One of humankind's most intimate blood-sucking roommates, the bed bug, is notoriously resistant to the pesticides used against it. Now researchers have pinpointed the genes responsible for this resistance. The finding highlights how ineffective our current chemical arsenal has become, and could help researchers design pesticides better able to destroy the pests.

In the past 15 years bed bug infestations have spiked in the U.S., perhaps due to increased travel. Once the insect hitchhikers enter a new area, they spread readily: A single fertilized female can infest an entire apartment building. Getting rid of bed bugs can be expensive, time-consuming and tricky. Their paper-thin bodies let the bugs squeeze into cracks in furniture and walls, which are difficult to spray effectively.

To find clues that uncover how bed bugs are able to survive pesticides, a team of researchers from the University of Kentucky first sequenced the genes that were active in 21 pesticide-resistant bed bug populations obtained from infestations. By comparing the active genes in the field bed bugs with a susceptible lab-bred population's active genes, they identified 14 genes in the collected DNA having variants associated with pesticide resistance. Different populations carried different combinations of the gene variants. The team reported on March 14 in Scientific Reports they found as well that each of the bed bug populations tested carried at least two resistance variants. (Scientific American and Scientific Reports are both part of Nature Publishing Group.)

All of the genes identified were active (gave rise to specific proteins) primarily in the outer epidermis—an insect's tough, fingernail-like cuticle—rather than the digestive tract, which is where most insects develop mechanisms of pesticide resistance, says Subba Reddy Palli, a professor of entomology and one of the researchers involved in the new study. That finding made sense, given that bed bugs, which eat only blood, are exposed to pesticides solely by contact with their exoskeleton, which now appears to be chock full of protective genes.

Next, the team demonstrated that the genes they had identified caused resistance. They hobbled the genes by injecting young bugs with special RNA fragments designed to specifically silence the resistance genes. When the treated bugs were exposed the pesticides, they were susceptible. (The technique does not alter germ line genes, however, so the next generation would still be pesticide-resistant.) "A few other papers found similar genes," Palli says. "But no one had done the functional study yet—the gene silencing."

The high number of resistance genes in all populations examined by Palli and his colleagues is "horrifying," says Rajeev Vaidyanathan, an associate director of vector biology in the Center for Immunology and Infectious Disease at SRI International, who was not involved in the study. That the bugs have multiple ways of undermining the effects of pesticides is “devastating,” he adds.

The Kentucky researchers' bed bug genomic studies and those of a few other groups are "absolutely critical" for understanding the molecular basis for pesticide resistance, Vaidyanathan says. "This is step one. Step two is identifying novel targets for pesticides."

Two of the mechanisms suggested by the genetic findings were already flagged as contributors to bed bugs' pesticide resistance, Vaidyanathan says. One involves the metabolic enzyme cytochrome p450, which helps to break down toxins. (Humans have the same molecule.) A gene variant that confers resistance enables the bed bug to produce large quantities of the enzyme. The other mechanism relies on a protein found on the surface of nerve cells—an ion channel that tells the cell when to fire. Commonly used insecticides target that ion channel and cause nerves to fire continuously, paralyzing and quickly killing the insect. The resistant bed bugs often carry a mutation in the ion channel that prevents the pesticide from binding.

5 Comments

1. 1. Happy Hal 02:39 PM 3/15/13

   I still maintain, that live steam, is the best eradicator of Bed Bugs, and is ever so much better for the environment.

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2. 2. AnchovyRancher 02:56 PM 3/15/13

   Take a large vessel, say, a 1 gallon pickle jar and add a an ounce of tobacco to a full jar of water. Let it "brew" in sunshine (or near a heat source) for a day and strain. Put the concoction into a spray bottle and go to war with the bugs. It will stain white cloth, etc., so be careful about your placement of the spray. Bedbugs don't like tobacco so, "smoke 'em if you got 'em!" Yes, I smoke tobacco. No, I don't have bugs in my house.

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3. 3. northernguy 12:27 AM 3/16/13

   I have read that bedbugs are intolerant of high heat. It seems like it might be cumbersome but enclosing a building in plastic sheeting or whatever and raising the interior temperature is a better approach than spraying ineffective, toxic chemicals all over.

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4. 4. lmagadini 11:23 PM 3/19/13

   Hal and northernguy are right. I bought a house at auction and it was completely infested with bedbugs. I had 100% success getting rid of all of them by renting a propane heat cannon (like they use on construction sites) and raised the heat in the house to 150º (the propane tank was outside). I kept the heat in the house at that temp for 2 hours and it killed all the bugs and the eggs too. The whole thing cost me $30 for the day rental on the heat cannon. The pesticides don't work and don't fall for any of those gimmicks like bug-sniffing beagles - dumb! Just get the heat up -even if its room by room.
   If you have furnishings, remove whatever would melt (i.e. candles) or is easily flammable (i.e. spray cans). Throw away the mattress & box if they are heavily infested, or if you live in a hot climate, you can bag them and put them in the sun. Otherwise leave all the furnishings right where they are and heat the whole house up. Kills everything (spiders too!). If you see bugs DON'T squish them! That spreads the eggs. You can spray them with 90% rubbing alcohol and that dries them up.
   I hope people use this advice rather than buying useless pesticides or paying thousands for stupid services.

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5. 5. northernguy in reply to lmagadini 10:42 AM 3/20/13

   4. lmagadini 11:23 PM 3/19/13
   
   Thank You for your response.
   
   We have a bedbug infestation taking place in our downtown residential area. The progress of the pests can actually be mapped out as they move farther into the denser areas.
   
   So far the response has been mostly ineffective and costly chemical attacks. It's hard to believe that these chemicals don't pose at least some risk of toxicity to residents. They certainly are an inconvenience as people are required to vacate the premises for an extended period only to have the bugs return later.
   
   I have known for some time that both the bugs and their eggs are heat susceptible. Since such remediation isn't being employed I thought there must be some constraining factor that I was unaware of like maybe it takes weeks to work or whatever.
   
   Anyway thanks for showing me that it is relatively simple to implement in comparison to current procedures.

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