Quality control of long-term mass-reared Aedes albopictus for population suppression

The endosymbiotic bacterium Wolbachia is being developed as a tool to suppress mosquito populations and their transmitted pathogens, with successful field trials in multiple countries having resulted in efforts to scale up the capacity to mass-produce mosquitoes for release. However, major challenges exist to achieving this goal, including concerns that mass-reared mosquitoes will adapt to laboratory conditions during long-term maintenance and experience inbreeding depression, resulting in poor performance of the released mosquitoes in the field. Here, we assessed the performance of the Aedes albopictus HC line infected with a triple-strain Wolbachia after mass-rearing at scaled-up densities of up to 15 million mosquitoes per week for over 50 generations. In comparison with the wild-type GUA line, the HC mosquitoes had desirable characteristics for mass-rearing and release, including robust male mating competitiveness, high female reproductive capacity, reduced vector competence for dengue virus, and increased Wolbachia density. Although the larval survival rate of the HC and GUA lines was similar, the HC larvae developed significantly faster, possibly because of up-regulation of the molting hormone 20-hydroxyecdysone-related gene E75 in the HC larvae. Our results indicate that over many generations mass-reared mosquito lines can retain their quality if large effective population sizes with sufficient genetic heterogeneity are maintained under optimized rearing conditions and demonstrate the long-term feasibility of deploying Wolbachia-based approaches for area-wide management of mosquito vectors for disease control.