Wolbachia in mosquitoes from the Central Valley of California, USA

Authors: TORRES, RYAN - University Of California; HERNANDEZ, EUNIS - University Of California; FLORES, VALERIA - University Of California; Ramirez, Jose; JOYCE, ANDREA - University Of California

Submitted to: Parasites & Vectors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/24/2020
Publication Date: 11/10/2020
Citation: Torres, R., Hernandez, E., Flores, V., Ramirez, J.L., Joyce, A.L. 2020. Wolbachia in mosquitoes from the Central Valley of California, USA. Parasites & Vectors. 13. Article 558. https://doi.org/10.1186/s13071-020-04429-z.
DOI: https://doi.org/10.1186/s13071-020-04429-z

Interpretive Summary: Wolbachia is a bacterium that infects a wide array of insects, including mosquitoes. Lately, Wolbachia has been used in vector control programs where it can be used to reduce the mosquito populations or make the mosquito less able to transmit pathogens that affect human health. Not all mosquito species carry Wolbachia and their identification in diverse mosquito species is crucial for the design of future Wolbachia-based mosquito control applications. This study looked at the presence/absence of Wolbachia in mosquitoes from Merced County in the Central Valley of California and reports for the first time Wolbachia in five mosquito species that were previously unknown. This study provides important information that can be used to inform potential vector control applications.

Technical Abstract: Background: Wolbachia bacteria are widely distributed throughout terrestrial arthropod species. These bacteria can manipulate reproduction and influence the vector competence of their hosts. Recently, Wolbachia have been integrated into vector control programs for mosquito management. A number of subgroups and strains exist for Wolbachia, and they have yet to be characterized for many mosquito species. In this study, we examined Wolbachia prevalence and their phylogenetic relationship to other Wolbachia, using mosquitoes collected in Merced County in the Central Valley of California. Methods: Adult mosquitoes were collected from 85 sites in Merced County, California in 2017 and 2018. Traditional and quantitative PCR were used to investigate the presence or absence and the density of Wolbachia, using Wolbachia-specific 16S rRNA and Wolbachia-surface protein (wsp) genes. The supergroup of Wolbachia was determined, and Multi Locus Sequence Typing (MLST) by sequencing five housekeeping genes (coxA, gatB, ftsZ, hcpA, and fbpA) was used to determine Wolbachia supergroup and strain. Results: Over 7100 mosquitoes of twelve species were collected; Aedes melanimon, Aedes nigromaculis, Aedes vexans, Aedes aegypti, Culex pipiens, Culex stigmatosoma, Culex tarsalis, Anopheles franciscanus, Anopheles freeborni, Anopheles punctipennis, Culiseta incidens, and Culiseta inornata. Eight showed evidence of Wolbachia-infection. This study is the first to report Wolbachia in five of these species (Ae. melanimon, Cx. stigmatosoma, Cx. tarsalis, Cs. incidens, and Cs. inornata). Cx. pipiens and Cx. stigmatosoma had a high frequency and density of Wolbachia infection, which grouped into supergroup B; Cs. inornata clustered with supergroup A. MLST comparisons identified Cx. pipiens and Cx. stigmatosoma as wPip strain type 9 supergroup B. Seven species had moderate to low (<14%) frequencies of infection. Three species were negative, An. franciscanus, An. freeborni, and Ae. aegypti. Conclusions: New records of Wolbachia infections were found in mosquitoes from Merced County, California. Cx. stigmatosoma and Cs. inornata were new records for Wolbachia-infection and grouped into supergroup B and A, respectively. Other species with Wolbachia infections occurred with low frequency and low density infections. Evidence of natural Wolbachia-infections can be used to inform potential vector control applications. Future study of natural Wolbachia-infections within Cx. stigmatosoma and Culiseta inornata in California and through the range of these species could provide information about the distribution of Wolbachia infections, and investigate whether Wolbachia-infections in Cx. stigmatosoma and Culiseta inornata modulate vector competence.