strain MelM disrupts egg retention by females prevented from ovipositing.

mosquitoes are well adapted to dry climates and can retain their eggs for extended periods in the absence of suitable habitat. strains transferred from other insects to mosquitoes can be released to combat dengue transmission by blocking virus replication and spreading through populations, but host fitness costs imposed by , particularly under some environments, can impede spread. We, therefore, assessed the impact of two strains being released for dengue control (AlbB and MelM) on fecundity and egg viability following extended egg retention (up to 24 days) under laboratory conditions. Egg viability following retention decreased to a greater extent in females carrying MelM compared to uninfected or AlbB females. Fertility fully recovered in uninfected females following a second blood meal after laying retained eggs, while MelM females experienced only partial recovery. Effects of MelM on egg retention were similar regardless of whether females were crossed to uninfected or MelM males, suggesting that fitness costs were triggered by presence in females. The fecundity and hatch proportions of eggs of MelM females declined with age, regardless of whether females used stored sperm or were recently inseminated. Costs of some strains during egg retention may affect the invasion and persistence of in release sites where larval habitats are scarce and/or intermittent.IMPORTANCE mosquito releases are expanding around the world with substantial impacts on dengue transmission. Releases have succeeded in many locations, but the establishment of has been challenging in some environments, and the factors contributing to this outcome remain unresolved. Here, we explore the effects of on a novel trait, egg retention, which is likely to be important for the persistence of mosquito populations in locations with intermittent rainfall. We find substantial impacts of the strain MelM on the quality of retained eggs but not the AlbB strain. This cost is driven by the infection status of the female and can partially recover following a second blood meal. The results of our study may help to explain the difficulty in establishing strains at some field release sites and emphasize the need to characterize phenotypes across a variety of traits and strains.