Scientists Confirm Failures of Bt-Crops

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26 Sep 2005 14:07:10 -0000

 

Scientists Confirm Failures of Bt-Crops

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ISIS Press Release 26/09/05

 

Scientists Confirm Failures of Bt-Crops

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Ineffective against insect pests, harmful to health and

biodiversity, yield drag, pest resistance. Dr. Mae-Wan Ho

 

A fully referenced version of this paper is posted on ISIS

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http://www.i-sis.org.uk/full/SCFOBTCFull.php.

Details here http://www.i-sis.org.uk/membership.php

 

Farmers were first

 

Scientific studies from many countries have now backed up

what farmers have known for years, that Bt crops –

genetically engineered with Bt toxin proteins from the soil

bacterium Bacillus thuringiensis targeted at insect pests -

often failed to protect against pest attacks, and have other

problems as well.

 

Scientists in India, China and the United States found that

the levels of Bt toxin produced by Bt crops vary

substantially in different parts of the plant and in the

course of the growing season, and are often insufficient to

kill the targeted pests. This could lead to greater use of

pesticides, and accelerate the evolution of pest resistance

to the Bt toxin. Pest resistance to a Bt toxin has indeed

arisen in the field in Australia.

 

The Bt toxins are a family of similar Cry proteins

identified by numbers and letters. Each Cry protein differs

somewhat in amino acid sequence and targets specific pests.

 

India

 

Scientists at the Central Institute of Cotton Research

studied Bt cotton hybrids approved for commercial planting

in India: Bollgard-MECH-12, Bollgard-MECH-162, Bollgard-

MECH-184, Bollgard-RCH-2, Bollgard-RCH-20, Bollgard-RCH-134,

Bollgard-RCH-138 and Bollgard-RCH-144. All the varieties

were created by using Indian parent-varieties to which the

crylAc gene was introduced from the Bt-cotton variety, Coker

312, ultimately derived from transformation event MON531

(Monsanto).

 

The researchers found that the amount of Cry1Ac protein

varied across the varieties and between different plant

parts. The leaves had the highest levels; whereas the levels

in the boll-rind, square bud and ovary of flowers were

clearly inadequate to fully protect the fruiting parts

producing the cotton bolls. Increasing numbers of armyworm

(Helicopverpa armigera) larvae survived as toxin levels went

below 1.8 microg /g wet weight of the plant parts. Thus, a

critical level of 1.9 microg/g was needed to kill all the

pests. Regardless of plant varieties, the level of toxin

decreased with the age of the plant, though the decrease was

more rapid in some hybrids than in others. By 110 days,

Cry1Ac expression decreased to less than 0.47microg/g in all

hybrids.

 

In a separate study, scientists at the same institute tested

the susceptibility of an insect pest from different regions

in India to Bt toxin [2]. They took samples of larvae of

the spotted bollworm, Earias vitella from 27 sites in 19

cotton-growing districts of North, Central and South India

during the 2002 and 2003 cropping seasons and tested their

susceptibility to Cry 1Ac toxin protein purified from E.

coli strains expressing the recombinant protein. The LC50 -

the concentration killing 50 percent of the larvae – of

Cry1Ac ranged from 0.006 to 0.105 microg/ml. There was a

17.5 fold overall variability in susceptibility among the

districts. The highest variability of 17.5 fold was recorded

from districts of South India. The variability in pest

susceptibility, like the variable expression of the Cry1A

proteins in Bt crops, will reduce the efficacy of Bt pest

control.

 

However, using recombinant CrylA proteins from bacteria to

test for susceptibility in pests can be entirely misleading

(see below).

 

China

 

A study was carried out in the Institute of Plant

Protection, Chinese Academy of Agricultural Sciences in

Beijing on two Bt cotton varieties: GK19, with a

Cry1Ac/Cry1Ab fused gene, developed by the Biotechnology

Research Institute of Chinese Academy of Agricultural

Sciences, and BG1560, with a Cry1Ac gene, supplied by

Monsanto [3]. The test site was in Tianmen County, Hubei

Province, an intensive planting area in the middle of the

Yantze River valley. The results showed that the toxin

content in the Bt cotton varieties changed significantly

over time, depending on the part of the plant, the growth

stage and the variety. Generally, the toxin protein was

expressed at high levels during the early stages of growth,

declined in mid-season, and rebounded late in the season. In

line with the study in India, the scientists found that the

toxin content in leaf, square, petal and stamens were

generally much high than those in the ovule and the boll.

The researchers pointed out that such variability in toxin

expression could accelerate the development of pest

resistance to the toxin.

