Insecticide resistance caused by recombination of 2 genes

Novel enzyme makes cotton bollworm resistant against pyrethroids

2012-09-12

(Press-News.org) Helicoverpa armigera: a global pest

Larvae of the cotton bollworm (Helicoverpa armigera) are dreaded pests all over the world. They have a very wide host range: About 200 different plant species are known as potential food for the voracious insect. The herbivore attacks crops in Africa, South Europe, India, Central Asia, New Zealand, and Australia. Nearly 30% of all globally used insecticides − Bt toxins as well as pyrethroids − are applied to protect cotton and other crops against the bollworm.

Resistance to pyrethroids

Pyrethroids are synthetic substances based on compounds of the natural insecticide pyrethrum in Tansy flowers (Tanacetum). They have been successfully applied in fruit, vegetable and crop farming for decades. In cotton bollworms, development of resistance to the particularly effective pyrethroid fenvalerate was observed in Australia since 1983. In 1998, David Heckel, who became director at the Max Planck Institute for Chemical Ecology in 2004, mapped the location of the resistance gene in the genome of the insect for the first time. This gene locus was later found to encode a P450 monooxygenase enzyme. These so-called cytochrome P450 (CYP) enzymes are also known in human medicine, because they can render toxins or pharmaceuticals ineffective by metabolizing the active molecule.

Nicole Joußen, scientist at the institute and expert on P450 enzymes, studied the Helicoverpa armigera strain "TWB" resistant to fenvalerate. She could identify the P450 monooxygenase in this strain, suspected to mediate pyrethroid resistance. After cloning larger genome regions, DNA sequencing, and performing crossing experiments as well as biochemical analyses, she was surprised to find that of the seven P450 enzymes only one, CYP337B3, hydroxylates the fenvalerate molecule to 4'-hydroxyfenvalerate. This chemical reaction increases the resistance to this toxin 42-fold: A LD50 value of 1.9 µg of fenvalerate was measured in resistant TWB larvae, whereas half of the non-resistant caterpillars died after intake of only 0.04 µg of the toxin.

Unequal Crossing-Over led to the formation of the CYP337B3 Gene

The CYP337B3 gene was formed in a very special way: by a process called "unequal crossing-over" by geneticists. If very similar DNA sequences, for example transposable elements, get in contact with one another during the division of cell nuclei, novel gene combinations occur. As a consequence, some of the genetic information is lost on one DNA strand, and new genetic information is inserted and sometimes even doubled on the other strand. This natural process is important for the evolution of gene families, as could now be observed in the case of the CYP337B3 gene. "For the first time, our results reveal a mutation mediating resistance to an insecticide, which is caused by a crossing-over event," says David Heckel. The scientists studied CYP337B3 and found that the gene consists of parts of two other P450 genes, B1 and B2, encoding enzymes neither of which can detoxify fenvalerate. The unique combination of parts of the B1 and B2 precursor genes in the chimeric B3 gene is responsible for the new capability of the P450 enzyme to bind, hydroxylate, and finally detoxify the insecticide.

Once the CYP337B3 gene was formed, spraying cotton bollworms with pyrethroids caused its frequency in the population to gradually increase. This resistance was successfully delayed in Australia by restricting the use of pyrethroids to once per year, and using other insecticides at other times. This contrasts with the situation in other cotton-growing countries, where pyrethroids were overused, resistance rapidly developed, and then pyrethroids became ineffective against the bollworm. [AO/JWK]

###Original Publication:

Nicole Joußen, Sara Agnolet, Sybille Lorenz, Sebastian E. Schöne, Renate Ellinger, Bernd Schneider, David G. Heckel (2012). Resistance of Australian Helicoverpa armigera to fenvalerate is due to the chimeric P450 enzyme CYP337B3. Proceedings of the National Academy of Sciences USA, Early Edition, 4. September 2012. DOI: 10.1073/pnas.1202047109.

Further Information:

Dr. Nicole Joußen, njoussen@ice.mpg.de, +49-(0)3641-57 1552

Prof. Dr. David G. Heckel, heckel@ice.mpg.de, +49-(0)3641-57 1501

Picture Requests: Angela Overmeyer M.A., +49 3641 57-2110, overmeyer@ice.mpg.de or download from http://www.ice.mpg.de/ext/735.html

ELSE PRESS RELEASES FROM THIS DATE:

Nationwide Children's Hospital develops prototype for safer, child-resistant spray bottle

2012-09-12

VIDEO: Studies show that when it comes to household cleaners, the spray bottle is the most common source of exposure to injury among children in the US Not only have children... Click here for more information. Researchers at The Research Institute at Nationwide Children's Hospital, in partnership with The Ohio State University have developed a prototype for child-resistant spray bottles for household cleaning products. If produced, the prototype would provide an alternative ...

