Scientists mapped nearly error-free genomes of a susceptible strain of bed bugs and a superstrain about 20,000 times more resistant to insecticides, offering the broadest view yet of the full extent of their resistance mutations.
Their findings were published in the journal insects.
Although there is no evidence that bed bugs transmit diseases to humans, their bites can cause itchy rashes and secondary skin infections. Widespread use of insecticides, including the now-banned DDT, nearly wiped out populations of these blood-sucking insects in the 1960s, making infestations rare. But in the last 20 years, the world has witnessed their resurgence, in part due to the resistance mutations they developed against these insecticides.
Resistance can occur through different mechanisms, such as the production of enzymes that detoxify insecticides (metabolic resistance) or the development of thicker outer layers to block the chemicals (penetration resistance). Previous studies have identified some of the mutations and gene expressions related to insecticide resistance. However, the full extent of the mutations driving resistance is still unknown, as no research has sequenced the entire genome of insecticide-resistant strains.
A research team led by Hidemasa Bono, professor at the Graduate School of Integrated Life Sciences at Hiroshima University (HU), mapped genomes of susceptible and resistant bed bug strains from Japan to address this gap. They obtained susceptible strains descended from wild stink bugs (Cimex lectularius) collected 68 years ago in fields in the city of Isahaya, Nagasaki. Meanwhile, the resistant strains were created from specimens collected at a hotel in the city of Hiroshima in 2010. Their tests revealed that the resistant samples had 19,859 times greater resistance to pyrethroids, the insecticide most commonly used for pest control. bed bugs, exceeding levels observed in many previously identified superstrains. All samples were provided by Fumakilla Limited, a chemical manufacturing company based in Japan.
Putting together the genome puzzle
Sequencing a genome is like putting together a huge puzzle, encompassing between 160,000 and 160 billion pieces. To map the most complete bed bug genomes to date, researchers used the innovative long-read sequencing method, which captures longer stretches of DNA, similar to having entire sections of puzzle pieces put together. In contrast, traditional short-read sequencing only covers small fragments, often resulting in frustrating gaps.
The researchers put together a near-total picture of the two genomes with almost every piece exactly where it belonged, achieving 97.8% completeness and a quality value (QV) of 57.0 for the susceptible strain and 94.9% for integrity and a QV of 56.9 for the resistant strain. . A QV greater than 30 indicates high-quality sequences with an error rate less than 0.1%. Both also exceeded the N50 value of the existing C. lectularius reference genome, Clec2.1, from a previous sequencing effort, meaning there were fewer gaps and more complete sections of the genome puzzle.
Known and discovered resistance mutations
After completely sequencing the genomes, the team identified protein-coding genes, determined their functions, and assessed whether they were active using transcriptional analysis. They discovered 3,938 transcripts with amino acid discrepancies. Of these, 729 mutated transcripts were related to insecticide resistance.
“We determined the genome sequence of insecticide-resistant bed bugs, which exhibited 20,000 times greater resistance compared to susceptible bed bugs. By comparing amino acid sequences between susceptible and resistant bed bugs, we identified 729 transcripts with resistance-specific mutations, “said the study’s first author, Kouhei Toga, a postdoctoral researcher in the Genome Informatics Laboratory at the Graduate School of Integrated Life Sciences. HU.
“These transcripts included genes related to DNA damage response, cell cycle regulation, insulin metabolism and lysosome functions. This suggests that these molecular pathways may play a role in the development of resistance to pyrethroids in bed bugs”.
Building on previous insect studies, the researchers confirmed known resistance mutations and discovered new ones that could inform more targeted and effective pest control strategies.
“We identified a large number of genes likely involved in insecticide resistance, many of which had not previously been reported to be associated with resistance in bed bugs. Genome editing of these genes could provide valuable insights into the evolution and mechanisms of insecticide resistance,” Toga said.
“Furthermore, this study expands the set of target genes to monitor allele distribution and frequency changes, which could significantly contribute to assessing resistance levels in wild populations. This work highlights the potential of genome-wide approaches.” to understand insecticide resistance in bed bugs.
Other members of the investigation team include Fumiko Kimoto and Hiroki Fujii, who are employees of Fumakilla Limited.