About 80% of the corn and cotton planted in North America is genetically engineered
to resist pest insects.
These are commonly called Bt crops and
produce proteins that target very specific pests.
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The process of genetic engineering is faster and more precise than traditional
breeding methods alone, allowing the modification or
insertion of specific genes without altering any other traits.
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Bt crops were created by using genes from Bacillus thuringiensis, or Bt,
which is a common soil bacterium that produces proteins that are toxic to
some species of pest insects.
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The genes that produce these proteins were inserted into the DNA of the crop.
As a result, the Bt crop produces these proteins and
defends itself against specific pests.
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When a pest feeds on the Bt plant, the protein
binds to receptors in the insect's gut, causing the gut wall to break down and
rupture, leading to the death of the insect.
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These proteins must bind to specific receptors in the pest's gut to work.
Other organisms such as humans, other mammals, beneficial insects and
spiders don't have those receptors and are unaffected.
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Although, Bt crops have helped managed pests for over 20 years,
they are losing their effectiveness against some pests.
Here are a couple of reasons why.
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First, while the goal of Bt crops is the kill the target insects that feed on them.
This is not always achieved due to natural variability to the levels of Bt
protein within a plant.
This means that some tissues in a plant may not have lethal levels of the protein.
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Second, insect populations are also variable.
By chance, some insects are naturally less susceptible to certain Bt proteins.
They will survive and reproduce, while the majority of the population dies.
This is how resistance develops, and resistance can always develop with
any long term pest management approach, including Bt crops.
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However, farmers can slow down resistance with an integrated pest management
strategy, or IPM.
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It's a long term approach that uses multiple pest management tools.
As a result,
no single approach to managing pests should ever be seen as a standalone tool.
But instead, should be part of a larger strategy.
Let's take a look at some tools that could be used with Bt
crops to make them more effective and long lasting.
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It all begins with scouting.
The only way to know what pests are in the field and
how much damage they have caused is by walking out into your field and looking.
Once you have accurate information about your pest problem,
then you can develop a plan of attack.
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The second tool is crop rotation.
Avoid planting Bt crops in the same field two years in a row.
You could use non Bt varieties of the same crop or
better yet grow a different crop entirely in the alternating years.
Either way this gives the insects less exposure to Bt proteins thereby
slowing their resistance to it.
If a field has low pest populations, you could avoid using Bt crops until your
scouting indicates that pests are becoming a significant problem.
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Insecticides can be used in place of Bt crops to manage many pests.
Insects can also develop resistance to insecticides and they too
should be rotated and used only as part of a larger pest management strategy.
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The final tool is refuge planting this is mandatory and
involves planting part of each field with a non-Bt hybrid of the same crop.
Some bags of Bt seeds have non-Bt seeds mixed in to create refuges.
This allows some non-resistance insects to survive and mate with any resistant
insects in the vicinity and producing non-resistant offspring.
However, you may need to create a separate refuge depending on your location.
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Remember, none of these tools should be used in isolation,
and every tool requires vigilance, including Bt crops.
Resistance is inevitable, you always need to pay attention to pest activity.
The only way these problems will be discovered is if someone is in the field
looking for them.
Look for unexpected plant damage and
an increase in the number of pests based on your past experience.
If so, it's time to get other professionals involved
to determine the nature and extent of the problem.
Your extension educator and
local seed sales representative
will be able to help.
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