Use of Wolbachia to interfere with vector capacity in Aedes spp. mosquitoes: establishment of new Wolbachia-host associations for the control of vector-borne diseases

Wolbachia are intracellular bacteria able to manipulate host insect reproduction through cytoplasmic incompatibility (CI) and several strain can interfere with virus transmission. These strains vary in their impact on host fitness, showing varying levels of adaptability; they can become pathogenic in some cases or gradually disappear. In this study, an aposymbiotic line of Ae. albopictus was successfully transinfected with the wMel strain, resulting in the SwMel1 line. The new transinfected line initially exhibited transient stability, with the infection becoming fixed in the population by the second generation. However, this stability was short-lived as transmission rates and infection levels declined from the ninth generation onwards, indicating challenges in the bacterium's adaptation to the new intracellular environment. Characterization studies revealed significant fitness costs on female parameters such as fecundity, fertility, and survival. The males of the new line initially induced high levels of CI (around 90%) in all tested crosses but showed a significant decline from the ninth generation onwards. Tissue distribution analysis confirmed the presence of Wolbachia infection in various body tissues, with a notable prevalence in the ovaries, but exhibiting a higher somatic distribution rate compared to other known artificially generated infections (i.e., wPip). The impact of high temperatures on bacterial density was also evaluated, revealing that SwMel1 females were particularly sensitive to prolonged exposure to elevated temperatures. Overall, this research underscores the complexities involved in using transinfected mosquito lines for pest management, emphasizing the importance of understanding symbiotic dynamics and their implications for both host and bacterial fitness.