In temperate regions, the seasonal dynamics of Aedes aegypti (L.) (Diptera: Culicidae) is mainly influenced by temperature. It is assumed that, during the winter season, the population remains as eggs and that the development and population growth of surviving eggs begin during the following spring. The aim of the current study was to assess egg hatching of Ae. aegypti during the winter in Buenos Aires city (Argentina), and analyze the survival of immature stages. The experiments consisted of immersing eggs and studying the development of immature stages of cohorts from June and September under natural temperature conditions. The proportion of hatched eggs was compared between weeks of immersion and related to environmental variables. Survival was compared among cohorts and the development rate was related to the mean temperature during development. The results showed that, with few exceptions, egg hatching was over 45% during the winter period. The proportion of hatched eggs was positively associated with immersion temperature, pre-immersion temperature and photoperiod. The immature stages completed the development during the cold season, with a trend toward increased survival of late-hatching cohorts. Survival was 30% at 13.2 °C and above 90% at 20 °C, whereas the development time at low temperatures was 49.4 d at 13.2 °C and 17.7 d at 20 °C. The high hatching and survival compared with other studies suggest that the local population might be adapting to winter conditions. The anticipated emergence of adults would be adaptive if they are able to reproduce successfully in the early spring.

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Aedes aegypti larvae that develop in containers largely depend on plant detritus as a source of nutritional resources. However, few studies have evaluated the performance of immature individuals under natural amounts and quality of this food source. Here, we aimed to assess the effect of the variation in the accumulation time and amount of detritus on life history traits of Ae. aegypti under semi-field conditions. Ae. aegypti larvae were raised with detritus collected in different sites to represent natural variability in its amount, simulating short (28 days) and long (70 days) accumulation. A control with optimal food conditions (yeast) was included. Survival, development time and wing length of adults were compared among treatments. Survival was relatively high in all treatments. Development time was similar among treatments but significantly longer and more variable in containers with the lowest detritus amounts. Wing lengths were smaller in the treatments with detritus than in the control, especially in females. The results support the hypothesis that, in a temperate region, Ae. aegypti larvae may have a nutritional limitation, at least in some containers, and emphasize the importance of performing experiments that simulate the environmental conditions to which individuals are exposed in nature.

In many insects, short photoperiods induce females to lay diapausing eggs, which are associated with a reduction in female fecundity, and/or with an increase in their growth rate, allowing for a larger size at adulthood. The effects of short photoperiods may also differ among populations, depending on the different selection pressures imposed by the winter conditions. Thus, this study aimed to experimentally assess the effects of short photoperiods on Aedes aegypti, an invasive mosquito species that also vectors several viral diseases. We compared life history parameters of the females reared from the first larval instar under contrasting photoperiods, in two populations from the temperate region of Argentina, one with a milder winter (BA) and the other with a harsher winter (SB). The results showed a significant increase in the time to oviposition, a trend to a larger size of females (significant only for SB) and higher inhibition of egg hatching (more pronounced in SB), in response to short photoperiods. No differences in fecundity were detected among treatments. The different reaction norms of the populations in female body size and egg hatching response suggest an adaptation to local conditions, which might favour a further expansion of A. aegypti towards colder climates.