Researchers identify insect resistance to Bt pesticide

Aug 30, 2011 By Krishna Ramanujan
Researchers identify insect resistance to Bt pesticide
Cabbage looper larvae, Trichoplusia ni, feeding on transgenic broccoli plants expressing an insecticidal protein (Cry1Ac) from the biological pesticide Bacillus thuringiensis (Bt). (Ping Wang)

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 by destroying their guts. Insects in the field develop resistance to it, however, via a that alters a toxin receptor in the insect's gut, two Cornell have discovered. The receptor belongs to a class of 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 and senior author of the paper published online in the Aug. 15 issue of the . 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.

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.

Explore further: Telling the time of day by color

Related Stories

Study uncovers optimal ecology of bioinsecticide

May 20, 2010

Researchers at the University of Oxford and Royal Holloway University of London have discovered that the commonly used and naturally occurring bacterial insecticide Bt works best if applied to young plants ...

Transgenic maize is more susceptible to aphids

Aug 29, 2007

The environmental consequences of transgenic crops are the focus of numerous investigations, such as the one published in the journal PloS ONE, which was carried out by Cristina Faria and her colleagues, under the supervision ...

Recommended for you

Telling the time of day by color

Apr 17, 2015

Research by scientists at The University of Manchester has revealed that the colour of light has a major impact on how the brain clock measures time of day and on how the animals' physiology and behavior adjust accordingly. ...

Aphrodisiac for fish and frogs discovered

Apr 17, 2015

A supplement simply added to water has been shown to boost reproduction in nematodes (roundworms), molluscs, fish and frogs – and researchers believe it could work for humans too.

Evolution puts checks on virgin births

Apr 17, 2015

It seems unnatural that a species could survive without having sex. Yet over the ages, evolution has endowed females of certain species of amphibians, reptiles and fish with the ability to clone themselves, ...

Humans can't resist those puppy-dog eyes

Apr 16, 2015

When humans and their four-legged, furry best friends look into one another's eyes, there is biological evidence that their bond strengthens, researchers report.

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

wiyosaya
not rated yet Aug 30, 2011
Quite interesting in the context of this story www.physorg.com/n...ugs.html that details another insect resisting Bt.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.