It is not known how GM technologies will impact upon biodiversity. The CBD defines biodiversity as:

“The variability among living organisms from all sources including, inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.”

The introduction of a transgene into a recipient organism is not a precisely controlled process and can result in a variety of outcomes with regard to integration, expression and stability of the transgene in the host (FAO and WHO 2003). The risks associated with modifying the genetic structure of crops are not well understood and there is little agreement on either the severity or likelihood of potential risks. This controversy emanates from a scientific dispute about how “stable” GM crops are. Several concerns can be identified.

Figure 5: Biodiversity in mountain regions First, GM technology could result in the contamination of crops through gene transfer – “genetic pollution” – and the development of “super weeds” (Altieri 2002, Porter 2005) and therefore have a negative impact on biodiversity. A further concern about GM crops is that the genes could “escape” and, through cross-pollination, mix with non-GM crops or their weedy relatives. For example, an herbicide-tolerant gene could be transferred to weeds in wild habitats, turning them into “super weeds” (ERA 2005). There is evidence of the unintentional spread of genes from GM crops (Monroe 2004).

Second, transgenic crops modified to be resistant to a particular pest or disease may have a negative effect on non-target species that are harmless or beneficial. For example, Bt maize pollen may be toxic to the Monarch butterfly (Losey and others 1999). Although the Monarch butterfly is native to Mexico, the United States of America and Canada (Manos-Jones 2004) it is possible that other butterfly species in Africa can be similarly affected. On the other hand, the alternative to transgenic crops could be as harmful to the environment. For instance, the practice of routine spraying of broad-spectrum insecticides is non-selective, and therefore kills all insects regardless of whether they are beneficial or harmful to the crop (Ives and others 2001). A British study on oilseed has recently concluded that it is not the GM crops that harm wildlife but the herbicides sprayed on the crops that significantly reduce the broad leaf weeds such as chickweed, a major bird food (Brown and Gow 2005). The magnitude of these GMO risks to non-target organisms, including beneficial insects, is largely unknown as there have been no comprehensive studies in Africa to date.

Third, pest resistance can occur with frequent use of any pest control product (Soil Association 2003b). Insects can develop resistance to toxins such as the Bt bacterium, reducing the effectiveness of this control method. In Australia, India and China, for example, pests are becoming resistant to some GM cotton crops that have Bt genes inserted (Spinney 1999). Research into the safety of GM crops using genes that produce toxins should precede commercialization and not follow it. Inbred pest resistance might also be toxic to people in the long term. For example, long-term consumption of peas, Lathyrus sativus, can cause paralysis if a toxin in the peas accumulates in people, as has happened in Bangladesh and India (Messons cited by Sawahel 2005). Bt crops have proven to be unstable and ineffective; some insects, which survive Bt, transmit genetic resistance to their immediate offspring. If Bt becomes ineffective as an implanted pest control strategy within one insect generation, then organic farmers will be robbed of a valuable biopesticide. Regional cases of Bt resistance have already been reported (Spinney 1999). Insects resistant to the genetically modified Ingard Bt cotton were reported in Australia (Australian Broadcasting Corporation 2001). Indeed, GM plants are not behaving as intended: in 1996, Monsanto’s pest-resistant Bt cotton succumbed to a heat wave in the southern US and was destroyed by bollworms and other pests (Spinney 1999). In 1997, farmers who grew Monsanto’s herbicide-tolerant cotton saw the cotton balls fall off their crops (Spinney 1999).

Fourth, GM crops engineered to be resistant to specific herbicides enable farmers to spray weeds without damaging crops (Soil Association 2003a). Weeds are developing resistance to these herbicides, and rogue GM plants that grow after a harvest (volunteers) have appeared and spread widely (Altieri 2002, ERA 2005). In particular, GM oilseed rape volunteers have spread quickly, and some plants have become resistant to several herbicides through cross-pollination (Brown and Gow 2005). Elsewhere, GM cotton crops have failed to impart protection from pests resulting in increased use of chemical sprays: farmers are making more frequent applications and reverting to older and more toxic chemicals (Soil Association 2003b).

Fifth, GMOs could impact on genetic diversity. The increased competitiveness of GMOs could cause it to damage biologically-rich ecosystems. Transgenic crops could encourage biodiversity loss through the establishment of monoculture agriculture which replaces traditional crops and other established varieties (Altieri 2002). Currently, the main potential cause of loss of biodiversity is agricultural expansion, which destroys habitats. The needs of a growing global population have largely been met by bringing more land into agricultural production (Ives and others 2001). Proponents of GM crops highlight this and suggest that transgenic crops may be able to help preserve uncultivated habitats by increasing yields on land already under cultivation (Ives and others 2001), reducing the need for conversion.

Sixth, ecological and health hazards are also posed by genetic use restriction technologies (GURT) which are commonly known as terminator technology (Mclean 2005). These organisms do not flower and fruit and therefore provide no food for the multitude of insects, birds and mammals that feed on pollen, nectar, seed and fruit, and will inevitably have huge impacts on biodiversity (Mclean 2005). Sterile trees can still spread by asexual means and the genes can spread horizontally to soil bacteria, fungi and other organisms in the extensive root system of the trees, with unpredictable impacts on the soil biota and fertility. As transgenic traits tend to be unstable, they could break down and revert to flower-development, spreading transgenes to native trees, or creating pollen that poisons bees and other pollinators as well as causing potential harm to human beings (ISIS 2005b). The sterile monocultures are much more likely to succumb to disease, which could potentially wipe out entire plantations (Spinney 1999). Some companies have developed GM crop seeds that use GURT. As a result, farmers become dependent on large corporations and must purchase new seeds every season (ERA 2005). In addition to social equity issues associated with these monopolistic tendencies, GURT may have environmental risks and thus the technologies require further evaluation. GM crops can be unstable (Hansen 2000, GMWatch 2005) posing risks to other plants.

There are counter claims to all these concerns: the use of herbicide-resistant and pest-resistant crops is believed to have positive implications for biodiversity. With non-herbicide tolerant (non-transgenic) soybean, farmers must clear the weeds before planting their seeds. With herbicide-tolerant soybean, however, the weeds can be better controlled; farmers can plant the seeds by sowing them directly in relatively undisturbed soil. This conserves moisture and soil fauna and flora and also reduces water and wind erosion (Ives and others 2001).