Adaptation to temperate climates: Evidence of photoperiod-induced embryonic dormancy in Aedes aegypti in South America

Dormancy is a developmental arrest in arthropods, in response to unfavorable conditions in temporally varying environments. In Aedes aegypti, the supposed inability of eggs to inhibit hatching has been used to explain the restriction of this species to tropical and subtropical regions. However, the geographic range of Ae. aegypti is constantly expanding towards temperate regions. Thus, the aim of the present study was to assess the ability of Ae. aegypti individuals from a temperate region (Buenos Aires City, Argentina) to enter photoperiod induced dormancy. To this end, we exposed both the parental generation and the eggs to short-day (SD: 10L:14D) and long-day (LD: 14L:10D) photoperiods, and studied the temporal variation in egg hatching. The experiment consisted of 28 treatment combinations of three factors: parental photoperiod (SD or LD), egg storage photoperiod (SD or LD), and age of eggs (14, 28, 42, 56, 70, 91, and 112 days). The results showed a lower hatching response with the SD parental photoperiod, and a trend to higher hatching with longer egg storage time in all photoperiod treatment combinations. The egg storage photoperiod showed no effect on egg hatching. In both parental photoperiod treatments, egg replicates of most ages from different females showed a large variability, with some replicates with lowest hatching response and others with highest hatching response. Our results show the ability of Ae. aegypti to inhibit egg hatching in response to a short-day photoperiod, which could allow the further expansion of this species to regions with colder winters.