GM-free Scotland

News | February '10 | Swapping diseases

Image of mealy bugsSo far, all GM crops commercialised are designed to resist pests. Can we really create a crop impervious to pests using a randomly-inserted concoction of foreign DNA without nature fighting back?

Cotton

Bt insecticidal GM cotton hybrids have come to cover 81% of India's cotton-growing land within five years of commercialisation. The crops have lived up to their promise of protecting against the American bollworm, and the number of sprays needed has dropping from 30 to less than 5.

However, cotton plants in India have some 165 natural pests, and in some areas attacks by other enemies, such as aphids and thrips, have been on the increase. Not only that, but previously unknown pests, such as tobacco leaf streak virus and tobacco caterpillars have emerged to add to the damage.

The worst of these novel problems has been the mealy bug. This sap-sucking insect can thrive on a wide range of wild and domestic plant types, so there's always something nearby it can live on until the next Bt cotton feast emerges. The bug can reduce cotton yields by 50%, and has forced many farmers to rip out their expensive GM cotton plants and replant with rice in a desperate bid to cut their losses.

Ironically, the species of mealy bug which is causing the devastation is thought likely to have been imported from America on Bt cotton seed; the native Indian mealy bug is controlled by natural predators and diseases, and is not a problem.

In US Bt cotton fields, the 'tarnished plant' bug is having a field-day. This pest has been around for as long as records have been kept. Because both larvae and adults feed on cotton plants, their damage extends throughout the growing season, and both feed preferentially on the plants' reproductive structures. They can,therefore, cause near-total crop loss. The reason the tarnished plant bug is so troublesome on Bt cotton is simply that the transgenic insecticide doesn't bother it, and the spraying which previously kept it under control along with a number of other serious insect pests, is no longer being carried out.

Besides its effects on insect pests, Bt cotton exudes its toxin into the soil. Add to this that the GM plants are super-efficient at extracting fertilizers from the soil. The net result of these is that soil quality is disturbed, possibly explaining the lower yields recorded in subsequent crops in the same field.

Squash

Virus-resistant GM squash, grown widely throughout the USA and much of Mexico, successfully resists zucchini yellow mosaic virus, a virus which leads to stunted growth and serious yield loss. The down-side of the novel squash is that it easily pollinates wild gourd, creating a reservoir of GM, virus-resistant plants in the environment. This wouldn't be a problem if squash didn't have other major pests.

Cucumber beetles are specialists herbivores on gourd varieties, where they create open wounds in the plants. The beetles also like to congregate on gourd leaves to mate. Add to this recipe, a bacterium which causes fatal 'bacterial wilt disease' is carried by cucumber beetles and is shed in their dung into the open wounds. Just to extend the problem to the wider environment, the bacteria falling near the nectaries of the gourd flowers can be picked up by foraging bees and spread to plants far and wide.

GM virus-resistant plants have no more resistance to the cucumber beetle nor to bacterial wilt disease than their wild relatives. The GM trait does, however, mean that they are taller and stronger than the stunted, non-GM, virus-infected gourds around, and so much more attractive to the cucumber beetles and all the sudden death they transmit.

Wild gourd, previously controlled by natural diseases such as mosaic viruses, is an important weed-pest in other crops. In its new, GM, form it acts as a fine perpetual refuge for cucumber beetle in between squash crops.

Soya, maize, cotton, caonla

Roundup Ready GM crops (soya, maize, cotton, canola ...) have been the most successful gene-technology venture worldwide. These plants are transformed to resist the weed-killer, glyphosate, so that the weed-pests growing up around the young crop plants can be controlled by spraying.

Glyphosate is actively absorbed by plants, but is not metabolised. The weedkiller, therefore, can accumulate in the roots of the Roundup Ready plants where it disrupts plant growth hormones reducing root growth, and disrupts plant defense compounds predisposing the plants to soil fungal pathogens.

The soil receives glyphosate not only directly from spraying, but from decomposing plant matter, and from root exudates. Once in the soil, some glyphosate dissolves in ground-water and is washed away, while some is degraded by soil bacteria. The rest remains to cause mischief: for example, some forms of microbial life are depressed by the glyphosate while others are stimulated.

The net result of all the above natural reactions is that increased fungal disease is seen in subsequent crops grown up to three years after a field has been treated with Roundup.

To crown it all, glyphosate forms a stable complex with essential soil micro-nutrients, such as manganese, iron, and possibly nickel. In this form, the minerals are no longer available to crops and yield is depressed.

OUR COMMENT

No doubt, the biotech industry's answer to these catastrophic environmental forces is to apply more of its artificial genes and more of its chemicals: cotton with genes to resist mealy bug, squash with genes to resist cucumber beetles and bacterial wilt disease, Roundup Ready plants with genes to resist fungal infection and to increase mineral uptake. As each new gene is stacked into the plant, the drain in the plants' resources from each new, forced, metabolic direction also stack up. The soil and wild environment will always present an infinite reservoir of benign life-form which can turn nasty the second a man-made weakness appears in its fabric.

The above account gives a number of causes for concern.

Possibly the most alarming is the finding that viruses previously associated only with other crops are appearing on GM cotton. One of the first and repeated warnings about the dangers of gene-technology was the use of viral promoters attached to the artificial genes to switch them on. Has the novel viral DNA, outside of its natural context in a GM plant, invited in other viral material?

The deployment of GM squash over such a huge area amongst wild plants which it can readily pollinate is simply irresponsible.

The massive use of Roundup Ready plants, which has clearly gone ahead without the appropriate studies of soil effects, is criminal.

Our only sustainable way forward in global agriculture is one which taps into the naturally balancing powers of nature, and is based on a wise combination of locally suitable crops. Since this route is not a profitable one for the biotech industry, a little naturally balancing pressure from those whose interests lie in a continuing supply of healthy food for themselves and their families, would not go amiss.

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