France is currently grappling with a pervasive bed bug infestation. This year, reports of bed bug sightings in Paris have surfaced in a variety of locations, including schools, trains, hospitals, and cinemas. However, the problem has been steadily escalating over time. In 2020, a French hospital had to shut down an entire unit due to a bed bug outbreak triggered by a patient's admission. A sniffer dog investigation revealed infestations in four rooms, prompting the 24-day closure.

This phenomenon seems to be part of a broader "global resurgence" of bed bugs that has witnessed these small, oval-shaped insects, smaller than a grain of rice, evolving into a mounting issue in cities worldwide over the past two decades. The ease of global travel, which allows these blood-sucking insects to traverse continents inconspicuously in the luggage of unwitting travelers, has facilitated their spread. Yet, once they establish themselves in an area, recent research suggests that they may also be growing more challenging to eradicate.

In 2005, Warren Booth, then a young postdoc researcher in North Carolina, embarked on a seemingly peculiar quest. He reached out to pest control companies and requested common bed bugs, scientifically known as Cimex lectularius. Between 2005 and 2009, he gathered 161 specimens from 38 different infestations across 38 U.S. states, with the intention of studying them. However, his research was cut short when he was offered a geneticist position at the University of Tulsa.

A decade and a half later, he joined forces with his graduate student, Cari Lewis, who had accumulated a substantial collection of 233 bed bugs collected from various U.S. states during the years 2018 to 2019. Their combined resources were quite impressive, but they faced a crucial question: how to put this treasure trove to use? Leveraging their expertise in genetics, they embarked on the task of sequencing the DNA of these bed bugs.

Their primary objective was to identify mutations within a specific region of the genome responsible for encoding the sodium channel. This channel plays a vital role in nerve function, a common feature in both bed bugs and humans. Situated within the cell membrane of every neuron in the body, the sodium channel opens, permitting the flow of positively charged sodium ions from the exterior to the interior of the neuron. This event triggers a neuronal "spike," facilitating the transmission of messages throughout the body.

Sodium channels are indispensable for survival, yet certain substances, such as the prohibited pesticide DDT and pyrethroid insecticides, disrupt their proper functioning. Pyrethroid insecticides, readily available as over-the-counter solutions for bed bug infestations, and DDT, both interact with sodium channels and prevent them from closing.

"The nerve continuously triggers, leading to paralysis and ultimately the demise of the creature," explains Booth, currently serving as an associate professor of urban entomology at Virginia Tech University in Blacksburg, United States.

Over time, bed bugs have developed three distinct mutations in the genes responsible for coding sodium channels. These mutations effectively thwart the binding of insecticides to these channels. While the precise period when these mutations emerged remains uncertain, they have been present since at least the 1950s, following the widespread deployment of DDT during World War Two.

Nonetheless, assessing the prevalence of these mutations within the bed bug population has proven challenging until now.

The research conducted by Booth and Lewis revealed that 36% of the older bed bugs collected in the United States between 2005 and 2009 possessed a single mutation in their sodium channel gene, while 50% exhibited two mutations. A mere 2.5% of the population had no mutations, rendering them vulnerable to insecticides.

Tactics of Bed Bugs: Why They're Most Active While You Sleep

Bed bugs are most active between midnight and 5 a.m. when we're in deep sleep, making them harder to detect.

They locate their human hosts through carbon dioxide emissions and body heat, even if you're not sleeping near their hiding spots.
Mutations in their genes have made them highly resistant to insecticides, with 84% of recent samples having both mutations, rendering them impervious to common over-the-counter solutions.

Professional pest control is essential, as standard insecticides are ineffective against these resilient pests. The notoriety of bed bug infestations in Paris prompted Eurostar to implement specialized cleaning procedures on trains between France and England.

Booth and Lewis attribute this shift to the widespread reliance on readily available, non-prescription insecticides.

"People often opt for a quick fix, purchasing a $5.99 (£4.90) bottle of insecticide at the local hardware store," explains Booth. "Regrettably, in doing so, they inadvertently favor the bed bugs with these mutations. They eradicate the susceptible ones while enabling the resistant ones to thrive."

Consequently, bed bugs with genes susceptible to these insecticides fail to pass on their genetic material, whereas the resistant ones proliferate, resulting in an increasingly resilient bed bug population that's challenging to eliminate.

So, does the same pattern apply globally?

In 2018, Booth collaborated with Ondřej Balvín, an ecologist at the Czech University of Life Sciences in Prague, to conduct gene sequencing on 393 bed bugs collected from 131 distinct infestation locations throughout Europe. The sampled countries included the UK, France, Germany, Switzerland, Italy, Poland, Sweden, and others. Their findings indicated that a mere 3.8% of bed bugs displayed susceptibility to pyrethroid insecticides, while 93.5% of bed bugs possessed a single mutation. Unlike the situation in the United States, however, none of the European bed bugs had acquired two mutations.

It appears that a unique evolutionary phenomenon was at play in the United States, driving a higher mutation rate among bed bug populations. It is conceivable that at some point in the past, a single-mutation-carrying female bed bug randomly acquired a second mutation, essentially rendering it immune to over-the-counter insecticides. This variant then rapidly propagated throughout the population.

Strategies in the Battle Against Bed Bugs

In the ongoing fight against bed bugs, one of the options on the table is heat treatment, a process involving elevating the room or entire property's temperature to extreme levels. In a recent study, researchers collected 5,400 adult bed bugs from 17 infested locations in Paris. These bugs were then segregated into five groups, each placed in different containers to replicate their natural habitats. Some bed bugs found refuge among furniture remnants, mattress or blanket scraps, while others remained exposed to the open air.

Subsequently, the researchers exposed these bugs to elevated temperatures. Astonishingly, all the bed bugs succumbed after just one hour of being subjected to 60°C heat.

However, a study conducted in 2021 unveiled a bed bug behavior that complicates heat treatment efforts. Bed bugs tend to flee when exposed to excessive heat, which presents a challenge, especially in multi-story apartment buildings. In such scenarios, bed bugs could easily migrate from one apartment to another, infiltrating unsuspecting neighbors' living spaces. It's worth noting that attempting heat treatment at home is strongly discouraged.

Warren Booth emphasizes, "Never attempt heat treatment yourself. There have been reports of individuals using propane heaters and inadvertently causing fires in their homes. This approach not only proves ineffective against bed bugs but also poses a greater risk to your safety than to the bed bugs."

In contrast to chemical pesticides, which necessitate direct and prolonged contact to prove lethal, the fungus spores adhere to bedbugs as they traverse the treated surface. Once these spores are on the bed bugs, the insects distribute them through self-grooming, and within 20 hours of exposure, the spores begin to grow and establish colonies within the bed bugs' bodies. In light of this innovative approach, Jenkins has established a spin-out company to market this product.

Jenkins elaborates, stating, "Bed bugs only need a brief encounter with the treated surface to acquire the spores and become infected. Exposed bed bugs also transport the spores back to their concealed hiding spots, thereby infecting other bed bugs within the population. This tactic proves effective because bed bugs are 'obligate blood feeders,' obliging them to venture from their concealed shelters in search of a blood meal."