 

USA

 

Scientists at the Southern Insect Management Research Unit

of the United States Department of Agriculture (USDA)

studied both Bt maize hybrids expressing Cry1Ab (such as

event MON810) and Bt cotton varieties expressing Cry1Ac

(such as event MON531) [4].

 

They found that Cry1Ab was variable depending on location in

the same leaf as well as between leaves at different stage

of growth. The tips of maize leaf at the V7 stage had a

higher concentration compared with the middle section of the

leaf, and the middle section of the V9 leaf had the lowest

concentration. Also, the green tissues richest in

chlorophyll had the highest toxin levels, the yellow-green

tissues with reduce chlorophyll had less, and the white-

yellow tissues poorest in chlorophyll had the least. The

weight of fall armyworm larvae measured at day 5 of feeding

showed a decrease that was significantly correlated with the

amount of toxin present in the plant material, while there

was 100 percent mortality in the southwestern corn borer

larvae regardless of the level of toxin in the plant

tissues.

 

In the Bt cotton, the level of CrylAc was significantly

lower in boll tips where flowers had remained attached,

compared with normal boll tips. Boll tips where the flowers

remained attached are often the sites at which corn

earworms, Helicopverpa zea (Boddie) penetrate Bt cotton

bolls. In both Bt maize and Bt cotton, tissues that had low

chlorophyll content also had reduced Cry1A proteins.

 

The US Environment Protection Agency recommends planting a

certain percent of crop area with non-Bt varieties to serve

as `refuge', in order to ensure that enough susceptible

insects are produced to limit the evolution of resistance.

An important requirement for the refuge strategy to work

effectively is a high level of expression of the toxin, so

heterozygous insects (those with one copy of resistance

gene) will fail to survive to reproduce. Thus, any reduction

from high toxin levels will compromise the refuge strategy

and the effectiveness of Cry1A proteins in pest control.

 

Researchers at the University of Arizona Tucson and the

Arizona Cotton Research and Protection Council, Phoenix had

found a " surprisingly high " frequency (0.16) of the Cry1Ac

resistance gene in field populations of the pink bollworm in

Arizona in 1997, which did not appear to increase further as

expected in 1998 or 1999 [5]. However, the tests were done

with the recombinant Cry1Ac protein produced in the

bacterium, Pseudomonas fluroescens, and not from the Bt

cotton plant, and could be giving entirely misleading

results on the evolution of resistance in the field ( " No Bt

resistance? " SiS20 http://www.i-sis.org.uk/isisnews.php)

[6].

 

Bt resistance in Australia

 

A population of the Australian cotton bollworm, Helicoverpa

armigera – the most important agricultural pest in Australia

as well as China, India and Africa - has developed

resistance to Cry1Ac at 275-times the level that would have

killed the non-resistant insect [7]. Some 70 percent of the

resistant larvae were able to survive on Bt cotton

expressing Cry1Ac (Ingard). The resistance is inherited as

an autosomal semi-dominant trait (the heterozygote with one

copy of the resistance gene is half as resistant as the

homozygotes with two copies of the resistance gene).

 

Bt cotton varieties expressing Cry1Ac (Ingard) have been

grown in Australia to control the cotton bollworm since

1996, and a new variety containing both Cry1Ac and Cry2Ab

was commercially released in late 2003. Resistance

monitoring in Australia and China had suggested that pest

susceptibility to Cry1Ac was declining in the field. In

2001, a strain of cotton bollworm was isolated from the

survivors in the New South Wales and Queensland monitoring

programme that appeared to be resistant to Cry1Ac. The

researchers have now confirmed the findings, and attributed

the high level of resistance to a 3- to 12-fold over-

expression of an enzyme, serine protease, which binds avidly

to Cry1Ac toxin, preventing it from acting, and possibly,

detoxifying it by breaking it down.

 

Canadian scientists find yield and economic disadvantage in

Bt maize

 

Researchers at the Eastern Cereal and Oilseed Research

Centre, Agriculture and Agri-Food Canada, Ottawa, Ontario,

carried out a field experiment over three years to compare

commercial corn hybrids with their corresponding Bt-hybrids

belonging to the Monsanto and Syngenta [8]. They found that

some of the Bt hybrids took 2-3 additional days to reach

silking and maturity and produced a similar or up to 12

percent lower grain yields, with 3-5 percent higher grain

moisture content at maturity in comparisons with their non-

Bt counterparts. Higher grain moisture content increases

drying cost. Bt hybrid seeds also have a $25-30 premium per

ha.

