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An Electron Micrograph of a bloodsucking bedbug.

A color-enhanced scanning electron micrograph of a bedbug.

Photograph by Tim Flach, Getty Images

Ker Than

for National Geographic News

Published March 14, 2013

Bedbugs are a growing public health issue in the United States and around the world, but their resurgence in recent years may have been aided by humans who unwittingly helped the pests evolve numerous ways of thwarting a common insecticide, scientists say.

In a new study published online today in Scientific Reports, researchers examined the genes of bedbugs from different U.S. cities and found that several of the populations had multiple means of resisting a class of insecticides called pyrethroids.

Pyrethroid insecticides are commonly used in bedbug control because of their relative safety for humans and pets, effectiveness, and low cost, but their use has also led to widespread development of resistance in the pests. (Learn about bedbugs and how to tell if you have them.)

To investigate how some bedbugs were defending themselves, scientists compared the genes of 20 pyrethroid-resistant populations of the insects from around the country against a susceptible colony from Los Angeles, California.

The team identified 14 genes that coded for proteins that were expressed at higher levels in the resistant insects, compared with the nonresistant Los Angeles population.

Insecticide Armor

Further investigation revealed that all of these "overexpressed" genes were active in the tough outer shell of resistant bedbugs, and either helped neutralize pyrethroid insecticides before they could take effect or prevented them from entering the insects' bodies in the first place.

"Many mechanisms of resistance seem to be in play in these various populations simultaneously," said study co-author Kenneth Haynes, an entomologist at the University of Kentucky.

The study also revealed that despite sometimes being separated by hundreds of miles, resistant bedbug colonies utilized many of the same genes to protect themselves against pyrethroid insecticides.

Bedbugs by themselves aren't very mobile, but Haynes suspects the bugs are catching rides with humans—or rather, their furniture.

"The transcontinental transport of furniture is likely a major source of [bedbug] movement," he said.

Long-Distance Relations

Human involvement would also explain another puzzling pattern, recently discovered by scientists at North Carolina State University, in which bedbugs from different cities were sometimes more closely related to one another than to other populations from the same city.

"We see isolated pockets where bedbugs across town may not be closely related to each other, but populations in [North Carolina] might be closely related to one out of Michigan," Haynes said, indicating that the bedbugs hitched a ride with a human moving to another part of the country.

Haynes cautioned that his idea is "highly speculative" and still unproven, but entomologist Zachary Adelman of Virginia Tech said the hypothesis makes sense.

"If local populations evolved their own [insecticide resistance] strategy and then mixed [with other populations], the result would be quite similar to what we see now," said Adelman, who was not involved in the study.

An intriguing question raised by the new findings, researchers say, is just when did bedbugs evolve their resistance?

"[Was it] in the past ten years? The past 50? Or are we looking at the past several hundred years or more?" Adelman said.

Figuring out the resistance time line, Adelman added, could provide insights about how fast evolution is working in bedbugs and could have implications for the future of bedbug control.

A New Prescription

Changlu Wang, an entomologist at Rutgers University in New Jersey, said the new findings are already providing valuable clues about how to better handle bedbugs.

For example, knowing that the cuticle, or protective outer layer, plays a key role in insecticide resistance in bedbugs "implies that better formulations can be designed to penetrate the cuticle more effectively and thus provide better control," said Wang, who was not involved in the research.

Study co-author Haynes said the findings also suggested that rotating different insecticides or targeting specific bedbug populations with a more "prescription-like" use of insecticides could be effective.

5 comments
Craig Dillon
Craig Dillon

Don't want bedbugs? Simple - don't use pesticides. Centipedes will then live, and will eat them. 

When pesticides are used, the prey species (cockroaches, bedbugs, etc.) absorb the pesticide and become toxic to their predators (centipedes, spiders, etc). A population boom in the prey species results. So, DON'T USE PESTICIDES. 

PS. Centipedes are secretive by nature, so if you see one, that means you have a nice protecting population of them. It doesn't matter if you squish the ones you see. 

PU Annie
PU Annie

The genes ofpyrethroid-resistant could have already existed in bedburgs, they just have been selected by incicticide. So,creatures have their own ways to survive, we can never kill all of them. All we could do is to control the amount of them in a low level, which can not harm the human.

Robert Sullivan
Robert Sullivan

@Craig Dillon That is just about the stupidest thing I have ever heard. After 30 years in the Pest control Industry I have never seen a centipede in a bed feeding on bed bugs. If not for pesticides we would be over run by many many pests and disease would run havoc. Hugging trees and eating nuts and berries is just fine. But please become just a little bit informed before offering an opinion.

Abraham Stone
Abraham Stone

@PU Annie  NONSENSE!!.Some, like roaches and flies, are completely detrimental to human beings and have no any positive impacts 4 us. their food lines are so simple.  so we should eliminate them, which will do no harm to nature.Dispite of the fact that eradicating them is quite impossible, we need to have a go!@! And the so called natural selection and survial of the fittest are just some kinds of kidding. Like the old saying:an ounce prevention is worth a pound of cure.

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