Parental exposure to variable saturation deficit shapes the survival and thermotolerance of Aedes aegypti eggs

Vector insects, especially mosquitoes, display remarkable survival across ecological gradients. Central to this resilience is the egg stage, which must withstand fluctuating moisture and temperature conditions for extended periods. This study investigates how the parental stage, exposed to variable levels of saturation deficit, shapes reproductive output and subsequent egg thermal tolerance in Aedes aegypti. Using four environmental regimes, i.e., continuous low saturation deficit (LSD), continuous high saturation deficit (HSD), LSD-to-HSD, and HSD-to-LSD, we assessed egg output, egg hatching success, egg thermotolerance, and egg nutrient composition across three Ae. aegypti populations. The pupae were reared in water cups in either continuous LSD or continuous HSD chambers, and eight days of post-emergence, mosquitoes were blood-fed before subset groups were transferred to the opposite hydration environment. Our results show that oviposition timing and egg production are significantly affected by the hydration environment experienced by the parental generation. While the LSD, HSD, and HSD-to-LSD groups exhibited a consistent oviposition peak beginning four days post-blood feeding, the LSD-to-HSD group showed delayed egg production. Egg output was significantly reduced in the HSD and LSD-to-HSD treatments. The eggs from the LSD-to-HSD groups showed significantly higher thermotolerance than those from the other groups across all three populations. The nutritional composition showed increased glycogen levels in eggs when parents were exposed to LSD conditions before blood feeding. By integrating physiological and ecological metrics, such as hatching rates and thermal stress resilience, we demonstrate how parental environments shape subsequent egg performance, highlighting adaptive responses that enable Ae. aegypti persistence under periods of thermal and dehydration stress.