A large multinational team of scientists has successfully sequenced the whole genome of the common bed bug (Cimex lectularius), uncovering several traits that could reveal why this human ectoparasite is so resistant to pesticides.
A close-up of the common bed bug (Cimex lectularius). Image credit: Armed Forces Pest Management Bureau.
“Analyses of the bed bug sequenced genome (650 Mb) and 14,220 predicted protein-coding genes provide a comprehensive representation of genes that are linked to traumatic insemination, a reduced chemosensory repertoire of genes related to obligate hematophagy, host-symbiont interactions, and several mechanisms of insecticide resistance,” the researchers wrote in a paper in the journal Nature Communications. “In addition, we document the presence of multiple putative lateral gene transfer events.”
The bed bug genome sequence shows genes that encode enzymes and other proteins that the bed bug can use to fight insecticides, whether by degrading them or by preventing them from penetrating its body.
It also reveals genes that encode whole sets of proteins that reduce the traumatic effects of copulation.
“Male bed bugs will try to copulate with just about every bed bug that moves, including babies and other males. Males inject a sickle-shaped appendage into a V-shaped area of the female’s abdomen called the spermalege. To counter this damaging process, females produce the protein resilin, which makes the spermalege firmer yet more flexible to adapt to harsh copulation attempts,” the scientists said.
“Some bacterial genes have also been integrated into the bed bug genome,” said co-author Prof. Coby Schal, of North Carolina State University.
“We picked up more than 800 putative lateral gene transfer bits,” added lead author Dr. Joshua Benoit, from the University of Cincinnati.
“That included Wolbachia bacteria, a common reproductive parasite, and Arsenophonus.”
According to the scientists, Wolbachia has a special relationship with the pests.
“Wolbachia provide something that blood meals do not – a vitamin B complex that helps bed bugs live and thrive,” Prof. Schal said.
“In this case of mutualism, genomic sequences from Wolbachia are present in the bed bug genome.”
“We don’t know if the bacterium is co-opting the bed bug or if the bed bug is co-opting the bacterium.”
“Very few of these bacterial genes are functional and we don’t know what proteins they are producing. But it would be fascinating if bacterial genes that are useful to the bed bug, such as those involved in B vitamin metabolism, were incorporated into the bed bug genome.”
Another important finding shows that the bed bug genome contains no sugar receptors – supporting the prevailing hypothesis that insects feeding exclusively on blood no longer need to detect sugar in their food.
“Unlike mosquitoes – which feed, depending on gender, upon both blood and floral nectar sugars – obligate blood-feeders like bed bugs have no need for sugary meals, so evolution has eliminated their sugar receptors,” Prof. Schal explained.
The bed bug genome sequence also sheds light on the mechanisms behind some of the effects of the bed bug’s bite.
“Bed bug saliva contains a local anesthetic with a number of proteins that prevent coagulation. This allows the insect to bite stealthily without being detected,” Prof. Schal said.
Bed bugs also have incredible diuretic systems that allow the pests to shed water. They can expand their bodies by 100% to even 200% while eating a blood meal; much of that expansion goes to water in the blood.
“Bed bugs must be able to shed that water while retaining the blood’s nutrients,” Prof. Schal said.
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Joshua B. Benoit et al. 2016. Unique features of a global human ectoparasite identified through sequencing of the bed bug genome. Nature Communications 7, article number: 10165; doi: 10.1038/ncomms10165
