The new work, led by researchers at the American Museum of Natural History and Weill Cornell Medicine, and published today in Nature Communications, could help combat the unwelcome parasites by providing clues on how to overcome their resistance to pesticides. The data also provide a rich genetic resource for mapping bedbug activity in human hosts and in cities, including subways.
“Bedbugs are one of New York City’s most iconic living fossils, along with cockroaches, meaning that their outward appearance has hardly changed throughout their long lineage,” said George Amato, director of the Museum’s Sackler Institute for Comparative Genomics and one of the paper’s corresponding authors. “But despite their static look, we know that they continue to evolve, mostly in ways that make it harder for humans to dissociate with them. This work gives us the genetic basis to explore the bedbug’s basic biology and its adaptation to dense human environments.”
The common bedbug (Cimex lectularius) has been coupled with humans for thousands of years. This species is found in temperate regions and prefers to feed on human blood. In recent decades, the prevalence of heated homes and global air travel have accelerated infestations in urban areas, where bedbugs have constant access to blood meals and opportunities to migrate to new hosts. A resurgence in bedbug infestations since the late 1990s is largely associated with the evolution of the insects’ resistance to known pesticides.
The researchers extracted DNA and RNA from preserved and living collections, including samples from a population that was first collected in 1973 and has been maintained by Museum staff members since then. RNA was sampled from males and females representing each of the bug’s six life stages, before and after blood meals, in order to paint a full picture of the bedbug genome.
“It’s not enough to just sequence a genome, because by itself it does not tell the full story,” said Mark Siddall, a curator in the Museum’s Division of Invertebrate Zoology and one of the paper’s corresponding authors. “In addition to the DNA, you want to get the RNA, or the expressed genes, and you want that not just from a single bedbug, but from both males and females at each part of the life cycle. Then you can really start asking questions about how certain genes relate to blood-feeding, insecticide resistance, and other vital functions.”
The researchers found that the number of genes was fairly consistent throughout the bedbug life cycle, but they observed notable changes in gene expression, especially after the first blood meal. Some genes, expressed only after the bedbug first drinks blood, are linked to insecticide resistance, including mechanisms that result in better detoxification and thicker chitin, or skin. This suggests that bedbugs are likely most vulnerable during the first nymph stage, potentially making it a good target for future insecticides.
In addition, the study incorporated DNA data collected concurrently from more than 1,400 locations across New York City, including every subway station, to look at microbial diversity. They found differences in the genetic makeup of bedbugs that reside in different parts of the city, as measured by traces of DNA on east-west versus north-south subway lines, as well as between borough locations and among surfaces (e.g., benches vs. turnstiles).
The findings suggest that areas of the city in close proximity to each other have bedbug populations that are related, and that bedbugs from one borough can be distinct from those in another borough. This kind of information can be used to map the pathways of migration of bedbug infestations in established and new urban environments.