This adult female bed bug specimen collected in a home in Heredia, Costa Rica, in 2017 (along with 24 others, both male and female adults as well as nymphs) was confirmed to be of the species Cimex lectularius by researchers at the University of Costa Rica, who used both morphological and molecular analysis for the identification. The tropical bed bug (Cimex hemipterus) was last spotted in Costa Rica in the late 1990s, and the discovery of C. lectularius marks the first-ever known report of temperate-zone bed bugs there. (Image originally published in Cambronero-Heinrichs et al 2020, Journal of Medical Entomology)
By Andrew Porterfield
The near-eradication of bed bugs (Cimex lectularius in temperate climes, C. hemipterus in the tropics) as human pests was a 20th-century success story. Once a plague of blood-feeding insects with a history reaching back to at least to ancient Egypt, populations of Cimex have rebounded worldwide over the past 10 years, possibly because of insecticide resistance, inadequate controls, and increased international travel.
One area of the world that appeared to have escaped this resurgence, though, was Central America. Even in the past 10 years, the temperate C. lectularius was reported in Canada, the United States, Venezuela, Peru, Argentina and Chile, while only one report in Central America was noted in Nicaragua (the species wasn’t known). Previous reports from Nicaragua, Panama and Costa Rica did note the presence of the tropical bed bug (C. hemipterus), though no bed bugs of any species were reported in Costa Rica for 20 years.
That is, until now. A research team from the University of Costa Rica has used a number of molecular methods to positively identify bed bugs in that country for the first time in decades. Moreover, the species was C. lectularius and was genetically closest to strains of C. lectularius originating from China. The team’s findings were published this month in the Journal of Medical Entomology.
Microbiology researcher Juan Carlos Cambronero-Heinrichs and his colleagues at the University of Costa Rica (UCR) obtained the bed bugs from a bed in an apartment in Heredia, a town just north of the Costa Rican capital of San Jose, in 2017.
“The case reported in the article came to us thanks to the pest management company that initially dealt with the infestation,” says Cambronero-Heinrichs. “Laura Sánchez, co-author of this paper and a biology student of UCR at the time, visited the house, interviewed the owners, collaborated with the company, collected samples, and morphologically identified the specimens. The people living in the house reported being very affected by the bites. Later, Laura sought the help of our Medical Entomology laboratory in the School of Microbiology to confirm the identification, so we carried out molecular analyses.
“We immediately knew this case was very important,” Cambronero-Heinrichs continues, “because our laboratory maintains a collection of arthropods of medical importance that receives samples every year from different areas of the country, and there had been no reports of bedbugs for decades. In fact, thanks to this collection we know that the specimens we have from infestations before the 1980s correspond to Cimex hemipterus and not Cimex lectularius, as in this report.”
The insects were identified according to their morphology, and DNA was extracted from one nymph. A polymerase chain reaction (PCR) test was used to amplify fragments of two key mitochondrial genes: cytochrome oxidase subunit I (COI) gene, and the 16S rRNA gene. These genes are often used for determining relationships between species members because they are conserved more than other genes.
These DNA segments were edited and identified by comparing with other publicly available DNA sequences using the Basic Local Alignment Search Tool (BLAST), an online database and comparison method that offers a “best match” to organismal DNA worldwide. The BLAST tool relies heavily on the GenBank database, a global collection of DNA sequences.
In total, 25 bed bugs were identified as C. lectularius, based on morphological characteristics that included a pronotum plate (covering the dorsal thorax) with a deep anterior margin. COI and 16S RNA sequencing confirmed the species. These sequences showed their highest similarity, more than 98 percent, to C. lectularius DNA sequences from China. However, no C. lectularius sequences in the GenBank database were obtained from Latin American countries, making it impossible to compare genetic sequences accurately from neighboring countries.
“Results show that C. lectularius is present in Costa Rica,” the researchers write, marking the first confirmed report of a bed bug in Costa Rica in more than 20 years, and the first report of the temperature-zone bed bug ever.
“It is possible that the recent introduction of C. lectularius is related to tourism or immigration,” the authors add. “Given that adult and nymphs of bed bugs or their eggs can be easily transported in packed clothes, furniture, or other fomites, the ectoparasite resurgence around the world has been associated with the increase in international travel.”
Left to right, Ólger Calderon, Juan Carlos Cambronero-Heinrichs, Laura Sánchez, and Adriana Troyo are the team of researchers who have positively identify bed bugs in Costa Rica for the first time in decades. Sánchez is a student and Calderon, Cambronero-Heinrichs, and Troyo are faculty researchers in the department of microbiology at the University of Costa Rica. (Photo courtesy of Juan Carlos Cambronero-Heinrichs)
The discovery of C. lectularius could have a significant impact on tourism, currently Costa Rica’s most valuable industry. Infestations can result in bad reputations for hotels and can also result in significant cost increases for controlling the parasitic insects. While bedbugs are not commonly associated with disease transmission, their bites do draw blood and can cause skin reactions and sometimes more severe allergic reactions.
Cimex lectularius has shown significant resistance to pyrethroid insecticides, and government and private pesticide control professionals should consider this when working out management strategies, the authors note.
Editor’s note: This article was updated February 3, 2020, to include comment from Juan Carlos Cambronero-Heinrichs and to add the photo of his research team.
Andrew Porterfield is a writer, editor, and communications consultant for academic institutions, companies, and nonprofits in the life sciences. He writes frequently about agriculture issues for the Genetic Literacy Project. He is based in Camarillo, California. Follow him on Twitter at @AMPorterfield or visit his Facebook page.