The Genetics Controversy - Agri-culture: Reconnecting People, Land and Nature - page 135

Direct and indirect effects of novel toxins
The fourth risk centres on the potential direct and indirect effects of novel
toxins expressed by genetically modified organisms. B.t. is expressed by all
cells in a B.t. maize or cotton plant, and therefore could affect either
beneficial organisms coming into direct contact with the plant or plant
products, or, indirectly, through consumption of a herbivorous insect that
has sequestered the toxin in its tissue. In laboratory conditions, several
potential risks have been demonstrated, such as genetically modified
potatoes that express a lectin; B.t. maize that affects ladybirds, lacewings
and butterflies; and B.t. products in the soil. However, these laboratory
studies do not necessarily mean that a real risk arises in the field. 14
A good example of the difficulties encountered is represented by recent
studies of the effect of pollen from genetically modified maize on
monarch butterflies ( Danaus plexippus ). The larvae of monarchs were reared
in laboratories on milkweed leaves dusted with B.t. maize pollen, and these
larvae ate less, grew more slowly and had higher mortality than those reared
on leaves dusted with non-genetically modified pollen. The potential
threat to a nationally important species raised great concerns about genet-
ically modified organisms in general, despite the fact that B.t. is already
known to be toxic to Lepidoptera. However, the dose of pollen required
to cause an effect in the field, the amount of pollen on milkweed leaves,
the likelihood of butterflies being exposed to pollen, and the photo-
degradation of B.t. and rain-washing effects all remain unknown. For
monarchs, timing is vital. In order for harm to occur, the larvae have to
emerge at the same time as maize is pollinating, a narrow period of seven
to ten days. However, monarch migration and B.t. pollen show only
coincide in certain areas; pollen does not travel far (90 per cent falls in
the first 5 metres); larvae on milkweed are not adversely affected by B.t.
pollen; and most milkweed tends not to be found close to maize fields.
Moreover, only one form of B.t. has been found to be consistently toxic
to monarchs. Again, this does not mean that all potential risks from B.t.
crops will be small, or even that all insects will not be harmed - just that
a detailed understanding of the context of the cropped environment is
needed before a clear judgement about risk can be made. 15
Changes to farm practices leading to changes
in biodiversity
As a result of the incorporation of genetically modified organisms within
their farm practices, farmers may also contribute directly or indirectly to