As we explained a while back, resistance to various insecticides is threatening the peace of mind (what little they have) and comfort of New Yorkers because bedbugs were popping up in all sorts of places. But it's not just Gotham that's affected we may be on the verge of a national infestation because of the rise of the pests' resistance to commonly used chemicals. And a recent report suggests that may well be the case.
Drs. Alvaro Romero and Troy D. Anderson of New Mexico State University and Virginia Tech University, respectively, joined forces to investigate the extent to which bedbugs are becoming resistant to widely used insecticidal chemicals. These investigators discussed how bedbugs were well-controlled by DDT and other insecticides in the 1940s and '50s, but after about a decade of use the bugs started to develop resistance. And the same thing happened with another widely-used class of insecticides pyrethroids. So lately, exterminators have been forced to use neonicotinoids ("neonics"), a newer class of pesticide.
Drs. Romero and Anderson investigated the extent to which neonics were effective against bedbugs that were resistant to the older pyrethroids. In order to do so, they collected bedbugs from infested homes in Cincinnati, OH, Troy, MI and Jersey City, NJ, which were known to be resistant to pyrethroids. The Ohio and Michigan bedbugs were collected in 2012, and the NJ bugs had been maintained in a lab for five years (before neonics were used). These were compared to a control population of bugs that had been maintained in a lab for about 30 years, and thus were considered insecticide-naive.
Sixty bedbugs from each sample were each treated with one of four neonics by putting a drop of the chemical on the insects' backs. After 72 hours, the researchers found that the neonics killed fewer bedbugs in the Michigan and Ohio samples than in the sample from the long-term laboratory colony.
For example, while 10 nanograms of the neonic acetamiprid killed 100 percent of the bugs from the lab group, 1,000 times more of the same insecticide killed only some of the bedbugs from Ohio and Michigan.
The authors also measured the activities of several detoxifying enzymes and found that these were (as expected) higher in bedbugs from the pyrethroid-resistant Ohio and Michigan colonies as well as from the New Jersey sample. Thus, they concluded: "Our study is the first report of resistance in bedbugs to the neonicotinoids acetamiprid, imidacloprid, and thiomethoxam, active ingredients of various pyrethroid neonicotinoid combination products currently registered for bed bug control in the United States."
These results do not bode well for bedbug control, since apparently resistance to one class of insecticide (pyrethrins) can also confer resistance to another (neonics). Further research will obviously be needed to find pesticides that evade these common resistance pathways.