Within each domestic population, however, the genetic distribution is a much different story. In a single home or apartment building, for example, the bugs show "an extremely high rate of inbreeding," Schal said. His team found that an entire population within an apartment building—such as were the cases in infested Jersey City, N.J., and Raleigh, N.C. buildings—was so genetically similar that it might have been founded by a single fertilized female. Bugs in the next generation then would have mated with one another, and so on, in a seemingly indefinite incestuous line.
Just how these and some other bugs can sustain this level of inbreeding and continue a healthy, bourgeoning population base remains unclear. In most species, such tight mating circles lead to genetic bottlenecks and mutations, which weaken a population. But in some insects, such as bedbugs and cockroaches, inbreeding seems to have become a perfectly safe form of reproduction.
In one Jersey City apartment building studied, the group even found a clue that the bugs prefer this arrangement. In this multi-unit building, two genetically distinct populations had infested several apartments each. But on one floor, one apartment had bedbugs from one genetic group, whereas the neighboring apartment had bugs from the other group. And the two populations showed no evidence of mixing, which suggests they might prefer their own gene pools, or even be incompatible with other groups.
Bedbugs can also cover a lot of ground—and quickly. In lab experiments, they have been shown to wander more than 2.5 meters in five minutes, noted Ken Haynes, of the University of Kentucky.
And once they have moved in, bedbugs are tough to stop. Females can live up to a year without imbibing so much as a drop of blood. So wrapping your belongings in plastic for a few weeks or going on vacation will hardly put a dent in their numbers. "They'll win," Vaidyanathan said. "They can hold out longer than we can."
The best strategy to head off a full-blown inbred infestation is still early detection, when they are easiest to excise.