If bed bugs seem to be everywhere, it’s probably because they are. Some bug watchers have estimated that populations of the tiny, blood-sucking mattress-dwellers have jumped by as much as 500% in recent years, and a 2010 survey found that 95% of exterminators in the U.S. had reported taking care of at least one bed bug infestation in the past year.
Experts say that the increase in international human travel, along with the bugs’ growing resistance to insecticides, is largely responsible for their resurgence. Now researchers have figured out one reason the critters are so hardy: they can inbreed, quite robustly, for generations. (There are a few other insect species that can do this, notably among them cockroaches.) So all it takes to infest an entire apartment building, for example, is one single mated female that hatches her offspring; after that, the brothers and sisters can mate with each other and keep the population booming.
“For the vast majority of insect species, inbreeding is detrimental,” says Coby Schal, a professor of entomology at North Carolina State University, who presented his findings on bed bug inbreeding at the American Society of Tropical Medicine and Hygiene conference in Philadelphia. “‘Inbreeding depression’ occurs, because it leads to mutations that have deleterious effects and eventually kill off the population. But some colonizing species such as cockroaches and bed bugs are resistant to inbreeding depression because they have little opportunity to breed with other populations that might be some distance away — bed bugs can’t fly — so they’ve evolved the ability to withstand extensive inbreeding without deleterious effects.”
PHOTOS: Bed Bugs: the Beauty Shots
In a genetic analysis of bed bugs that Schal and his colleagues conducted in apartment buildings in North Carolina and New Jersey, they found very low genetic diversity among the bugs inhabiting each building. In other words, they were all related. So, rather than accumulating from multiple sources, building infestations tend to be the handiwork of just one or two industrious females. “A single female can produce a very thriving population that can spread through a building very rapidly,” says Schal.
Since most of the bed bugs infesting the U.S. today are the resilient members of their species — resistant to the pyrethroid insecticides that are commonly used to get rid of the bugs worldwide — their inbreeding only serves to spread their chemical resistance. Once these insects seed an infestation in a building, treating them with the standard bug spray might not get rid of them. The only hope is that one of the 300 insecticides registered with the Environmental Protection Agency for use against beg bugs might do the trick.
Interestingly, when Schal and his team compared bed bugs’ genetic makeup across state lines, to determine how the bugs were sustaining their wider populations, they found the exact opposite effect. Instead of being genetically similar, bugs from different states showed a high level of genetic diversity, suggesting that they came from multiple sources rather than a single infestation. This is the worst possible scenario for us, the humans hosts, and the best possible scenario for the bugs. They’re hitching free rides across oceans and continents to find new homes to infest, and once there, where almost any other species would require a village to survive, all they need is a single mated female to thrive.
“We think that global transport and travel are bringing highly resistant bed bugs to the U.S., and through their ability to withstand inbreeding, they are generating large populations wherever they land,” says Schal.
The lesson from all this analysis? Detecting and dispatching bed bugs as early as possible in their infestation will keep them from spreading (they do like to mate, after all). So if you’re in an office or an apartment building and you see the telltale signs of infestation — whitish egg casings or rusty stains (left from crushed bed bugs) on your bedding or mattress — don’t just hope the problem will go away. It won’t. Alert your superintendent immediately, so that a professional exterminator can be brought in to kill the bugs before they breed the next generation — and the next, and the next, and the next.