Stability of the wMel Wolbachia Infection following Invasion into Aedes aegypti Populations

The wMel infection of Drosophila melanogaster was successfully transferred into Aedes aegypti mosquitoes where it has the potential to suppress dengue and other arboviruses. The infection was subsequently spread into two natural populations at Yorkeys Knob and Gordonvale near Cairns, Queensland in 2011. Here we report on the stability of the infection following introduction and we characterize factors influencing the ongoing dynamics of the infection in these two populations. While the Wolbachia infection always remained high and near fixation in both locations, there was a persistent low frequency of uninfected mosquitoes. These uninfected mosquitoes showed weak spatial structure at both release sites although there was some clustering around two areas in Gordonvale. Infected females from both locations showed perfect maternal transmission consistent with patterns previously established pre-release in laboratory tests. After >2 years under field conditions, the infection continued to show complete cytoplasmic incompatibility across multiple gonotrophic cycles but persistent deleterious fitness effects, suggesting that host effects were stable over time. These results point to the stability of Wolbachia infections and their impact on hosts following local invasion, and also highlight the continued persistence of uninfected individuals at a low frequency most likely due to immigration.Author Summary: The wMel infection is a Wolbachia infection introduced into Aedes aegypti mosquito populations; wMel can provide potential suppression of dengue if the infection persists in populations. We show that the infection has persisted at a high frequency since its initial introduction into two natural populations in North Queensland, Australia. The infection, which is inherited through females, appears perfectly transmitted to offspring in the field. It has continued to produce a high level of incompatibility when infected males are mated with uninfected females; these females are likely to enter populations at a low frequency as migrants. These features ensure that the infection will stay at a high frequency in populations, but costs prevent its rapid spread.