If you live in a city, the word “bedbug” is like an icy dagger to the heart. The blood-suckers rely on humans to survive, and they’re great at hopping from one apartment (or person) to another. They’re also increasingly resistant to insecticides.
But don’t pledge fealty to our mattress-dwelling overlords just yet: in a pair of papers published in February in “Nature Communications”, two teams of researchers report the first ever complete genome sequencing for the pest.
Sequencing an organism’s genome — figuring out what genes it has and where they all go — makes studying it much, much easier. This information allows scientists to figure out what particular genes do, how they work together and how they might be related to genes found in other organisms.
Until recently, DNA sequencing was slow and expensive enough to limit its use in the lab. These days it’s just a question of which creature a researcher wants to tackle next. That’s why so many genomic finds are published in pairs: when labs around the world all have the ability to investigate any genome they think might be useful, a few are bound to end up working on the same project simultaneously.
The interest in bedbugs is pretty obvious: the common bedbug (Cimex lectularius) has been feeding off of humans for most (if not all) of our species’s history. They cause pain in the form of welts and rashes, but they also cause emotional anguish — especially in cities, where many may worry that playing host to the bugs will make them patient zero for an embarrassing epidemic.
The insects can be nearly impossible to get rid of (especially if they can simply slip to the apartment next door and come back when you’re done cleaning like mad) and recent studies have painted a dire picture for insecticide use: in one published in January, scientists found that killing recently collected bedbugs required more than 30,000 times more insecticide than was needed to kill bugs that had been bred in the lab for 30 years.
But if scientists can figure out what makes a bedbug bite, they might be able to stop it from doing so.
“At this time, there is no ‘silver bullet’ for impacting a specific gene to control bed bug potentials,” The University of Cincinnati’s Joshua Benoit, corresponding author on one of the two papers, said. But, he added, “the presence of a nearly complete genome will make identifying potential targets much easier.”
“Work on bedbugs previous to this was like feeling your way in the dark,” said George Amato, director of the American Museum of Natural History’s Sackler Institute for Comparative Genomics and an author on the second paper. “By providing this genome — it’s like turning a light on. Now researchers know better how to explore.”
Amato and his AMNH colleagues (along with researchers from Weill Cornell Medicine) were interested in the bedbug’s status as a “living fossil”. That’s a term that gets misused a lot — contrary to popular belief, it doesn’t actually mean that an organism hasn’t changed at all in thousands or millions of years. Every organism continues to evolve over time. But when it comes to living fossils, that evolution results in surprisingly few outward signs of change.
“We had this 60 million year old bedbug in amber that, when you look at it, it looks essentially identical to bedbugs today, even though that specimen obviously predates them feeding on people by a lot,” Amato said. “The naive idea was that maybe by looking at their genomes, we might find something unique to explain why they seemed unchanged.”
The team failed to find any living fossil smoking guns. The bedbug’s genes aren’t organised in a particularly unique way, suggesting that their unchanged appearance has less to do with a genetic quirk than it does with natural selection. In other words, bedbugs might simply have achieved an ideal physical form awfully early — one that happened to support their future run-in with humanity.
Both studies found evidence that bedbugs have borrowed genes from bacteria through a process called horizontal gene transfer, and that bedbugs — like humans — have an extensive ecosystem of microorganisms that live in and on them.
“It’s important to figure out what impact that had on bedbugs, and on their success,” Amato said. It’s possible that there are bacteria tantamount to bedbug survival, and that targeting them could provide another line of defence against the pests.
Benoit’s study, which was completed by 36 collaborating labs, found genes that help female bedbugs survive the violent act of copulation — where the male stabs the female in the abdomen.
It goes without saying that infestations would end a lot quicker if females couldn’t push through this traumatic mating event, so understanding the genes that make it possible could help scientists weaken the species.
Now that these two groups have given other scientists have a roadmap to guide them, we can start our journey towards a bedbug-less Utopia — or at least a world where they’re not so impossible to get rid of. But it could obviously take a while to figure out how to thwart bedbugs for good. In the meantime, Amato and his colleagues are exploring another portion of their experiment.
In addition to sequencing the bedbug genome, the researchers collected samples from New York City subways and went searching for traces of bedbug DNA inside. Now that they have the whole genome, they’re able to pluck bedbug DNA from a soup of subway trash and know that a bug was recently in the vicinity — sort of.
This same method of DNA spelunking has been called into question before, and it’s easy to get a false positive for all manner of species.
But if AMNH’s findings are correct, the DNA samples uncover something interesting: the researchers found that bugs in the same borough are more closely related to one another than pests from different ‘hoods. So what makes a Brooklyn bedbug different from a bug in the Bronx? That’s still unclear.
“We mostly saw differences in neutral markers, so it’s not as if they’ve adapted to do different things in different boroughs,” Amato said. But their differences could indicate migration patterns, showing researchers where bedbugs are able to migrate and what roadblocks trip them up, keeping them isolated from other groups.
“It’s an indication that something is structuring their population,” Amato said. “What’s kept them separate? Is it about how people are moving them around, or is it some geographic barrier, or even some kind environmental block, such as construction? These differences can tell us about the distribution and movement of the animals.”
A way of mapping bedbug migration could easily be as disturbing as it would be helpful. But when an insect has spent tens or even hundreds of thousands of years feeding off of your ancestors, you should probably take all the help you can get.
Courtesy Washington Post