Two insecticides commonly used to kill bed bugs are becoming less effective against them, according to a study published today in the Journal of Economic Entomology.

In the past 15 years, there has been a resurgence of bed bugs throughout the U.S., and people often struggle to rid their homes of the hardy pests, known for causing itchy red welts.

After the bugs developed resistance against many of the most powerful pesticides, such as DDT, exterminators had been increasingly relying on two chemicals—chlorfenapyr and bifenthrin. But until now, no one had looked at whether bed bugs were developing defenses against these chemicals too, says Ameya D. Gondhalekar, one of the study authors and a research assistant professor at the Center for Urban and Industrial Pest Management at the Department of Entomology at Purdue University.

Gondhalekar and his team exposed 10 different groups of bed bugs collected from different parts of the country to each of the chemicals in a glass vial. After several days, they examined how effective the chemicals were at killing the bugs.

While most of the bed bugs were wiped out by the chemicals, three groups continued to thrive after being treated with chlorfenapyr, and five groups were still kicking after being treated with bifenthrin. That means that while some bed bugs will respond to these chemicals, others won't—and it's likely that more and more bugs will become resistant over time.

“This is just more evidence that this pesticide-only approach to controlling bed bugs isn’t really working,” says Consumer Reports’ senior scientist Michael Hansen, Ph.D. “The take-away is that if you want to control these bed bugs, you can’t just spray.” 

How to Prevent a Bed Bug Infestation

Prevention and vigilance are key to preventing a bed bug problem. “It’s much easier to control them if they are found early, [when there are only a few of them], as opposed to when they grow to number in the hundreds,” says Gondhalekar.

Monitor your home. Bed bugs like to hide in cracks and crevices like walls, luggage, boxes, and clothing, but since they feed on humans while they sleep, they’re most commonly found in beds. If you suspect an infestation, or if you live in an apartment building with a bed bug problem, regularly inspect your bed sheets, mattress (including underneath), and box-spring seams for bugs. They’re flat and oval-shaped, with red or brown bodies, roughly the size of an apple seed. Watch for adults, nymphs, and eggs, as well as exoskeletons (casings that the bugs leave behind when they molt) and dark, rust-colored spots (feces).

Encase your mattress. Enclosing your mattress, pillows, and box spring with a protective cover can block bed bugs from reaching their favorite hiding place.

Be cautious when you travel. Hotel and motel rooms are hotbeds for bed bugs. When checking in, put your luggage in the bathroom, then inspect the bedding. Stow your suitcases on a luggage rack or a hard surface.

When you return home, quarantine your bags. Decontaminate your luggage and clothing by putting your entire suitcase into a large chest freezer (if you have one) for four days, suggests Gondhalekar, before bringing them back into your home. Extreme hot or cold temperatures kills bed bugs. You can also put your clothes in the dryer on a hot setting for 30 minutes, and try steam cleaning your luggage and clothing.

How to Treat a Bed Bug Infestation

Minimize its spread. First, notify your landlord if you rent in a building to control its spread to other units. Thoroughly vacuum any infested areas, including carpets and mattresses, and then empty the vacuum bag into a plastic bag, seal it, and throw it in the trash outside. If you can’t get the bed bugs out of your furniture, discard items in a responsible manner. To avoid someone else from salvaging infested furniture or mattreses, rip, remove stuffing, or spray paint with the words “bed bugs.”

Bring on the heat. Heating infested furniture or the entire apartment to a very high temperature—more than 100 degrees, in most cases—will kill bed bugs. If you have a hand-held steamer, blast cracks and crevices. 

Use an insecticide alternative. Substances such as diatomaceous earth, boric acid, and silica gel kill bed bugs by damaging their outer coating so they dry out and die. Put these powders into cracks and crevices around your home (being careful not to ingest or inhale them).

Enlist professional help. Not all bed bugs respond the same way to insecticides, so if you have an infestation that you can’t control yourself, a professional can help you determine the correct treatment or insecticide to use.