GMO Myths and Truths

management plans in place, sole reliance on Bt
crops for management of agriculture pests will likely
hasten the evolution of resistance in some cases.” 46
Also, the effectiveness of refuges relies on the
Bt crops expressing doses of Bt toxin that are
high enough to kill pests, and the non-Bt refuges
remaining free from Bt toxin-expressing genes. But
cross-pollination between GM Bt maize has been
found to cause “low to moderate” Bt toxin levels in
the refuge plants, 49 making refuges less effective.
5.4.3. Secondary pests attack Bt crops
Nature abhors a vacuum. So even when Bt toxin
succeeds in controlling a primary pest, secondary
pests move into the ecological niche. For instance,
in the United States, the Western bean cutworm
has increased significantly in Bt maize fields. 50 In
China and India, Bt cotton was initially effective
in suppressing the target pest, the boll weevil.
But secondary pests that are resistant to Bt toxin,
especially mirids and mealy bugs, soon took its
place. 51,52,53,54,55,56
Two studies from China on GM Bt insecticidal
cotton show that GM Bt technology is already
failing under the onslaught of secondary pests:
A study of 1,000 farm households in five
provinces found that farmers noticed a substantial
increase in secondary pests after the introduction
of Bt cotton. The researchers found that the initial
reduction in pesticide use in Bt cotton cultivars
was “significantly lower than that reported in
research elsewhere” and that “more pesticide
sprayings are needed over time to control
emerging secondary pests” such as aphids, spider
mites, and lygus bugs. In addition, a quarter of
the farmers thought Bt cotton yielded less than
non-GM varieties. Close to 60% said that overall
production costs had not decreased, due to the
higher price of Bt cotton seed. 57
Field trials conducted over ten years in northern
China show that mirid bugs have increased in cotton
and multiple other crops, in proportion to a regional
increase in Bt cotton adoption. The researchers’
analyses show that “Bt cotton has become a source
of mirid bugs and that their population increases
are related to drops in [chemical] insecticide use in
this crop.” Moreover, mirid bug infestation of other
food crops (Chinese dates, grapes, apples, peaches,
and pears) increased in proportion to the regional
planting area of Bt cotton. 58
It is clear from these developments that GM Bt
technology is not a “silver bullet” solution but is
economically and environmentally unsustainable,
as farmers who have paid premiums for Bt
insecticidal seed have had to return to spraying
costly and toxic pesticides.
5.4.4. Bt cotton farmers don’t always
give up insecticides
GM proponents often assume that farmers who
adopt Bt crops give up chemical insecticides –
but this is not necessarily the case. Tabashnik
(2008) reported that while bollworms have
evolved resistance to Bt toxin in one type of
GM cotton, this has not caused widespread crop
failure because “insecticides have been used
from the outset” to control the pest. 45 So claims
of reductions in insecticide use from Bt crop
adoption are unreliable unless there is evidence
that the farmer does not use chemical insecticides.
Moreover, most Bt crops currently commercialised
or in the pipeline have added herbicide tolerance
traits and so are likely to be grown with herbicides. 59
It is with good reason that one independent scientist
Pesticide use number-crunching
The most optimistic claim for reduced pesticide use from GM crops, in a paper by the private
consultancy firm to the GM industry, P G Economics, and based on “farm-level impact data” from an
unnamed source, is 6.9%. 41
In 2008 in the US, according to official government data, GM crop acres required over 26% more
pounds of pesticides per acre than acres planted to conventional varieties. 9
A 2011 study by French government scientists found that pesticide use could be reduced by 30%
without impairing yields or farm income 42 – and without GM crops.
GMO Myths and Truths 78