141. The mosquito Aedes aegypti is largely confined to tropical and subtropical regions but its 15 range has recently been spreading to colder climates. As insect biogeography is closely 16 tied to environmental temperature, understanding the limits of Ae. aegypti thermal 17 tolerance and their capacity for phenotypic plasticity is important in predicting the spread 18 of this species. 19 2. In this study we report on the chill coma onset and recovery, as well as low temperature 20 survival phenotypes of larvae and adults of Aedes aegypti that developed or were 21 acclimated to 15°C (cold) or 25°C (warm). 22 3. Developmental cold acclimation did not affect chill coma onset of larvae but substantially 23 reduced chill coma onset temperatures in adults. Chill coma recovery time was affected 24 by both temperature and the duration of exposure, and developmental and adult 25 acclimation both strongly mitigated these effects and increased rates of survival following 26 prolonged chilling.27 4. Female adults were far less likely to take a blood meal when cold acclimated and simply 28 exposing females to blood (without feeding) attenuated some of the beneficial effects of 29 cold acclimation on chill coma recovery time. 30 5. Lastly, larvae suffered from hemolymph hyperkalemia when chilled, but development in 31 the cold attenuated the imbalance, which suggests that acclimation can prevent cold-32 induced ionoregulatory collapse in this species. 33 6. Our results demonstrate that Aedes aegypti larvae and adults have the capacity to 34 acclimate to cold temperatures and do so at least in part by better maintaining ion balance 35 in the cold. This ability for cold acclimation may facilitate the spread of this species to 36 higher latitudes, particularly in an era of climate change.37 38 Low temperatures adversely affect life history traits throughout the Ae. aegypti life cycle, 61 including development rate, reproductive success, and survival (Carrington, Armijos, 62

The mosquito Aedes aegypti is largely confined to tropical and subtropical regions, but its range has recently been spreading to colder climates. As insect biogeography is tied to environmental temperature, understanding the limits of Ae. aegypti thermal tolerance and their capacity for phenotypic plasticity is important in predicting the spread of this species. In this study we report on the chill coma onset (CCO) and recovery time (CCRT), as well as low temperature survival phenotypes of larvae and adults of Ae. aegypti that developed or were acclimated to 15°C (cold) or 25°C (warm). Cold acclimation did not affect CCO temperatures of larvae but substantially reduced CCO in adults. Temperature and the duration of exposure both affected CCRT, and cold acclimation both strongly mitigated these effects and increased rates of survival following prolonged chilling. Female adults were far less likely to take a blood meal when cold acclimated, and exposing females to blood (without feeding) attenuated some of the beneficial effects of cold acclimation on CCRT. Lastly, larvae suffered from hemolymph hyperkalemia when chilled, but cold acclimation attenuated the imbalance. Our results demonstrate that Aedes aegypti larvae and adults have the capacity to acclimate to low temperatures, and do so at least in part by better maintaining ion balance in the cold. This ability for cold acclimation may facilitate the spread of this species to higher latitudes, particularly in an era of climate change.