THIRD WORLD NETWORK BIOSAFETY INFORMATION SERVICE
Dear Friends and Colleagues
Bt Crops May Speed Up Spread of Pests
Two recent studies show that the cultivation of transgenic insecticidal plants can speed up the spread of specific plant pests. The research was carried out with cotton and soybeans genetically engineered (GE) to produce Bt toxins. In China, cotton bollworm is spreading rapidly in fields where Bt cotton is grown. In Brazil, white flies are becoming increasingly problematic in Bt soybean fields. This is affecting both farmers and agro-ecosystems. (Item 1)
The research in China (Item 2) shows that if cotton bollworms are infected with specific viruses, they spread particularly rapidly in Bt cotton fields. These viruses appear to stimulate the immune system of the larvae, thereby reducing the toxicity of the Bt toxins, thus enabling the larvae to acquire resistance to the toxin more rapidly and demonstrate higher fitness than others of the same species not infected with these viruses. The research further shows that the infected larvae are rarely found in fields where conventional cotton is grown. The infected bollworms are only spreading in fields where Bt cotton is grown.
In Brazil (Item 3), populations of white flies are increasing in fields where GE Bt soybeans are grown. Laboratory studies found that the white flies suck fluid from the plants and appear to benefit from specific biological characteristics of the GE soybeans. This finding seems to be especially true for glyphosate-resistant GE soybeans which also produce Bt toxins: insects feeding on these plants showed higher fecundity and a significant increase in the number in offspring. These effects were not observed if the GE soybeans were only resistant to glyphosate. The higher incidence of white flies also promotes plant diseases; the white flies transmit plant viruses when they feed on the plants and their excretions facilitate the occurrence of fungal diseases.
These two studies join several others which have reported unexpected negative environmental effects associated with GE plant cultivation, showing that the risks to ecosystems caused by the mass release of GE plants not derived from evolutionary processes, are much more complex than originally thought. Such interactions between GE plants and their environment are not sufficiently taken into account in risk assessment.
With best wishes,
Third World Network
131 Jalan Macalister
10400 Penang
Malaysia
Email: twn@twnetwork.org
Websites: http://www.twn.my/and http://www.biosafety-info.net/
To subscribe to other TWN information services: www.twnnews.net
———————————————————————————————
Item 1
HOW DO GENETICALLY ENGINEERED CROPS SPEED UP THE SPREAD OF PLANT PESTS?
Adverse environmental effects in insecticidal Bt plant cultivation
Testbiotech
23 March 2021
https://www.testbiotech.org/en/news/how-do-genetically-engineered-crops-speed-spread-plant-pests
Recent Chinese and Brazilian studies strongly indicate that the cultivation of transgenic insecticidal plants can speed up the spread of specific plant pests. Unexpected and complex environmental interactions play a crucial role in this context.
The research was carried out with genetically engineered (GE) cotton and soybeans that produce so-called Bt toxins. These insecticidal proteins occur naturally in soil organisms (Bacillus thuringiensis). In China, cotton bollworm is spreading rapidly in fields where Bt cotton is grown. In Brazil, so-called white flies are becoming increasingly problematic in Bt soybean fields. This is affecting both farmers and agro-ecosystems.
The research in China (published as preprint) shows that if cotton bollworms (Helicoverpa armigera) are infected with specific viruses they spread particularly rapidly in Bt cotton fields. These viruses appear to stimulate the immune system of the larvae: the toxicity of the Bt toxins is reduced thus enabling the larvae to acquire resistance to the toxin more rapidly and, at the same time, have higher fitness than others of the same species not infected with these viruses. The research further shows that the infected larvae are rarely found in fields where conventional cotton is grown. The infected bollworms are only spreading in fields where Bt cotton is grown. According to the authors, their findings show that interactions between GE plants, insects and microorganisms deserve more attention. Currently, these complex interactions are hardly taken into account in environmental risk assessment.
In Brazil, populations of white flies (Bemisia tabaci) are increasing in fields where insecticidal GE soybeans are grown. Originally this was thought to be because of a reduction in the spraying of insecticides. However, laboratory experiments revealed other findings: the white flies suck fluid from the plants and appear to benefit from specific biological characteristics of the GE soybeans. This finding seems to be especially true for glyphosate-resistant GE soybeans which also produce Bt toxins: insects feeding on these plants showed higher fecundity and a significant increase in the number in offspring. These effects were not observed if the GE soybeans were only resistant to glyphosate.
