Low Temperature Treatment Impacts Aedes (Stegomyia) aegypti Populations from Southern Brazil

The mosquito Aedes aegypti is the main Brazilian arbovirus transmitter. Temperature exerts a direct influence on its development. This study evaluated the survival of immature stages (egg, larva, pupa) of Ae. aegypti populations from Curitiba and Foz do Iguaçu, two municipalities in the Paraná State, a subtropical region in the south of Brazil. Two experiments were performed at 9°C (the winter median lower minimum temperature in Curitiba and Foz do Iguaçu): In the first, pools of embryonated eggs were incubated inside the water at 9°C, with a hatching stimulus, for periods ranging from 5 to 20 days. No hatching was observed for both populations. After these periods, eggs were transferred to optimal temperature (27°C) and hatching occurred for eggs incubated at 9°C between 5 and 14 days, with viability decreasing with increased incubation periods. No hatching occurred with 15-20 incubation periods, although eggs contained fully developed larvae. In the second experiment, L1 larvae and pupae were observed in water at 9°C. L1 developed to L2 in both populations but died after a 3- and 4-day period at 9°C for Curitiba and Foz do Iguaçu, respectively. Pupae remained alive for 15 and 13 days in Curitiba and Foz do Iguaçu, respectively, but did not become adults. These results confirm that 9°C temperature decreases viability relative to the exposure time and hampers adult formation, compromising the species' fitness. The South region is the coldest in Brazil and Curitiba and Foz do Iguaçu Ae. aegypti populations are not able to cope with its low temperatures.