An elusive endosymbiont: Does <i>Wolbachia</i> occur naturally in <i>Aedes aegypti</i> ?

Abstract

<i>Wolbachia</i> are maternally inherited endosymbiotic bacteria found within many insect species. <i>Aedes</i> mosquitoes experimentally infected with <i>Wolbachia</i> are being released into the field for <i>Aedes-</i>borne disease control. These <i>Wolbachia</i> infections induce cytoplasmic incompatibility which is used to suppress populations through incompatible matings or replace populations through the reproductive advantage provided by this mechanism. However, the presence of naturally occurring <i>Wolbachia</i> in target populations could interfere with both population replacement and suppression programs depending on the compatibility patterns between strains. <i>Aedes aegypti</i> were thought to not harbor <i>Wolbachia</i> naturally but several recent studies have detected <i>Wolbachia</i> in natural populations of this mosquito. We therefore review the evidence for natural <i>Wolbachia</i> infections in <i>A. aegypti</i> to date and discuss limitations of these studies. We draw on research from other mosquito species to outline the potential implications of natural <i>Wolbachia</i> infections in <i>A. aegypti</i> for disease control. To validate previous reports, we obtained a laboratory population of <i>A. aegypti</i> from New Mexico, USA, that harbors a natural <i>Wolbachia</i> infection, and we conducted field surveys in Kuala Lumpur, Malaysia, where a natural <i>Wolbachia</i> infection has also been reported. However, we were unable to detect <i>Wolbachia</i> in both the laboratory and field populations. Because the presence of naturally occurring <i>Wolbachia</i> in <i>A. aegypti</i> could have profound implications for <i>Wolbachia</i>-based disease control programs, it is important to continue to accurately assess the <i>Wolbachia</i> status of target <i>Aedes</i> populations.