The higher incidence of white flies also promotes plant diseases: the white flies transmit plant viruses when they feed on the plants and their excretions facilitate the occurrence of fungal diseases. The authors of the study state that the causes of the strongly increased number of white flies are unknown. One possibility: the Bt insecticides, which are not toxic for the white flies, might have stimulating effects. Unexpected interactions in the genome of the soybean varieties are also being considered.
It is not the first time that an increased spread of pest insects in Brazilian GE soybean has been reported: Monsanto experts warned in 2014 that another pest insect, the southern armyworm (Spodoptera eridania), was increasingly spreading in fields with GE soybeans engineered to be resistant to glyphosate and produce Bt toxins.
Several publications have in recent years reported unexpected negative environmental effects associated with GE plant cultivation. Testbiotech believes that the interactions between GE plants and their environment are not sufficiently taken into account in risk assessment. Furthermore, the risks to ecosystems caused by the mass release of GE plants not derived from evolutionary processes, are much more complex than originally thought.
Contact:
Christoph Then, info@testbiotech.org, Tel +49 (0) 151 54638040
Item 2
RAPID SPREAD OF A SYMBIOTIC VIRUS IN A MAJOR CROP PEST FOLLOWING WIDE-SCALE ADOPTION OF BT-COTTON IN CHINA
Yutao Xiao et al.
BioRxiv
Preprint posted 10 Feb 2021
https://doi.org/10.1101/2021.02.08.430243
https://www.biorxiv.org/content/10.1101/2021.02.08.430243v1.full
Abstract
Bacillus thuringiensis (Bt) crops have been widely planted and the effects of Bt-crops on populations of the target and non-target insect pests were well studied. However, the effects of Bt-crops exposure on microorganisms that interact with crop pests haven’t previously been quantified. Here, we use laboratory and field data to show that infection of Helicoverpa armigera with a symbiotic densovirus (HaDV2) is associated with its enhanced growth and resistance to Bt-cotton. Moreover, field monitoring showed a much higher incidence of cotton bollworm infection with HaDV2 in regions cultivated with Bt-cotton than in regions without it, with the rate of densovirus infection increasing with increasing use of Bt-cotton. RNA-seq suggested resistance to both baculovirus and Cry1Ac were enhanced via the immune-related pathways. These suggest that the exposure to Bt-crops has selected for beneficial interactions between the target pest and a symbiotic microorganism that enhances its performance on Bt-crops under field conditions.
————————————————————————————–
Item 3
PLANT RESISTANCE IN SOME MODERN SOYBEAN VARIETIES MAY FAVOR POPULATION GROWTH AND MODIFY THE STYLET PENETRATION OF BEMISIA TABACI (HEMIPTERA: ALEYRODIDAE)
Mauricélia F Almeida et al.
Journal of Economic Entomology, toab008
24 Feb 2021
https://doi.org/10.1093/jee/toab008
https://academic.oup.com/jee/advance-article-abstract/doi/10.1093/jee/toab008/6149198
Abstract
Complaints of severe damage by whiteflies in soybean fields containing genetically engineered (GE) varieties led us to investigate the role of transgenic soybean varieties expressing resistance to some insects (Cry1Ac Bt toxin) and to herbicide (glyphosate) on the population growth and feeding behavior of Bemisia tabaci (Gennadius) MEAM1 (Hemiptera: Aleyrodidae). In the laboratory, the whiteflies reared on the GE Bt soybeans had a net reproductive rate (R0) 100% higher and intrinsic rate of population increase (rm) 15% higher than those reared on non-GE soybeans. The increased demographic performance was associated with a higher lifetime fecundity. In electrical penetration graphs, the whiteflies reared on the GE soybeans had fewer probes and spent 50% less time before reaching the phloem phase from the beginning of the first successful probe, indicating a higher risk of transmission of whitefly-borne viruses. Data from Neotropical fields showed a higher population density of B. tabaci on two soybean varieties expressing glyphosate resistance and Cry1Ac Bt toxin. These results indicate that some GE soybean varieties expressing insect and herbicide resistances can be more susceptible to whiteflies than non-GE ones or those only expressing herbicide resistance. Most likely, these differences are related to varietal features that increase host-plant susceptibility to whiteflies. Appropriate pest management may be needed to deal with whiteflies in soybean fields, especially in warm regions, and breeders may want to consider the issue when developing new soybean varieties.