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The U.S. is fighting a battle it is not winning - a battle against bedbugs. One reason is that the bugs are evolving to survive common pesticides.

NPR's Jon Hamilton reports on a new study that uses genetics to help explain why some bedbugs just won't die.

JON HAMILTON: The pesticide known as DDT pretty much wiped out bedbugs more than 50 years ago. But they're back. And Susan Jones of Ohio State University in Columbus says the challenge has never been greater.

Dr. SUSAN JONES (Urban Entomologist, Ohio State University): We're dealing with a different bug than what we were decades ago when bedbugs were a problem in the U.S.

HAMILTON: Jones says the modern bedbug is harder to exterminate. To figure out why, she and other scientists compared the genes of today's bedbugs with those of earlier bugs. Jones says that's possible because, decades ago, a military bug expert started a colony of bedbugs that has lived in complete isolation ever since.

Dr. JONES: So it has had absolutely no exposure to insecticides. When you expose it to pesticides, the bugs just keel over.

HAMILTON: Jones says she got her modern bugs from an apartment complex in Columbus.

Dr. JONES: They had had a ongoing problem with bedbugs, repeated insecticide treatments, and the bedbugs were not going away.

HAMILTON: Suggesting they had developed resistance. So the researchers compared these new bugs with ones from the old colony. Omprakash Mittapalli from Ohio State University in Wooster says they focused on the genes involved in getting rid of toxins such as insecticides.

Dr. OMPRAKASH MITTAPALLI (Entomologist, Ohio State University): When an organism encounters a toxin, it basically breaks it down. It basically modifies the compound so that it's easily excretable.

HAMILTON: Mittapalli suspected modern bedbugs had genes that encouraged their bodies to produce more of the enzymes that break down pesticides. And he says that's just what they found.

Dr. MITTAPALLI: These enzymes are indeed higher in the pesticide-exposed populations compared to the pesticide-susceptible population.

HAMILTON: Breaking down toxins is just one way bedbugs have evolved to survive the exterminator's nozzle. They've also come up with strategies to protect cells from specific poisons.

Ken Haynes of the University of Kentucky has studied many populations of modern bedbugs exposed to common pesticides known as pyrethroids.

Dr. KEN HAYNES (Entomologist, University of Kentucky): Many of those populations have a level of resistance that's quite extraordinary.

HAMILTON: They can survive 1,000 times the amount of pyrethroid needed to kill a strain without any resistance. Haynes says all this new information suggests it may be time to try a different approach to killing bedbugs.

Dr. HAYNES: Instead of relying on the same insecticide generation after generation of the bedbugs, you'd rotate to a different class of pyrethroid or a different class of insecticide altogether with a different mode of action.

HAMILTON: And he says it's a good idea to include non-chemical approaches like steam. The new research appears in the journal Public Library of Science ONE.

Jon Hamilton, NPR News.

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