The positive risk assessments of GM grain crops have been based on the premise that, because they are adapted for wind pollination and largely self-pollinating, there is little concern about gene-flow from them into other crops.
Grain crop have a flower structure which aids wind-pollination, and their pollen is not well adapted for carriage by insects. Tests have shown that the amounts of pollen carried by wind decrease exponentially with distance from the crop, reaching zero within a few meters. Also, pollen is short-lived. The risk of gene pollution arising from GM grain crops has, therefore, been considered effectively zero.
However, a recently published study has challenged this view.
Although insects are major pollinators of many fruit and vegetable crops, their presence in wind-pollinated plants has never been factored in. A team of Chinese and American scientists took a long hard look at insect activity in rice crops to see what impact it might have.
The study has several strands, all of which yielded quite surprising data.
A two-year nationwide survey in Chinese rice fields identified over 500 species of insects visiting the flowers. These included 40 species of bees and 28 species of hover-flies all of which collect large amounts of pollen.
Honeybees were the most abundant species found in 26% of locations. They therefore received a more detailed study. The bees came from colonies up to half a kilometer away from the field, appearing as soon as the flowers opened and continuing to forage there until the flowers withered. Individuals were found to be carrying 400 or more pollen grains by the end of each trip.
Investigation of one colony located 500 meters from the rice field indicated that 81% of the pollen arriving there was viable.
A field-cage experiment showed that gene flow from GM to conventional rice with or without the presence of bees was below 1%. However, the bees were responsible for a significant, up to 25-fold, increase in flow. In the big outdoors however, bees introduce a non-random effect into gene flow. Because they concentrate their attention to areas where flowers are at the optimum stage of maturity, the gene flow from their activity can result in pockets of “extremely large” (10%) levels of hybrid seed formation.
It was noted that other studies have recorded honeybees foraging over 13 kilometers from their hive, and have found that pollen grains can be further spread by nest-mate mixing.
This study highlights, once again, the level of assumption-based 'science' which routinely permeates the risk assessment of GM crops.
The question of GM pollen-contaminated honey is another very thorny one. A small study in Mexico, whose exports of honey to the EU alone were worth $54 million in 2011, found GM pollen in honey after the first year GM soya was planted there. This clearly contradicts industry claims that bees do not visit soya because the flowers are self-pollinated. Note that the Mexican courts have now cancelled Monsanto's permit to grow GM soya there.
Co-existence of GM rice, soya and similar grain crops with non-GM is clearly impossible unless flowering times can be guaranteed to be entirely separate in time. But then, what's a farmer expected to do if unusual weather alters his crop's flowering time? Plough it under? Annihilate all the insect pollinators in his field?
- De-qiang Pu, et al., 2014, Flower-visiting insects and their potential impact on transgene flow in rice, Journal of Applied Ecology
- Nina Lakhani, Sweet victory for Mexico beekeepers as Monsanto loses GM permit, www.theguardian.com Povertymatters Blog, 8.08.14