'Bt' insecticide-generating GM crops are sold as a major weapon in the battle against key species of pest without the need for chemical applications.
The initial benefits of Bt are eroded within a few years, not only by the evolution of resistance in the target pests, but by Bt-resistant non-target pests which are happy to fill the vacant seat at the monoculture banquet.
Early on, we had reports of out-of-control mealy bugs on Bt crops in India and Pakistan [1] and mirid bugs in China [2]. These are assumed to be the result of reduced spraying with broad-spectrum insecticides thanks to Bt.
However, there are some much more complicated environmental interactions going on. For example, mirid bugs were previously minor pests on cotton until the Bt GM version came along.
More recent reports are of whitefly which are causing severe damage to Bt soya in Brazil because the reproduction of these sap-suckers is measurably boosted in the GM crop. Studies have shown that this success is linked to the increased ease with which the pests can penetrate the plant to reach the 'phloem' channels where the sap flows.
It seems that these Bt plants have a less robust epidermis (outer skin) and possibly more nutritious sap for the flies to feed on.
It's always been assumed that, since the Bt toxin is produced by plant tissues and isn't present in the sap, sap-feeding insects won't be exposed to it. However, it's been pointed out that, as the flies penetrate through to the GM plant tissue to reach the sap, they are exposed to low levels of the toxin. The stress of contact with sub-lethal amounts of a toxin are notorious for stimulating reproduction in insects.
Even more complicated is what's happening in Brazil's Bt cotton fields where the bollworms targeted by the GM toxin are becoming increasingly resistant.
Scientists there have discovered that the pests seem to be helped by the presence of a non-pathogenic virus. Virus-infected bollworms not only have increased resistance to the Bt insecticide, but mature faster and have enhanced reproduction.
There's evidence that the virus' action is to activate immune and developmental biochemical pathways in the bollworms.
It seems subtle changes in the structure of GM plants can make them more susceptible to biotic stress, and the Bt toxin itself, in the wrong quantities, can promote pests.
Moreover, while virologists direct all their attention to pathogenic viruses, there's clearly a vast scope for unrecognised friendly viruses to be giving Nature a helping hand and GM plants a slap in the face.
Tell your food and farming regulators to ditch the simplistic notion that humanly-designed 'fixes' for complex problems in a complex environment will ever work as humanly intended, and can indeed make matters worse.
Background
[1] Dr. Mae-Wan Ho, Mealy bug plagues Bt cotton in India and Pakistan, GM Watch 27.01.10
[2] ELUSIVE BENEFITS OF Bt - May 2011
SOURCES:
It seems that these Bt plants have a less robust epidermis (outer skin) and possibly more nutritious sap for the flies to feed on.
It's always been assumed that, since the Bt toxin is produced by plant tissues and isn't present in the sap, sap-feeding insects won't be exposed to it. However, it's been pointed out that, as the flies penetrate through to the GM plant tissue to reach the sap, they are exposed to low levels of the toxin. The stress of contact with sub-lethal amounts of a toxin are notorious for stimulating reproduction in insects.
Even more complicated is what's happening in Brazil's Bt cotton fields where the bollworms targeted by the GM toxin are becoming increasingly resistant.
Scientists there have discovered that the pests seem to be helped by the presence of a non-pathogenic virus. Virus-infected bollworms not only have increased resistance to the Bt insecticide, but mature faster and have enhanced reproduction.
There's evidence that the virus' action is to activate immune and developmental biochemical pathways in the bollworms.
OUR COMMENT
It seems subtle changes in the structure of GM plants can make them more susceptible to biotic stress, and the Bt toxin itself, in the wrong quantities, can promote pests.
Moreover, while virologists direct all their attention to pathogenic viruses, there's clearly a vast scope for unrecognised friendly viruses to be giving Nature a helping hand and GM plants a slap in the face.
Tell your food and farming regulators to ditch the simplistic notion that humanly-designed 'fixes' for complex problems in a complex environment will ever work as humanly intended, and can indeed make matters worse.
Background
[1] Dr. Mae-Wan Ho, Mealy bug plagues Bt cotton in India and Pakistan, GM Watch 27.01.10
[2] ELUSIVE BENEFITS OF Bt - May 2011
SOURCES:
·
How do genetically engineered crops speed up
the spread of plant pests? GM Watch
24.03.21
·
Mauricélia
F Almeida, et al., 2021, Plant Resistance in Some Modern Soybean
Varieties May favor Population Growth the Modify the Stylet Penetration of
Bemisia tabaci Hemiptera: Aleyrodidae), Journal of Economic Entomology
· Yutao Xiao, et al., 2021, Rapid spread of a symbiotic virus in a major crop pest following wide-scale adoption of Bt-cotton in China, Preprint 10.02.21
Image: Bt Cotton. From Creative Commons
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