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Winter 2002
Jumping off the pesticide treadmill
By Steve Tally
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| Barry
Pittendrigh, assistant professor of entomology, is among the
researchers who have developed a method to reduce pesticide
resistance in insects. (Photo by Tom Campbell) |
Pittendrigh
and colleagues have developed a method that uses a little- known
biological phenomenon called negative cross-resistance (NCR) to
prevent chemical resistance from arising.
"The
idea applies not only to insect pests, but to any organism that
can be resistant to a chemical, whether it be weeds, bacteria, fungal
diseases or whatever," Murdock says.
With the
technique, scientists would identify a second compound--pesticide,
antibiotic, herbicide or fungicide--that specifically kills the
resistant pest. Then the two compounds would be used together, either
at the same time or alternated, to prevent resistance.
Previous
attempts to find compounds that would have a negative cross-resistance
effect haven't worked because they focused on too few compounds--fewer
than several dozen compounds, Pittendrigh says. However, Pittendrigh
says it is necessary to screen upward of 100,000 compounds to develop
a negative cross-resistance system. Pittendrigh and Gaffney have
invented a method to conduct these screens.
"We
outline how companies or individuals can search for and develop
NCR compounds to a commercially applicable level. We have already
done this using insects in the laboratory," Pittendrigh says.
"We are currently investigating the development of negative
cross-resistant toxins for use in field applications."
Scientists
are able to create resistant insects in the laboratory by using
a process known as EMS (ethylmethyl-sulfanate) mutagenesis. Using
the compound, scientists can produce insects with great genetic
variability and screen for those that are resistant to the insecticide
being tested.
"With
EMS mutagenesis you can actually create resistance in the laboratory
that is similar to that in the field," Pittendrigh says. "As
a general rule, this mimics nature, but at a much faster rate."
Once a new
compound has been identified as being effective on resistant pests,
it can either be alternated with the original compound, or they
can be paired together.
"My
own bias is to use two compounds at once, because, at the end of
the day, it's the simplest method," Pittendrigh says. "Farmers
could spray with the original pesticide for five years, and then
in the sixth year everybody would have to use both pesticides. But
if at that point somebody tried to cut corners and didn't use both
compounds, the method wouldn't work, and resistance would develop.
That's why my bias is to use two compounds concurrently because
it's the easiest to manage."
Although
using two pesticides is obviously more expensive than using just
one, Pittendrigh says genetically modified crops lower this hurdle.
"With
traditional agriculture, there are concerns about the costs of delivering
two different pesticides at once," Pittendrigh says. "But
with genetically modified crops, it's much easier and much more
cost effective to deliver two pesticides."
The researchers
say their model shows that using negative cross-resistant compounds
could delay resistance for decades, or even more than 100 years
in some situations.
"Although
negative cross-resistance is not the answer to dealing with resistance
to pesticides, it certainly has the potential to play a significant
role in dramatically slowing the rate at which resistance enters
insect populations," Pittendrigh says.
The result,
the researchers say, would be reduced costs, both financial and
social. "Nature will always find a way to get around whatever
we do to control pest or disease organisms," Pittendrigh says.
"But in some cases, this method may buy us years of usefulness
for compounds that are on the market. It costs a large amount of
money to bring a pesticide to market. If it's a highly important
compound, such as an insecticide for a major pest or an important
antibiotic, this method could have great value."
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