Bed Bugs Are Becoming Resistant to All of Our Insecticides—This Fungus Might Help

If you have encountered bed bugs lately, you are not alone. While the pesticides used to fight these pests are losing effectiveness, a fungus shows promise in knocking the bugs out of beds everywhere.

Bed bugs, or Cimex lectularius, are parasitic arthropods, part of a broad group that includes ticks, mites, and mosquitoes. They feed on the blood of humans and other animals. Although they are known to carry at least 40 pathogens, there is no evidence that bed bugs transmit diseases to humans, although some experience an allergic reaction to their bite.

Bed bugs have been bugging humans for literally ages. Dating between 5,000 and 11,000 years old, archaeologists recently found the oldest known remains of a bed bug relative in a cave in southern Oregon. Mentioned by the Greeks as early as 400 BC, bed bugs spread across the globe without meeting much resistance until the development of powerful insecticides, like DDT, which were later banned as health hazards.

By the 1990s, bed bugs were making a comeback. Scientists suggest increased travel, ineffective control measures, and the capability of bed bugs to develop chemical resistance are some of the reasons for the resurgence.

Wingless, flat, and small, bed bugs are expert at hiding in beds, furniture, luggage, and any small space in between. They can go months without feeding and congregate where humans sleep. Hotels, dorms, and apartment buildings are prime bed bug territory, but recently they have been found in schools and an Iowa hospital.

According to the Centers for Disease Control and Prevention, you could have a bed bug problem if you notice any of the following:

• Flat, reddish brown insects on the ground, on your sheets, or anywhere nearby.
• Bed bugs molt, leaving their crusty worn-out exoskeleton behind.
• Small red-brown spots caused by bed bug feces.
• Bites on your arms, face, legs, or body. Bite marks sometimes do not appear for upwards of two weeks.

Bed bugs have a keen capability to adapt to insecticides used to kill them. Their tough exoskeleton takes the brunt of pesticide applications and studies show that the rugged outer shell contains genetic material that has mutated to resist pesticides, slow the progression of the pesticide, and then detoxify the chemical before it reaches the nerve cells of the bed bug that is its target.

Recent research from the Department of Entomology at Purdue University, published in the Journal of Economic Entomology, used ten different strains of bed bugs to evaluate resistance to two commonly used insecticides, chlorfenapyr and bifenthrin. The bed bugs were collected from different geographic regions, including Virginia, Tennessee, Ohio, New Jersey, and Washington, DC.

Testing the bed bug populations, researchers determined three of the ten groups were resistant to the insecticide chlorfenapyr, while five of the ten strains of bed bugs were resistant to bifenthrin. In a press release, study author Ameya Gondhalekar said, "In the past, bed bugs have repeatedly shown the ability to develop resistance to products overly relied upon for their control. The findings of the current study also show similar trends in regard to chlorfenapyr and bifenthrin resistance development in bed bugs."

Cimex lectularius taking a blood meal.

As the effectiveness of these insecticides wane, researchers at Penn State University are testing a new pesticide that uses a fungus, instead of chemicals, to control and eradicate bed bugs.

In a different study published in the journal Pesticide Management Science, researchers evaluated a biopesticide that uses a natural soil-dwelling fungus, Beauveria bassiana, to infect and kill bed bugs.

Originally identified as a culprit in the silkworm industry, the fungus B. bassiana is becoming an important biocontrol for a variety of insect pests like Colorado Potato Beetle, ants, mealybugs, and others.

B. bassiana causes white muscadine disease, a fungal infection that shrouds the insect in fungus. When the fungus is exposed to the outer skin, or cuticle, of a susceptible insect, the fungus penetrates through the cuticle directly into the body of the insect. Once inside, it colonizes the body, draining its fluid and nutrients. It eventually grows back out of the insect, swaddling it in a cocoon of fungal spores, killing the insect.

A caterpillar infected with Beauveria bassiana.

In testing the bioinsecticide Aprehend, developed at Penn State, the research team found B. bassiana offers significant advantages for bed bug control, including:

• Unlike chemical insecticides, the fungus did not have to be sprayed directly on the bed bug. Applied to a fabric commonly used for bed box springs, the bed bugs walk through the spores and return to their hiding places. By grooming, and through contact with other bed bugs, the spores infect the individual and its cohort—wherever they hide. Only a small number of bed bugs needed to be exposed in order to infect the entire population of bed bugs.
• The bioinsecticide was effective against each of the strains of bed bugs tested in the research. These strains included bed bugs that were resistant to insecticides and those that were not. Approximately 95% to 99% of the bed bugs were killed within 14 days.
• Because the mechanism used by B. bassiana is completely different than an insecticide, the bed bugs have no known resistance to it, unlike the insecticides used at present. Senior Research Associate Nina Jenkins said, "B. bassiana has a unique mode of action with no known resistance or cross-resistance in bedbugs, and it is highly effective on pyrethroid-resistant bed bugs, making it an excellent candidate for use in bed bug management."
• One application of the fungal biopesticide persists for three months and can be applied as a barrier product to prevent infection. Jenkins added, "We can't prevent bed bugs from coming in, but if we can maximize the chances of bed bugs crossing a sprayed barrier on their way to or from their hideout, we can prevent an infestation from establishing."

Sticking to bed bug legs like wet sand, the fungal infection begins to colonize bed bugs within 20 hours of exposure

You might wonder if the fungus is bad for bed bugs—what about humans? Jenkins replied, "Beauveria bassiana is an insect disease, it does not infect humans and is non-toxic. However, our use strategy also ensures that humans do not come into direct contact with the spores. They are sprayed onto surfaces such as the rear side of the headboard, underside of the box spring etc. This ensures that the barriers applied are not removed by human contact and remain effective for 3 months."

She added:

Once applied to a surface, the spores stay in place unless physically removed either by the bed bugs walking over the sprayed surface, or by wiping or rubbing. The spores will not be in the air after application. There is no long-term human exposure risk.

The fungal bioinsectide, and a specialized sprayer, is in development, with hopes to have it in the hands of professional pest controllers later this year. In the meantime, greater use of integrated pest management methods like traps, mattress encasement, steam heat, and other techniques may slow the development of chemical resistance in bed bugs.

According to the annual survey of the top 50 cities for bed bug infestation by pest management company Orkin, the top five cities for bed bugs in the US include Baltimore, Washington, DC, Chicago, New York, and Columbus, Ohio. In a press release, Orkin Entomologist Ron Harrison added, "We have more people affected by bed bugs in the United States now than ever before. They were virtually unheard of in the U.S. 10 years ago."

If you find bed bugs, contact a pest management company for tips and options on giving bed bugs the boot.

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Cover image by Janice Haney Carr/CDC