Heat hardening enhances mosquito heat tolerance in a species-specific and assay-specific manner

Models predict that the distribution of many mosquito species will shift with climate change, but few incorporate adaptive capacity. Acclimation is one mechanism that allows mosquitoes previously exposed to sub-lethal stress to better tolerate subsequent stress. In this study we evaluated the heat tolerance of three vector mosquitoes, Aedes aegypti , Ae. notoscriptus and Culex quinquefasciatus, after prior exposure to heat hardening. Adults from all species were heat-hardened by exposure to 41 °C for 1 h, subsequently tested for (1) heat survival and knockdown responses following 1-h heat shocks across a range of temperatures up to the lethal limit, (2) ramping CTmax assays and (3) static temperature knockdown time assays. Females from all three species were more heat tolerant than males in the 1-h heat shock assays, but effects of sex were absent or inconsistent for CTmax and heat knockdown time assays. A beneficial impact of heat hardening on subsequent heat shock knockdown was evident in both sexes of all three species. However, hardening effects differed substantially for survival 24 h later, ranging from no effect of hardening in Cx. quinquefasciatus to a ∼1 °C increase in LT 50 in Ae. notoscriptus . In contrast, no effects of heat hardening were detected for CTmax or static knockdown time assays. An additional experiment in Ae. aegypti detected no benefits of parental heat shock exposure on the thermal tolerance of offspring. Our findings emphasize the need to consider effects of acclimation including heat hardening in models to predict the response of mosquitoes to climate warming. They also have implications for measuring thermal tolerance more generally, as sex and hardening effects depend on the type of assay used and trait measured.