Bed bugs are developing resistance to two common insecticides, according to a new study in the Journal of Economic Entomology. Experts warn that many infestations can no longer be defeated with chemicals alone.
The common bed bug, Cimex lectularius, has previously shown considerable resistance to several other insecticides, including a commonly used one called deltamethrin. The reduced effectiveness of these chemicals is considered a main cause of the bed bug’s resurgence over the last decade, especially in big cities.
To find out if bed bugs were also developing resistances to two other common insecticides, bifenthrin and chlorfenapyr, Purdue University researchers gathered 10 different bed bug populations from Indiana, New Jersey, Ohio, Tennessee, Virginia and Washington, DC, and exposed them to the chemicals for seven days.
In five of these populations, they found reduced susceptibility to bifenthrin—meaning that more than 25% of the bed bugs survived. Three populations also had reduced susceptibility to chlorfenapyr.
Concerns about insecticide resistance aren’t new, says lead author Ameya Gondhalekar, research assistant professor at Purdue's Center for Urban and Industrial Pest Management. “The longer you use any product for the control of a particular pest, the more resistance issues you are going to have,” he says. In 2015, a University of Kentucky survey found that 68% of pest management professionals considered bed bugs the most difficult pest to control.
Bifenthrin, like deltamethrin, is a pyrethroid that attacks the nervous systems of insects. Chlorfenapyr, on the other hand, is a chemical that targets the mitochondria of cells. While chlorfenapyr is mainly used by professional exterminators, bifenthrin is also used in over-the-counter insecticide sprays, granules, and aerosols.
Gondhalekar points out that these products do work against some populations of bed bugs, and that they are still an important component of pest management. But in order to keep them from losing any more of their effectiveness—and to make sure they remain a useful option for years to come—they should to be used sparingly, he says, alongside non-chemical methods. People have a better chance of getting rid of all of their bed bugs—including those that have developed resistance—if they pair chemicals with alternative solutions that use heat, steam or silica gel, for example.
“People from academia have been promoting the use of integrative approaches for years, but the cost of non-chemical methods can be prohibitive,” Gondhalekar says. Treating with pesticides, on the other hand, is easy and cheap.
Bed bugs aren’t considered dangerous, but their bites can cause itching, allergic reactions and sleepless nights. Infestations can be difficult and time-consuming to eradicate, and can result in financial distress, anxiety and social isolation.
Thankfully, you can take steps to prevent them. Vacuuming regularly, using an insect-proof mattress casing and being cautious when visiting hotels can help keep homes bed-bug free. “If you’re frequently monitoring for bed bugs, then you won’t have the issue of them multiplying into large numbers,” he says. “It’s much easier to manage the problem early, when it’s just five or 10 bed bugs, rather than hundreds or thousands.”