Each GMO must be treated independently from all others because its ecological effects will vary depending on the nature of the gene transferred and the method of pollination of the GM plant. Some pollinating insects do not travel far so pollen is unlikely to be transported any great distance, but honeybees commonly forage 5-6 miles, occasionally 10, and migratory insects or small ones which get carried by wind can also travel great distances. Pollen from wind-pollinated plants can travel very much further. Where the GMO involves an insecticide toxin gene then the precautionary principle should apply and some limit set to the distance pollen is 'permitted' to travel. For example, if say 100 pollen grains from maize are deposited on 10 sq cm of leaves 10 miles distant, this may be considered unacceptable.

Some GM pollen can introgress into wild relatives of cultivated plants and it is very important to be sure that the introduced genes do not persist in the wild. Current research results with oil-seed rape suggest that though introgression certainly occurs the genes do not persist more than a year or two, at least in the areas where this has been researched. However, similar experiments should be routinely carried out in different parts of the country before any GMO is released for widespread use. Once a common weed has become resistant to herbicides, and if that gene persists, then not only will the money spent on developing that particular GMO will have been wasted, but other crops may suffer due to competition from herbicide-resistant weeds.

The effect of GM pollen on organic farmers can be very serious because they cannot protect their crops from GM crops several miles distant. GM pollen can also adversely affect the environment, e.g. GM pollen from maize has been shown in the USA to kill monarch caterpillars that eat leaves dusted with GM pollen containing insecticidal toxins.

I believe the precautionary principle should apply: unless a particular GMO is seen to have substantial 'benefits', then it should not be authorised for release, even if it appears to have no harmful medical or health effects. By 'benefits' I mean benefit not just to the manufacturer and the farmer, but also to the consumer, and the environment, and it should not do harm to neighbouring landowners (who may, for example, be trying to farm organically).

Malcolm Edmunds, Professor of Zoology
Department of Environmental Management
University of Central Lancashire