Relationship between cold hardiness and supercooling point in Aedes albopictus eggs.

For many insects, low temperatures are not lethal unless their tissues freeze. To determine whether freezing is the cause of low temperature mortality of Aedes albopictus eggs, we measured their lower lethal temperature, the temperature that causes 50% mortality in a population, and supercooling point, the temperature at which the tissues freeze. Tropical and temperate Ae. albopictus eggs were tested under different diapause and cold acclimation conditions. Temperate Ae. albopictus eggs had a lower lethal temperature than tropical Ae. albopictus eggs. Diapause and cold acclimation decreased the lower lethal temperatures of temperate eggs. However, neither diapause, cold acclimation, nor geographic origin affected Ae. albopictus egg supercooling points. All lower lethal temperatures were above -13 degrees C and all supercooling points were below -26 degrees C, indicating prefreeze mortality. Eggs of Aedes triseriatus and Aedes aegypti also died before they froze.