A wMel Wolbachia variant in Aedes aegypti from field-collected Drosophila melanogaster with increased phenotypic stability under heat stress

Population replacement strategies involving the wMel strain of Wolbachia are being used widely to control mosquito-borne diseases. However, these strategies may be influenced by temperature because wMel is vulnerable to heat. wMel infections in Drosophila melanogaster are genetically diverse, but few transinfections of wMel variants have been generated in Aedes aegypti. Here we successfully transferred a wMel variant (termed wMelM) originating from a field-collected D. melanogaster into Ae. aegypti. We compared the genome sequence of wMelM from the original D. melanogaster donor to that of wMelM from Aedes aegypti at multiple generations post-transinfection, and found that the genome sequence remained stable following transfer to the new mosquito host. The new wMelM variant (clade I) is genetically distinct from the original wMel transinfection (clade III). We compared wMelM with wMel in its effects on host fitness, temperature tolerance, Wolbachia density, vector competence, cytoplasmic incompatibility and maternal transmission under heat stress in a controlled background. wMelM showed a higher heat tolerance than wMel, likely due to higher overall densities within the mosquito. Both wMel variants had minimal host fitness costs, complete cytoplasmic incompatibility and maternal transmission, and dengue virus blocking under laboratory conditions. Our results highlight phenotypic differences between Wolbachia variants and wMelM shows potential as an alternative strain in areas with strong seasonal temperature fluctuations.