Velez, I. D. | Search bioRxiv

bioRxiv2025

High genomic stability of wMel Wolbachia after introgression into three geographically distinct Aedes aegypti populations

The introgression of wMel Wolbachia into Aedes aegypti populations is being used for the biocontrol of arboviruses such as dengue and chikungunya in 15 countries to date. A wMel infection in Ae. aegypti both reduces the transmission of viruses by the mosquito and causes a reproductive manipulation that aids wMel introgression into naive populations. However, a critical concern is whether wMel could evolve over time, potentially diminishing these desired phenotypes. Here, we investigated the stability of the wMel genome in Ae. aegypti released for biocontrol in Colombia, Indonesia, and Vietnam. We sequenced the wMel genome at the start of releases and up to six years after wMel introgression into each population. Our study identifies very few genomic changes, suggesting the wMel genome is not rapidly evolving despite its release into three geographically different field sites and subsequent exposure to novel environments. These results align with previous wMel sequencing studies from Australia and provide strong evidence for the long-term genomic stability of wMel, reinforcing its potential as a reliable biocontrol tool against Ae. aegypti-transmitted arboviruses.

evolutionary biology↗

bioRxiv2024

Wolbachia introgression in Ae. aegypti is accompanied by variable loss - a multi-country assessment

The wMel and wAlbB strains of the bacterial endosymbiont Wolbachia are being introgressed into Aedes aegypti populations as a biocontrol method to reduce the transmission of medically important arboviruses. Successful introgression of Wolbachia relies on both persistence of Wolbachia throughout the host life cycle and a high fidelity of maternal transmission of Wolbachia between generations. wMel has been introgressed into field populations in 14 countries to date. Monitoring of field sites has shown that wMel prevalence can fluctuate substantially over time, prompting concerns this could lead to reduced efficacy of the biocontrol method. To explore the fidelity of wMel persistence and transmission, we developed molecular methods to measure the prevalence of Ae. aegypti negative for Wolbachia infection but carrying the "founder" mitochondrial haplotype of the single female first transinfected. As all released wMel-infected mosquitoes and any subsequent offspring will carry this founder mitochondrial haplotype, any mosquitoes with this mitochondrial haplotype and without wMel indicate that wMel was lost from this lineage at some point. We observed loss of wMel ranging from 0 to 20.4% measured at various time intervals after wMel-infected mosquito releases in five different countries. Despite some field sites showing Wolbachia loss, overall Wolbachia prevalence was sustained during the time periods studied. We then employed laboratory studies to explore factors that could contribute to the loss of wMel. Surprisingly, near-perfect maternal transmission was measured across laboratory conditions of early blood feeding, starvation, and salinity. Collectively, these findings underscore that although wMel 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.

ecology↗