Forensic science on trial

2012-09-12

The key player in a movement challenging improper use of DNA testing and other elements of forensic science is the topic of a compelling cover story in this week's edition of Chemical & Engineering News. The story in the weekly newsmagazine of the American Chemical Society (ACS) — the world's largest scientific society — features the Innocence Project, which, in the last two decades, has helped free nearly 300 wrongfully convicted prisoners. C&EN Senior Editor Carmen Drahl uses a symposium on the Innocence Project held at ACS' Fall National Meeting & Exposition to discuss ...

An advance toward a flu-fighting nasal spray

2012-09-12

In an advance toward development of a nasal spray that protects against infection with influenza and spread of the disease, scientists are reporting identification of a substance that activates the first-line defense system against infection inside the nose. They describe effects of a synthetic form of a natural substance found in bacterial cell walls in ACS' journal Molecular Pharmaceutics. David C. Jackson and colleagues explain that the body's so-called innate immune system forms a first-line defense system against respiratory diseases like influenza A — which causes ...

Record 4.02 billion prescriptions in United States in 2011

2012-09-12

People in the United States took more prescription drugs than ever last year, with the number of prescriptions increasing from 3.99 billion (with a cost of $308.6 billion) in 2010 to 4.02 billion (with a cost of $319.9 billion) in 2011. Those numbers and others appear in an annual profile of top prescription medicines published in the journal ACS Chemical Neuroscience. Journal Editor-in-Chief Craig W. Lindsley analyzed data on 2011 drugs with a focus on medications for central nervous system (CNS) disorders. So-called antipsychotic medicines — including those used to ...

New analysis of drinking water-related gastrointestinal illness

2012-09-12

The distribution system piping in U.S. public water systems that rely on non-disinfected well water or "ground water" may be a largely unrecognized cause of up to 1.1 million annual cases of acute gastrointestinal illness (AGI), involving nausea, vomiting and diarrhea, scientists are reporting. Their study in ACS' journal Environmental Science & Technology concludes that such illnesses may become more of a problem as much of the nation's drinking water supply system continues to age and deteriorate. Frank J. Loge, Mark A. Borchardt and colleagues explain that more than ...

Russia fails to grasp democratic ideals

2012-09-12

EAST LANSING, Mich. — The brutally repressive Soviet Union Vladimir Shlapentokh left behind 33 years ago may have opened its borders to the world, but today's Russia has become wracked with greed, corruption and mass emigration that threaten the nation's future. So argues Shlapentokh, a Michigan State University sociologist, in the academic journal Communist and Post-Communist Studies. "As Russia's plight shows, the assumption that openness and liberalization automatically promote democracy and guarantee it will function turned out to be wrong," Shlapentokh said. "It ...

Himalayan glaciers retreating at accelerated rate in some regions but not others

2012-09-12

WASHINGTON -- Glaciers in the eastern and central regions of the Himalayas appear to be retreating at accelerating rates, similar to those in other areas of the world, while glaciers in the western Himalayas are more stable and could be growing, says a new report from the National Research Council. The report examines how changes to glaciers in the Hindu Kush-Himalayan region, which covers eight countries across Asia, could affect the area's river systems, water supplies, and the South Asian population. The mountains in the region form the headwaters of several major ...

Math anxiety causes trouble for students as early as first grade

2012-09-12

Many high-achieving students experience math anxiety at a young age — a problem that can follow them throughout their lives, new research at the University of Chicago shows. In a study of first- and second-graders, Sian Beilock, professor in psychology, found that students report worry and fear about doing math as early as first grade. Most surprisingly math anxiety harmed the highest-achieving students, who typically have the most working memory, Beilock and her colleagues found. "You can think of working memory as a kind of 'mental scratchpad' that allows us to 'work' ...

Stress hormones: Good or bad for posttraumatic stress disorder risk?

2012-09-12

Philadelphia, PA, September 12, 2012 – Glucocorticoids, a group of hormones that includes cortisol, are considered stress hormones because their levels increase following stress. When their relationship to stress was first identified, it was shown that the release of cortisol prepared the body to cope with the physical demands of stress. Subsequently, high levels of cortisol were linked to depression and other stress-related disorders, giving rise to the hypothesis that high levels of cortisol on a long-term basis may impair the psychological capacity to cope with stress. ...

New model could help fill data gap in predicting historical air pollution exposure

2012-09-12

MEDFORD/SOMERVILLE, MASS. – In a study that analyzed relationships between air quality and unemployment levels, a Tufts University researcher has developed a new statistical model that retrospectively estimates air pollution exposure for previous time periods where such information is not available. Mary Davis, an associate professor of urban and environmental policy and planning at Tufts University School of Arts and Sciences, analyzed traffic-related air pollution levels and unemployment rates in four separate regions of California for which extensive air monitoring ...

Adolescent boys who experience violence have up to 8 times the odds of perpetrating physical and sexual intimate partner violence that same day, per South African study collecting real-time data over

Critically endangered hawksbill turtles migrate up to 1,000km from nesting to foraging grounds in the Western Caribbean, riding with and against ocean currents to congregate in popular feeding hotspot

Insecticide resistance caused by recombination of 2 genes

ELSE PRESS RELEASES FROM THIS DATE:

LAST 30 PRESS RELEASES: