Temperate populations of _Aedes_ _albopictus_ overwinter as eggs in a photoperiodically-induced facultative diapause. Tropical populations are not photoperiodic and do not diapause. Eggs of temperate strains are more cold hardy than those of tropical strains. Cold acclimation and diapause enhance cold hardiness of only temperate strains. Cold hardiness induced in the laboratory is comparable to that induced in the field in northern Indiana.