As in our study, southern populations of the pitcher plant mosquito have higher growth rates and a lower cold resistance than northern populations. Further, lowland populations of the copper butterfly have higher growth rates and reduced cold resistance. Finally, faster growing plant species have higher frost damage. Cold resistance, as measured by shorter chill coma recovery times, was higher in the northern populations and higher at the lowest rearing temperature. This is in line with studies along latitudinal gradients in other insects, which considered this latitudinal pattern as a direct result of geographic differences in thermal selection. Also in our study system thermal selection for increased cold resistance is likely higher in the northern populations. Yet, the observation that latitudinal differences in cold resistance were not significant anymore when growth rate was added to the model indicates growth rate differences are contributing to the latitudinal differences in cold Nialamide resistance. We therefore hypothesize that the latitudinal pattern in cold resistance in our study system may not be entirely explained by thermal selection per se but also by the higher growth rates at lower latitudes. While there was some indication that the physiological cost of rapid growth in terms of reduced cold resistance was mediated through reduced Hsp70 levels there was no support for this at the individual level. Treatment groups with higher growth rates and longer recovery times, i.e. southern populations and animals reared at higher temperatures, indeed had lower Hsp70 levels, and at the individual level faster growing animals had lower Hsp70 levels. Yet, individual variation in Hsp70 levels did not explain variation in recovery times when taking into account the treatment effects. A reason for this may be that we could not detect an upregulation of Hsp70 under cold stress and that we therefore obtained baseline Hsp70 levels. More general, other proteins may also play a role in shaping the still poorly understood resistance to nonfreezing low temperatures, potentially obscuring any effect, if present,Nafcillin Sodium from Hsp70 alone. Instead of an upregulation of Hsp70 after the cold shock, we found a slight downregulation. In the copper butterfly Karl et al. did report an upregulation of Hsp70 after a 1 h cold stress followed by a 1 h recovery period. Yet, in line with our results, other studies found that levels of Hsp70, if anything, decreased during a cold period and only started increasing several hours after the cold shock ended. Activation of the heat shock factors is probably incomplete under a short period of cold stress, and longer recovery times would have shown an upregula- tion. Whatever the reason, this lack of upregulation during the experiment indicates that baseline Hsp levels may have contributed in shaping the latitudinal differences in recovery times in current experiment. Upregulation of Hsp70 after cold stress may be more important in reducing damage long after the chill coma has ended as shown in another insect and may not be that important in keeping chill coma recovery times short. Similarly, Kosˇta ́ l and Tollarova ́ – Borovanska ́ suggested that high Hsp levels during dormancy may represent an anticipatory protection against a variety of environmental insults. Hsp70 levels were lower in the two treatment groups with the highest growth rates, southern larvae and larvae reared at the high temperature, consistent with an energetic cost of rapid growth. Importantly, also at the individual level faster growing larvae had lower Hsp70 levels.