Bedbugs: Have they Built a Resistance To Insecticides?

The insecticides you may be using to rid your bed of pests may not even begin to scratch the surface, according to a new study from Virginia Tech and New Mexico State University. In the latest study, researchers found an overuse of common chemicals has built up bedbugs' resistance, thus making them far less effective at shielding your sheets and mattresses than advertised. 

"While we all want a powerful tool to fight bed bug infestations, what we are using as a chemical intervention is not working as effectively it was designed and, in turn, people are spending a lot of money on products that aren't working," Troy Anderson, an assistant professor of entomology in the Virginia Tech College of Agriculture and Life Sciences, said in a news release.

Researchers looked at a class of insecticides known as neonicotinoids (also associated with bees), or neonics, which are often paired with pyrethroids in commercial applications to treat bedbugs.

"Companies need to be vigilant for hints of declining performance of products that contain neonicotinoids," Alvaro Romero, co-author and an assistant professor of entomology at New Mexico State University, added. "For example, bedbugs persisting on previously treated surfaces might be an indication of resistance."

Two groups of bedbugs were treated with neonicotinoids: One group was of bedbugs from homes in Cincinnati and Michigan that had previously been exposed to neonics and the other was a colony that had been kept isolated for the past 30 years in a lab run by Harold Harlan with the Armed Forced Pest Management Board. Researchers also examined a pyrethroid-resistant population from New Jersey that had not been exposed to neonics since they were collected in 2008.

While bedbugs from Harlan's lab died when exposed to a very small amount of the insecticide, the New Jersey bedbugs fared slightly better, showing moderate resistance to four different types of neonics, researchers say. 

However, those collected from Michigan and Cincinnati -- which were collected after combinations of insecticides were introduced to the U.S. -- had a much higher resistance to neonics. For instance, it only took 0.3 nanograms of a substance called acetamiprid to kill 50 percent of the non-resistant bedbugs from Harlan's lab, but it took more than 10,000 nanograms to kill 50 percent of the Michigan and Cincinnati bedbugs.

When testing another substance called imidacloprid, just 2.3 nanograms was enough to kill 50 percent of Harlan's bedbugs, but it took 1,064 nanograms to kill the Michigan bedbugs and 365 nanograms to kill the Cincinnati bedbugs. 

Researchers believe that neonicotinoid resistance in the New Jersey bedbugs, which were collected before the widespread use of neonics, could be due to pre-existing resistance mechanisms.

"Unfortunately, the insecticides we were hoping would help solve some of our bed bug problems are no longer as effective as they used to be, so we need to reevaluate some of our strategies for fighting them," added Anderson, who is also a researcher at the Fralin Life Science Institute.

When bedbugs are exposed to insecticides they produce "detoxifying enzymes" to counter them. It follows then New Jersey bedbugs -- who have learned the toxicity of certain chemicals -- produce more of these enzymes than bedbugs from the susceptible Harlan bedbugs, thus ensuring their survival. 

Their findings were recently published in the Journal of Medical Entomology. 

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