WEST LAFAYETTE, Ind. – For years, farmers and agribusinesses have talked about being on the pesticide treadmill: A few years after a pesticide is introduced, insects develop resistance to it. So another chemical is used – at least until the bugs overwhelm that one.
Then another chemical is used. Then another. Then another.
But Barry Pittendrigh, assistant professor of entomology at Purdue University, says it’s possible to stop the treadmill, or at least slow it to a crawl.
Alternating use. Pittendrigh and Patrick Gaffney, of the University of Wisconsin-Madison, have developed a method to use pesticides so that genetic resistance doesn’t arise.
The technique is called negative cross-resistance, and it involves using multiple pesticides in a precise way to stop the pests.
With the technique, scientists would identify a second biocide – pesticide, antibiotic, herbicide or fungicide – that specifically kills the resistant pest. Then the two biocides would be used together, either concurrently or alternated, to prevent resistance.
Buying time. The researchers say their model shows that negative cross-resistance biocides 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 said.
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 organisms,” Pittendrigh said. “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 biocide, such as an insecticide for a major pest or an important antibiotic, this method could have great value.”
Antibiotic resistance. Pittendrigh said, in theory, the method also should work to prevent antibiotic resistance in bacteria.
“This approach may also be useful in combating antibiotic resistance,” he said.
The method also could be used with herbicides or fungicides.
No pesticide is 100 percent effective against its target, and that’s where the problem of chemical resistance comes in. If a pesticide kills 98 out of 100 bugs, the only two left are both resistant to the chemical.
If those two mate, then all of their offspring also will be resistant. If the same thing happens in field after field, soon entire populations of the pest are immune to the effects of the pesticide.
The situation is worse with genetically modified crops. Because these plants deliver pesticide in such a direct and effective manner, they are even more susceptible to the rise of resistant insects.
Once a new compound has been identified as being effective on resistant pests, it can either be alternated with the original biocide, 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 said. “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 somebody tried to cut corners and didn’t use both compounds, the method wouldn’t work.”