Following World War II in the 1950s, bedbug infestations were almost eradicated worldwide through the use of the insecticide dichlorodiphenyltrichloroethane, better known as DDT, a chemical that has since been banned. However, urban pests have since resurged around the world, and they have developed resistance to a range of insecticides used to control them.
A study published in the Journal of Medical Entomology details how a research team from Virginia Tech, led by urban entomologist Warren Booth, discovered genetic mutations that can lead to insecticide resistance.
The discovery was the result of research Booth organized for graduate student Camilla Block to improve her skills in molecular research.
Booth, who specializes in urban pests, had long noticed a genetic mutation in the nerve cells of German cockroaches and whiteflies that made them resistant to pesticides. Booth suggested that Block take a sample of one bed bug from each of 134 different bed bug populations collected by North American pest control companies between 2008 and 2022 to see if they all had the same cell mutation. The results showed that two bed bugs from two different populations had the same cell mutation.
“These are actually my last 24 samples,” said Bullock, who studies entomology and is a member of the Invasive Species Partnership. “I’ve never done molecular research before, so having all these molecular skills was critical for me.”
Because bedbug infestations are genetically uniform due to mass inbreeding, only one specimen from each sample is typically representative of the population. But Booth wanted to confirm that Bullock had indeed found the mutation, so they tested all samples from both identified populations.
”When we went back and screened a few individuals from both populations, we found that every single one of them carried the mutation,” Booth said. “So their mutations are fixed, and they’re the same mutations that we found in the German cockroach.”
By studying German cockroaches, Booth learned that their resistance to insecticides was due to genetic mutations in the cells of the nervous system and that these mechanisms were environmentally determined.
“There is a gene called the Rdl gene. This gene has been found in many other pest species and is associated with resistance to an insecticide called dieldrin,” said Booth, who also works at the Fralin Institute of Life Sciences. “This mutation is present in all German cockroaches. It’s surprising that we haven’t found a population without this mutation.”
Fipronil and dieldrin, two insecticides that have been shown to be effective against bed bugs in the lab, work by the same mechanism of action, so the mutation theoretically made the pest resistant to both, Booth said. Dieldrin has been banned since the 1990s, but fipronil is now used only for topical flea control on cats and dogs, not for bed bugs.
Booth suspects that many pet owners who use topical fipronil treatments allow their cats and dogs to sleep with them, exposing their bedding to fipronil residue. If bed bugs were introduced into such an environment, they could be inadvertently exposed to fipronil, and then the mutation could be selected for in the bed bug population.
”We don’t know whether this mutation is new, whether it arose after this, whether it arose during this time period, or whether it was already present in the population 100 years ago,” Booth said.
The next step will be to expand the search and look for these mutations in different parts of the world, especially in Europe, and at different times among museum specimens, since bed bugs have been around for over a million years.
In November 2024, Booth’s lab successfully sequenced the entire genome of the common bed bug for the first time.
Booth noted that the problem with museum DNA is that it breaks down into small fragments very quickly, but now that researchers have templates at the chromosome level, they can take those fragments and rearrange them into chromosomes, reconstructing genes and the genome.
Booth noted that his lab partners with pest control companies, so their genetic sequencing work could help them better understand where bed bugs are found around the world and how to help get rid of them.
Now that Bullock has honed her molecular skills, she’s looking forward to continuing her research into urban evolution.
”I love evolution. I think it’s really interesting,” Block said. “People are developing a deeper connection with these urban species, and I think it’s easier to get people interested in bed bugs because they can relate to it firsthand.”
Post time: May-13-2025