Wolbachiaintrogression inAe. aegyptiis accompanied by variable loss – a multi-country assessment

Abstract

AbstractThewMel andwAlbB strains of the bacterial endosymbiontWolbachiaare being introgressed intoAedes aegyptipopulations as a biocontrol method to reduce the transmission of medically important arboviruses. Successful introgression ofWolbachiarelies on both persistence ofWolbachiathroughout the host life cycle and a high fidelity of maternal transmission ofWolbachiabetween generations.wMel has been introgressed into field populations in 14 countries to date. Monitoring of field sites has shown thatwMel prevalence can fluctuate substantially over time, prompting concerns this could lead to reduced efficacy of the biocontrol method. To explore the fidelity ofwMel persistence and transmission, we developed molecular methods to measure the prevalence ofAe. aegyptinegative forWolbachiainfection but carrying the “founder” mitochondrial haplotype of the single female first transinfected. As all releasedwMel-infected mosquitoes and any subsequent offspring will carry this founder mitochondrial haplotype, any mosquitoes with this mitochondrial haplotype and withoutwMel indicate thatwMel was lost from this lineage at some point. We observed loss ofwMel ranging from 0 to 20.4% measured at various time intervals afterwMel-infected mosquito releases in five different countries. Despite some field sites showingWolbachialoss, overallWolbachiaprevalence was sustained during the time periods studied. We then employed laboratory studies to explore factors that could contribute to the loss ofwMel. Surprisingly, near-perfect maternal transmission was measured across laboratory conditions of early blood feeding, starvation, and salinity. Collectively, these findings underscore that althoughwMel transmission can be imperfect it does not necessarily undermine population-level establishment, providing encouragement that the intervention will be robust in most dengue-endemic environments.