 

The economic disadvantages are dwarfed in comparison with

impacts on biodiversity and human and animal health that

have been known for years, however (see below: also " Bt risks

negligible " SiS 2002, 13/14

http://www.i-sis.org.uk/isisnews.php).

 

Bt maize more woody

 

It has been known for some time that genetic modification is

full of pitfalls, among which are many unintended effects. A

paper published in 2001 [9] reported that the content of

lignin (woody substances) was high by 33 to 97 percent in

the Bt maize varieties tested: Bt11, Bt176 and Mon810. Now,

researchers at environmental and agricultural institutes in

Leipzig, Aachen and Muncheberg, Germany, and the University

of Waterloo in Ontario, Canada, have confirmed increases in

lignin in two Bt maize lines, Novelis (event MON00810-6,

from Monsanto) and Valmont (event SYN-EV176-9, from

Syngenta), compared with their respective isogenic

varieties, Nobilis and Prelude, all grown under identical

conditions [10]. The increases in lignin are more modest,

and are restricted to the stems of the plants: Novelis by 28

percent over Nobilis, and Valmont by 18 percent over

Prelude.

 

Increase in lignin content will impact on the digestibility

of the plant for livestock, it also decreases the rate at

which the plant material break down, affecting nutrient

recycling, the soil microbial community, and soil carbon

balance.

 

Intriguingly, an earlier report has also found increased

lignin in Monsanto's Roundup Ready soya, genetically

modified to be tolerant to the herbicide Roundup [11], which

caused the stem to split open in hot climate and crop losses

of up to 40 percent.

 

These results suggest that genetic modification per se may

be increasing lignin content, perhaps as a response to

metabolic stress from the high levels of transgene

expression driven by aggressive viral promoters.

 

Impacts on biodiversity and health

 

Bt toxins are known to harm beneficial/endangered insect

species and soil decomposers [12]:

 

 

Pollen from Bt-maize was lethal to the larvae of the monarch

butterfly.

 

Increased mortality of lacewing larvae fed on artificial

diet containing Bt-maize or on corn-borer larvae that had

eaten Bt-corn.

 

Bt sprays used to reduce caterpillars in forests led to

fewer black-throated blue warbler nests.

 

A parasite of corn-borers, Macrocentris cingulum, was found

to be reduced in Bt-cornfields compared with non-Bt corn

fields.

 

One preparation of Bt (var. tenebrionis), reported to be

specific for Coleoptera, caused significant mortality in

domestic bees.

 

Soil-dwelling collembola, Folsomia candida, an important

decomposer, suffered significant mortality from transgenic

maize with Cry1Ab.

 

Bt not only remains in the soil with Bt-plant debris, it is

actively exuded from the plant roots where it binds to soil

particles and persists for 180 days or more, so its effects

on soil decomposers and other beneficial arthropods may be

extensive.

 

Bt-toxins are actual and potential allergens for human

beings. Field workers exposed to Bt spray experienced

allergic skin sensitization and induction of IgE and IgG

antibodies to the spray [13]. Recombinant Cry1Ac protoxin

was found to be a potent mucosal immunogen, as potent as

cholera toxin [14]. A Bt strain that caused severe human

necrosis (tissue death) killed mice infected through the

nose within 8 hours, from clinical toxic-shock syndrome

[15]. Both Bt protein and Bt-potato harmed mice in feeding

experiments [16]. All Bt-toxins along with many other

transgenic proteins exhibit similarities to known allergens

and are hence suspected allergens until proven otherwise

( " Are transgenic proteins allergenic? " SiS 25

http://www.i-sis.org.uk/isisnews.php) [17-19].

 

Recently, much publicity has been given to a report from

scientists in Portugal published in the house journal of the

American Academy of Allergy, Asthma and Immunology, because

it claimed " lack of allergenicity of transgenic maize and

soya samples " [20].

 

A careful reading of the report reveals, however, that the

researchers had no evidence that the small number of

subjects they tested have ever been exposed to transgenic

maize and soya. They wrote: " Bearing in mind that since

1998 all the GM products under testing were approved for

commercialisation in the European Union.., we assumed that

consumption of maize and soya food-derived products implied

a consumption of GM soya and maize. " (emphasis added).

Moreover, the tests performed were limited to skin pricks

and IgE antibodies, both known to be limited in reliability

[21]. Most of all, there are many allergies that do not

involve IgE antibodies [22].

 

Nevertheless, the researchers stated, " In this study we did

not obtain any differential positive results, which allows

us to conclude that the transgenic products under testing

seem to be safe regarding their allergenic potential. "

(emphasis added).

 

 

 

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