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Insect Resistance to Bt Crops can be Predicted, Monitored, and Managed
Since 1996, crop plants genetically
modified to produce bacterial proteins that are toxic to certain insects, yet
safe for people, have been planted on more than 200 million hectares worldwide.
The popularity of these Bt crops, named after the bacterium Bacillus
thuringiensis, comes from their ability to kill some major pests, allowing
farmers to save money and lessen environmental impacts by reducing insecticide
sprays.
However, since insects can evolve
resistance to toxins, strategies must be implemented to ensure that Bt
crops remain effective. A new study published in the December issue of
Journal of Economic Entomology entitled “Field-Evolved Insect Resistance to
Bt Crops: Definition, Theory, and Data” (http://www.entsoc.org/btcrops.pdf)
analyzes insect resistance data from five continents, as reported in 41 studies,
and concludes that existing theories and strategies can be used to predict,
monitor, and manage insect resistance to Bt crops.
According to lead author Dr. Bruce E.
Tabashnik, “Resistance is not something to be afraid of, but something that we
expect and can manage if we understand it. Dozens of studies monitoring how
pests have responded to Bt crops have created a treasure trove of data
showing that resistance has emerged in a few pest populations, but not in most
others. By systematically analyzing the extensive data, we can learn what
accelerates resistance and what delays it. With this knowledge, we can more
effectively predict and thwart pest resistance.”
Among the authors’ conclusions are:
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The refuge strategy
(growing non-Bt crops near the Bt crops) can slow the evolution of
insect resistance by increasing the chances of resistant insects mating with
non-resistant ones, resulting in non-resistant offspring.
·
Crops that are “pyramided”
to incorporate two or more Bt toxins are more effective at controlling
insect resistance when they are used independently from crops that contain only
one Bt toxin.
·
Resistance monitoring can
be especially effective when insects collected from the field include survivors
from Bt crops.
·
DNA screening can complement traditional methods for monitoring resistance, such
as exposing insects to toxins in the lab.
·
Despite a few documented
cases of field-evolved resistance to the Bt toxins in transgenic crops,
most insect pest populations are still susceptible.
With Bt crop acreage increasing
worldwide, incorporating enhanced understanding of observed patterns of
field-evolved resistance into future resistance management strategies can help
to minimize the drawbacks and maximize the benefits of current and future
generations of transgenic crops.
The full article is available at
http://www.entsoc.org/btcrops.pdf.
Bruce Tabashnik, the lead author can be contacted at
brucet@ag.arizona.edu or 520-621-1141.
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