Differential survival of Aedes aegypti and Aedes albopictus (Diptera: Culicidae) larvae exposed to low temperatures in Taiwan.

Aedes aegypti (L.) and Aedes albopictus (Skuse) differ in their distribution in Taiwan. The former species is distributed in the south of Taiwan, whereas the latter is found throughout the island. One possible explanation proposes that low temperatures in the winter prevent the expansion of Ae. aegypti. Hence, the impact of low temperatures on immatures of both species was studied in the laboratory and in the field. Our study showed that, under most conditions, Ae. aegypti were more sensitive to low temperatures than Ae. albopictus both in the laboratory and in the field. The survival rates at 10 degrees C for the first and fourth instars of Ae. albopictus were significantly better than those of Ae. aegypti. At 2.5 and 5.0 degrees C, the first instars of Ae. albopictus survived better than the same stadium of Ae. aegypti, but the fourth instars of Ae. aegypti survived better. Short exposures to low temperatures did not affect the acclimatization of Ae. aegypti immatures but longer exposures did increase the physiological adaptation to low temperatures. For Ae. albopictus, exposure to low temperatures increases the acclimatization of this species. In field experiments, Ae. aegypti larvae had a significantly higher mortality than Ae. albopictus during exposures to cold fronts in the 2004 winter. We conclude that low temperatures in northern and central Taiwan have a negative impact on the distribution of Ae. aegypti, but this factor alone is not sufficient to prevent this species from occupying the rest of Taiwan.