From fleas to mosquitoes, there's no shortage of organisms we like to consider pests – and, not surprisingly, the majority are insects, which account for up to 90% of animals on the planet. But thanks to new genetic detective work, scientists have found the very first species that got a taste for humans – and we're still the main dish on its menu, some 60,000 years on.
Virginia Tech researchers made this discovery after comparing the genomes of two distinct lineages of bed bugs – one that is suspected to have hitched a ride on a Neanderthal thousands of years ago, and another that stuck with its bat host. What they found was that while the insect population feeding on bats declined over thousands of years, the bed bugs we know today evolved as humans did – which sets them up as our oldest known "pest."
“We wanted to look at changes in effective population size, which is the number of breeding individuals that are contributing to the next generation, because that can tell you what’s been happening in their past,” said Lindsay Miles, lead author and researcher in Virginia Tech's Department of Entomology. “Initially with both populations, we saw a general decline that is consistent with the Last Glacial Maximum; the bat-associated lineage never bounced back, and it is still decreasing in size.”
“The really exciting part is that the human-associated lineage did recover and their effective population increased," she added.
While studies have found that bed bugs have been on Earth since the dinosaurs, the estimated 90 species of the arthropods shared a fairly stable symbiotic relationship with their hosts – until human ancestors began forming societies and living in close proximity. It was then that the common bed bug (Cimex lectularius) and the tropical kind (Cimex hemipterus) forged an enduring path of survival.
“That makes sense because modern humans moved out of caves about 60,000 years ago,” said Warren Booth, an Entomology Associate Professor at Virginia Tech. “There were bed bugs living in the caves with these humans, and when they moved out they took a subset of the population with them so there’s less genetic diversity in that human-associated lineage.”
Anyone who has had to deal with a bed bug infestation will know how difficult they are to eradicate – while this is partly due to their numbers and reproduction rate, recent research has also identified a genetic mutation that made them resistant to a formerly effective insecticide.
“What will be interesting is to look at what’s happening in the last 100 to 120 years,” said Booth. “Bed bugs were pretty common in the old world, but once DDT [dichloro-diphenyl-trichloroethane] was introduced for pest control, populations crashed. They were thought to have been essentially eradicated, but within five years they started reappearing and were resisting the pesticide.”
And while you'd be hard-pressed to find any fans of bed bugs, there's something to admire in their adaptability and opportunistic evolutionary path, from finding a new home with a caveman host to their rapid adaptation to withstand DDT. Since that mutation, and the phasing out of DDT, an uptick in international travel and increasing urban population density, bed bug numbers have exploded. In 2006, Australian pest control professionals estimated that infestations soared 4,500% in a year, and you'll find the insects in every US state, concentrated in the most populated areas.
Why does this matter, besides giving us another thing to worry about in bed at night? Well, the sturdy insect's resilience and rapid adaptations can help scientists design more accurate epidemiological models to better predict disease outbreaks as urban populations continue to grow, as well as develop ways to tackle infestations that evade existing and potential resistance.
Ultimately, however, the study is a fascinating insight into just how long the lives of humans and bed bugs have been intertwined – and, sadly for us, it's a relationship that's unlikely to end anytime soon.
"The timing and magnitude of the demographic patterns provide compelling evidence that the human-associated lineage closely tracked the demographic history of modern humans and their movement into the first cities," the researchers noted. "As such, bed bugs may represent the first true urban pest insect species."
While they've proved their resilience, bed bugs are not invincible; the US Environmental Protection Agency has published a thorough guide on handling them without pest control professionals, and it's worth remembering that while their bites are irritating, and can even form large welts on the skin, they don't carry diseases.
As to whether bed bugs or cockroaches will be most successful as life on Earth dwindles, entomologists can't say. While bed bugs have a favored host, their specialist diet is no match for the insect world's ultimate survivor, the German cockroach (Blattella germanica), a generalist feeder that can tolerate broader environmental conditions and has also developed resistance to a range of chemical insecticides. Oh, and they also happen to eat bed bugs.
The study was published in the journal Biology Letters.
Source: Virginia Tech
