have been engineered into a variety of crops to control insect pests. Since farmers began planting Bt crops in 1996 with 70 million hectares planted in the United states in 2012 there have been only three clear-cut cases in agriculture of resistance in caterpillars
and one in a beetle. â#oeresistance to Bt crops is said surprisingly uncommonâ Shelton. To delay or prevent insect pests from evolving resistance to Bt crops the U s. Environmental protection agency promotes the use of multiple Bt genes in plants
and the practice of growing refuges of non-Bt plants that serve as a reservoir for insects with Bt susceptible genes. â#oeour paper argues there is another factor involved:
the conservation of natural enemies of the pest speciesâ#said Shelton. These predators can reduce the number of potentially resistant individuals in a pest population and delay evolution of resistance to Bt.
In the study the researchers set up large cages in a greenhouse. Each cage contained Bt broccoli and refuges of non-Bt broccoli.
They studied populations of diamondback moth (Plutella xylostella) larvae a pest of broccoli and their natural enemies ladybird beetles (Coleomegilla maculata) for six generations.
Cages contained different combinations of treatments with and without predators and with and without sprayed insecticides on the non-Bt refuge plants.
Farmers commonly spray insecticides on refuge plants to prevent loss by pests but such sprays can kill predators and prey indiscriminately.
The results showed that diamondback moth populations were reduced in the treatment containing ladybird beetles and unsprayed non-Bt refuge plants.
Also resistance to Bt plants evolved significantly slower in this treatment. In contrast Bt plants with no refuge were defoliated completely in treatments without ladybirds after only four to five generations showing rapid development of resistance in the pests.
In the treatment with sprayed non-Bt refuge plants and predators diamondback moth populations were reduced
but the larvae more quickly evolved resistance to the Bt plants. â#oethese results demonstrate the effectiveness of Bt plants in controlling the pest population the lack of effect of Bt on the predators
and the role predators play in delaying resistance to Bt plants in the pest populationâ#said Shelton.
Story Source: The above story is provided based on materials by Cornell University. The original article was written by Krishna Ramanujan.
and cotton plants genetically engineered to produce proteins from the bacterium Bacillus thuringiensis (Bt). These proteins kill some key pests
Organic growers have used Bt toxins in sprays for decades and conventional farmers have adopted widely transgenic Bt crops since 1996.
In 2013 Bt corn and Bt cotton were planted on 187 million acres worldwide and accounted for 75%of all cotton
and 76%of all corn grown in the U s. Recognizing that resistance is not all
and use them to classify 13 cases of resistance to five Bt toxins in transgenic corn
and cotton based on monitoring data from five continents for nine major pest species. Emerging resistance of the western corn rootworm to Bt corn exemplifies the urgent need for well-defined
and cut back on soil insecticides U s. farmers began planting Bt corn that kills rootworms. The first evidence of rootworm resistance to Bt corn was discovered in Iowa in 2009 said Dr. Bruce Tabashnik the study's lead author
and head of the entomology department at the University of Arizona. Nearly five years later the resistance has spread
Although some scientists have expressed concern that reports of pest resistance to Bt crops provide'ammunition'to anti-biotech activists Tabashnik said Pests are remarkably adaptable.
and the adoption of transgenic Bt (Bacillus thuringiensis cotton which is modified to express its own pesticide the researchers found that the value of the pest control services dropped 79 percent from a high of $23. 96 million in 1990
and technological substitutes such as Bt cotton can affect the value of an ecosystem service even
The researchers point to mounting evidence of the evolution of pest resistance to Bt cotton suggesting that the value of bat pest control services may increase again.
This evidence of resistance evolution suggests that Bt cotton may not be a long-term solution to pest-related losses said Mccracken.
In fact by preying on the individual insects that survive the Bt toxin bats may provide the additional service of slowing the evolution of resistance to Bt and other insecticides.
studies showa large body of literature has shown that genetically-modified plants that produce proteins from the bacterium Bacillus thuringiensis (Bt) to protect themselves from insect pests have little to no effect on a wide range of nontarget insects.
However concerns about Bt crops still exist. Now two new studies using more exacting methods show that Bt crops have no negative effects on two beneficial insect predators or on a beneficial entomopathogenic nematode.
In an article in the February 2014 issue of Environmental Entomology called Using Resistant Prey Demonstrates that Bt Plants Producing Cry1ac Cry2ab
and Cry1f Have No Negative Effects on Geocoris punctipes and Orius insidiosus researchers used caterpillars that were known to be resistant to Bt proteins and fed them Bt maize and Bt cotton.
They then fed the caterpillars to two common beneficial predatory insects--insidious flower bugs (Orius insidiosus)
and big-eyed bugs (Geocoris punctipes)--for two generations and compared them to another group of predators that consumed caterpillars fed on non-Bt plants.
and fertility of the insect predators in both groups were similar regardless of whether they consumed caterpillars that fed on Bt plants or non-Bt plants.
This research demonstrates that the current Bt proteins used in corn and cotton crops globally do not harm Geocoris punctipes
By using caterpillars resistant to the Bt proteins in this study we were able to remove any'host quality effects'that might have led to spurious misinterpretation of the results.
This work demonstrated that the caterpillars consumed the Bt proteins and the predators consumed the Bt proteins
when they fed on the caterpillars but they did not suffer any harm even over multiple generations.
when it ingested another Bt protein. For this study resistant caterpillars were fed Bt broccoli and then exposed to Heterorhabditis bacteriophora a beneficial nematode that preys on insects.
The researchers found that the virulence reproductive potential and time of emergence of the nematodes that consumed Bt-fed caterpillars were affected not significantly compared to nematodes that did not ingest the Bt protein.
This is the first report we are aware of in which a nematode predator has been tested in such detail against a Bt protein Dr. Shelton said.
Together these two studies add to the scientific literature demonstrating that Bt plants can control targeted insect pests
while not harming important natural enemies that help suppress pest species and maintain biodiversity in agricultural systems Shelton added.
The study is described in an article called Comparative Diversity of Arthropods on Bt Maize and Non-Bt Maize in two Different Cropping Systems in South africa
which appears in the February 2014 issue of Environmental Entomology. The aims of the study were to compile a checklist of arthropods that occur on maize in South africa
and abundance of arthropods and functional groups on Bt maize and non-Bt maize the authors wrote.
and diversity of arthropods in maize and the different functional guilds were affected not significantly by Bt maize either in terms of diversity or abundance.
A total of 8771 arthropod individuals comprising 288 morphospecies were collected from 480 plants sampled from Bt maize and non-Bt maize fields over a two-year period.
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