Bed Bugs Can Bypass Pitfalls of Inbreeding, Studies Say
Finding means they can cause rapid infestation, may explain recent resurgence
TUESDAY, Dec. 6, 2011 (HealthDay News) -- Bed bugs appear to breed with their close relatives, an adaptation that not only ups their "yuck" factor but also enhances the tiny bloodsuckers' ability to thrive, two new studies find.
Entomologists from North Carolina State University did a genetic analysis of bed bugs taken from infested apartment buildings in North Carolina and New Jersey. Their analysis showed the bugs had low genetic diversity, meaning that close relatives had mated with one another.
In most species, breeding with close relatives means genetic mutations accumulate, and offspring are more likely to be sickly or infertile, which hurts the species over time, explained study author Coby Schal, a professor of entomology. Yet, inbreeding doesn't seem to bother bed bugs.
Just one "mated" female could be enough to start a nasty infestation, because her offspring will mate with each other, and so on. In the North Carolina building, for example, about one-quarter of about 90 apartments had bed bugs.
"Infestations are generally founded by just one female, and the fact is that the infestation can sweep through a building because the bed bugs are able to withstand inbreeding," Schal said. "We don't understand the genetic mechanism that allows them to do that, but it's not uncommon among insects associated with humans, especially those that don't fly, such as cockroaches."
In a second study, the researchers analyzed the genetic make up of bed bugs from 21 infestations in households from Maine to Florida, and also found evidence of inbreeding.
The research was to be presented Tuesday at the American Society of Tropical Medicine and Hygiene (ASTMH) annual meeting in Philadelphia.
After nearly vanishing by the 1950s, bed bugs now show up in homes, hotels and dorm rooms throughout the United States and the world, experts said. The explanation for their re-emergence isn't fully understood, but it's suspected that the bugs have developed a resistance to the pesticides used to kill them. Those pesticides include pyrethroids, commonly found in cans of insect spray, and DDT, which is banned in the United States but still used in other countries, Schal said.
A third study to be presented at the meeting, by researchers from University of Kentucky, found that killing resistant bed bugs takes 10,000 times more pyrethroid insecticide than destroying a strain of bed bugs never exposed to the insecticide.
The good news is bed bugs are not known to carry disease, although some people can have allergic reactions, said Dr. Peter Hotez, president of ASTMH. "While it's an annoyance, there shouldn't be cause for alarm," he said.
More research is needed to confirm the inbreeding findings and the theory that pesticide resistance is to blame for the resurgence, Hotez said. But, "if you have insecticide resistance and inbreeding, those two findings suggest we could be looking at larger bed bug problem in the coming months and years," Hotez said.
Though often associated with unsanitary conditions, bed bugs aren't attracted to dirt, experts said. They are more likely to be found in poorer buildings, but that's likely because of lack of resources to pay for expensive extermination, Schal said.
Fumigation with pesticides can eradicate bed bugs from a building, but it may take multiple efforts because of resistance, Schal said. Another technique involves sealing off a building and heating the interior to between 120 and 130 degrees, which kills the bugs and their eggs. But that can be costly and requires specialized equipment, he said.
Adult bed bugs are reddish-brown and oval-shaped. Before feeding, the adult bed bug is relatively flat. After feeding, it becomes a darker red.
During the day, they hide in cracks and crevices, box springs and mattress seams. At night, they come out to feed. "If they're hungry, they will bite pets, but they much prefer humans," Schal said.
Bed bug mating -- known as "traumatic insemination" -- is "quite an amazing story," Schal said. Males pierce the body of a female and insert sperm into her bloodstream, where it seeks out a sperm storage organ. She can keep it there for weeks before using it to fertilize her eggs, which she'll lay at a rate of about one a day.
"It doesn't matter if they are brother and sister, or mother and son, they can mate and start a whole new population," he said.
In other research to be presented at the meeting, researchers said they're learning more about bed bugs' "alarm pheromones," which, when sensed by the bugs, cause them to run away. Presumably, alarm pheromones could be used to send bed bugs scurrying toward insecticides, researchers said.
Because the research was presented at a medical meeting, the conclusions should be viewed as preliminary until published in a peer-reviewed journal.
The U.S. Environmental Protection Agency has more on getting rid of bed bugs.