by Elizabeth Pennisi
Scientists have recently made progress detailing the evolutionary histories of insects like stink bugs, kissing bugs, and assassin bugs, says Christiane Weirauch, a systematic entomologist at the University of California, Riverside, who was not involved in the new study. But “with bedbugs we have not done too well.” Many species are parasites of bats, and researchers had long assumed that these mammals were their first victims. But bat bedbug species are hard to collect: Many are never found except in the depths of caves where bats roost. “You don’t know how difficult it is to get some of these bedbug species,” Weirauch laments.
That inaccessibility didn’t stop Klaus Reinhardt, whose interest in bedbugs has led him to write two treatises about the cultural history of bedbugs. For the bedbug family tree study, this entomologist at Dresden University of Technology in Germany and colleagues got some of their specimens from museums and other researchers. But the rest they chased down in areas plagued by civil war, and in hot, dark caves, where they traipsed through knee-deep guano—only after dealing with all the red tape needed to get permission to work on endangered bats. Once they had collected thousands of bugs, they sequenced and compared DNA from 34 species to build the family tree.
They used a 100-million-year-old fossil and estimated mutation rates to calculate when bedbugs first appeared and when they diversified. That work revealed that bedbugs “existed long before any records of bats,” says Thomas Lilley, an ecophysiologist at the Finnish Museum of Natural History in Helsinki. The oldest known bat fossil is just 64 million years old, and, according to the new study, bedbugs date back 115 million years, to the time of the dinosaurs, Reinhardt and his colleagues report today in Current Biology. “This is something that people have suspected, but it’s really nice to have it in black and white,” Weirauch says. Also, it now appears that those first bedbugs evolved from an ancestral bug that was already a blood sucker—some researchers thought blood meals came later, after bedbugs had already split from their ancestors.
The new family tree also upends ideas about bedbugs and humans. Two species of the insect—Cimex lectularius and the tropical C. hemipterus—typically bite people. Previously, researchers proposed that the two types arose from a common ancestor and diverged about 1.6 million years ago when Homo sapiens split off from an ancient human line, H. erectus. But the new study indicates the two bedbugs went their separate ways 47 million years ago, meaning both must have independently shifted to a human diet.
Since then, one or two other bedbug species have switched to human hosts, Reinhardt says. For example, his research on Hopi legends has convinced him that a bedbug known to infect eagles also started to feed on humans. And the human-loving bedbug Leptocimex boueti, which also enjoys bat blood and likely had that mammal as its first host, may have switched to people as global guano mining increased. Together, the evidence suggests “a new species of bedbug conquers humans about every half a million years,” Reinhardt says. Given the ever-growing contact among people, livestock, and wildlife, “It may not even take half a million years,” for another bedbug to start sucking human blood, he adds.
Bedbugs’ host-switching success suggests they are incredibly good at adapting to new situations, notes Coby Schal, a behavioral ecologist at North Carolina State University in Raleigh, who was not involved with work. “Bedbug populations rapidly adapted to global travel, other changes in human behavior, and [insecticides].” And, he predicts, they will continue to do so.