Another problem has arisen with the controversial class of insecticides known as neonicotinoids. Bed bugs are rapidly evolving resistance to them, suggesting these chemicals may soon lose their effectiveness, and hotel stays could become much scratchier operations.
Neonicotinoids, or neonics, were invented in the 1980s and have rapidly become the world's most widely used insecticides. They are less damaging to birds and mammals than other classes of insecticides, but they have been restricted in the European Union out of concern that agricultural use is harming beneficial insects such as honey bees.
Less attention has been paid to their use in killing household insects such as bed bugs, as mattresses seldom house beneficial insects. However, a study by Dr. Alvaro Romero of New Mexico State University raises a different concern.
In the Journal of Medical Entomology, Romero compared the response of bed bugs collected from Cincinnati and Michigan dwellings in 2012 with two populations that were collected some years ago and bred in a pesticide-free environment.
One historical collection was made by noted entomologist Dr. Harold Harlan 30 years ago, the other from Jersey City in 2008. The 30-year-old population died like flies when exposed to four different neonics. The Jersey bugs were as susceptible as Harlan's collection to two of the neonicotinoids, but showed signs of resistance to two others.
Resistance has accelerated dramatically since then. Both 2012 colonies required 30,000 times the dose of one neonic – acetamiprid – to kill 50 percent of the bugs in a sample compared to those from Harlan's colony. For imidacloprid, the world's most widely used neonic, the required dosage was more than 100 times higher for the Cincinnati bed bugs and 400 for those from Michigan, compared to Harlan's bugs.
The other two insecticides produced similar results, despite not having been used against bed bugs before 2012, possibly because resistance to one insecticide often provides some level of protection against similar chemicals.
Bed bug lifecycle. Crystal Eye Studio/Shutterstock
"Companies need to be vigilant for hints of declining performance of products that contain neonicotinoids," Romero said in a statement. "For example, bed bugs persisting on previously treated surfaces might be an indication of resistance. In these cases, laboratory confirmation of resistance is advised, and if resistance is detected, products with different modes of action need to be considered, along with the use of non-chemical methods."
Bed bugs were an unpleasant but common pest prior to the invention of broad-spectrum insecticides, including DDT. They became rare in wealthy countries in the 50s and 60s, before bouncing back as resistant survivors multiplied without competition. Romero's work suggests resistance appeared faster to neonics than to earlier generations of insecticides. The population collected in 2008 had been exposed to pyrethroid insecticides, but not neonicotinoids. Romero said that "Elevated levels of detoxifying enzymes induced by other classes of insecticides might affect the performance of newer insecticides."
Romero suggested that this possibility needs further investigation, as if it is true it will make insect control even more challenging.