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Researchers have successfully mapped the genomes of a susceptible bed bug strain and a highly resistant superstrain, revealing remarkable insights into their genetic mutations linked to insecticide resistance. This new research provides the most comprehensive overview yet of the mutation landscape in these pests.
The results of this study were published in the journal Insects.
While bed bugs are not known to transmit diseases to humans, their bites can lead to uncomfortable rashes and, in some cases, secondary infections. The implementation of widespread insecticide use, including the notorious DDT, nearly eradicated these pests by the 1960s. However, over the last two decades, bed bugs have made a notable comeback, partly due to adaptive mutations enabling them to resist various insecticides.
Resistance in bed bugs can arise via several mechanisms: they may produce enzymes that decompose insecticides (known as metabolic resistance) or develop thicker exoskeletons that block chemical penetration (referred to as penetration resistance). Though past research has documented some mutations and gene expressions associated with this resistance, a complete understanding has been hampered by the lack of comprehensive genome sequencing in resistant strains.
To fill this knowledge gap, a research team spearheaded by Hidemasa Bono, a professor at Hiroshima University’s Graduate School of Integrated Sciences for Life, undertook genome mapping of both susceptible and resistant bed bug strains from Japan. The susceptible lineage descends from wild bed bugs (Cimex lectularius) collected 68 years ago in fields near Isahaya City, Nagasaki, while the resistant specimens were derived from bugs collected at a hotel in Hiroshima City in 2010. Tests revealed that the resistant strain exhibited a staggering 19,859-fold increase in resistance to pyrethroids, the main insecticides employed in bed bug control, which far surpasses previously observed superstrains. All samples were sourced from Fumakilla Limited, a chemical manufacturing company based in Japan.
Genome Sequencing: A Complex Puzzle
Sequencing a genome resembles assembling an extensive jigsaw puzzle that can range dramatically in size. Utilizing a cutting-edge long-read sequencing technique, researchers were able to construct the most complete bed bug genomes to date. This method captures longer DNA sequences, enabling them to piece together larger sections of the genome, in contrast to traditional short-read sequencing that often leaves incomplete and fragmented images.
The researchers achieved 97.8% completeness and a quality value (QV) of 57.0 for the susceptible strain, and 94.9% completeness with a QV of 56.9 for the resistant strain. Generally, a QV above 30 indicates high-quality sequencing with an error rate of less than 0.1%. Both genomes surpassed the N50 value of the previously sequenced C. lectularius reference genome, suggesting fewer gaps and a more cohesive genomic representation.
Discovery of Resistance Mutations
Following genome sequencing, the team was able to identify and analyze protein-coding genes, determining their functions through transcription analysis. The study found 3,938 transcripts with amino acid mismatches, out of which 729 mutated transcripts were specifically associated with insecticide resistance.
“By determining the genome sequence of insecticide-resistant bed bugs, which demonstrated a 20,000-fold increase in resistance compared to their susceptible counterparts, we were able to identify 729 transcripts with unique mutations related to resistance,” explained Kouhei Toga, the study’s first author and a postdoctoral researcher at Hiroshima University.
“The genes linked to these transcripts were involved in critical biological processes such as DNA damage response, cell cycle regulation, insulin metabolism, and lysosome functionality. This indicates that these molecular pathways could contribute to the establishment of pyrethroid resistance in bed bugs.”
Drawing from prior research in insects, the team validated known resistance mutations and uncovered new ones, which could lead to more targeted and effective pest management strategies in the future.
“Our findings have identified numerous genes potentially involved in insecticide resistance that haven’t been previously documented in relation to bed bugs. Genome editing of these genes may offer significant insights into the evolutionary pathways and mechanisms of insecticide resistance,” added Toga.
“This research also broadens the array of target genes for monitoring changes in allele distribution and resistance levels in natural bed bug populations. It exemplifies the promise of genome-wide approaches to deepen our understanding of insecticide resistance in these notorious pests,” concluded Toga.
Other members of the research team included Fumiko Kimoto and Hiroki Fujii, who are affiliated with Fumakilla Limited.
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