Multiple mechanisms for resisting pesticides and mitigating the effects of rough sexual insemination practices are just a few of the key findings from the completed genetic blueprint of the bedbug - the parasitic pest that has experienced a global resurgence during the past two decades.
In a paper published in Nature Communications, researchers tease apart the genomic framework of Cimex lectularius, the common bedbug, and report some of the unique features leading to some of the insect's most reviled and bedeviling characteristics. The findings will lead to further study of some of these attributes to learn more about how to disarm the ubiquitous pest, says Coby Schal, Blanton J. Whitmire Distinguished Professor of Entomology at NC State and a co-leader of the bedbug genome sequencing project.
"This paper expands to the genomic level some of the things we've known for a long time," Schal said. "We've known, for example, that bedbugs are resistant to insecticides for some time. The genome sequence shows genes that encode enzymes and other proteins that the bedbug can use to fight insecticides, whether by degrading them or by preventing them from penetrating its body."
The genome sequence also shows genes that encode whole sets of proteins that reduce the traumatic effects of bedbug copulation. Male bedbugs will try to copulate with just about every bedbug 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.
Some bacterial genes have also been integrated into the bedbug genome, Schal says. In this lateral gene transfer, one particular insect parasite, a bacterium called Wolbachia, has a special relationship with the pests: Wolbachia provide something that blood meals do not - a vitamin B complex that helps bedbugs live and thrive.
"In this case of mutualism, genomic sequences from Wolbachia are present in the bedbug genome," Schal said. "We don't know if the bacterium is co-opting the bedbug or if the bedbug 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 bedbug, such as those involved in B vitamin metabolism, were incorporated into the bedbug genome."
Another important finding shows that the bedbug 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 bedbugs have no need for sugary meals, Schal says, so evolution has eliminated their sugar receptors.
The bedbug genome sequence also sheds light on the mechanisms behind some of the effects of the bedbug's bite.
"Bedbug saliva contains a local anesthetic with a number of proteins that prevent coagulation," Schal said. "This allows the bedbug to bite stealthily without being detected."
Bedbugs also have incredible diuretic systems that allow the pests to shed water. Bedbugs can expand their bodies by 100 to even 200 percent while eating a blood meal; much of that expansion goes to water in the blood.
"Bedbugs must be able to shed that water while retaining the blood's nutrients," Schal said.
Researchers from the Baylor College of Medicine and the University of Cincinnati are lead authors on the paper. Funding for Schal's portion of the work came from the U.S. Department of Housing and Urban Development (award NCHHU-0017-13), the Alfred P. Sloan Foundation (award 2013-5-35 MBE), the National Science Foundation (award IOS-1052238) and NC State's Blanton J. Whitmire endowment.
Note to editors: An abstract of the paper follows.
"Unique features of a global human ectoparasite identified through sequencing of the bed bug genome"
Authors: Joshua Benoit, University of Cincinnati; Coby Schal, North Carolina State University; Stephen Richards, Baylor College of Medicine; et al.
Published: Online Feb. 2, 2016, in Nature Communications
Abstract: The bed bug, Cimex lectularius, has re-established itself as a ubiquitous human ectoparasite throughout much of the world during the past two decades. This global resurgence is likely linked to increased international travel and commerce in addition to widespread insecticide resistance. Analyses of the C. lectularius sequenced genome (650Mb) 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. In addition, we document the presence of multiple putative lateral gene transfer events. Genome sequencing and annotation establish a solid foundation for future research on mechanisms of insecticide resistance, human-bed bug and symbiont-bed bug associations, and unique features of bed bug biology that contribute to the unprecedented success of C. lectularius as a human ectoparasite.
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