chikungunya and Zika are arboviruses transmitted by the mosquito Aedes aegypti. Mosquito fecundity and egg viability are important parameters of vectorial capacity. Here we aim to understand, comparatively, the effects of Chikungunya virus (CHIKV) and Zika virus (ZIKV) infections on the fecundity and fertility of young and old Aedes aegypti females. Using artificial infection blood feeding experiments we observed that both cHiKV and ZiKV do not alter the number of eggs laid when compared to uninfected females, although the egg fertility significantly decreases in both young and old CHIKV-infected females. There is an upward trend of null females (infertile females) from 2.1% in young to 6.8% in old ZIKV-infected females. Together, our data revealed that CHIKV and ZIKV affects differently Ae. aegypti physiology, that may be related to different viral spread in nature. Chikungunya virus (CHIKV), a member of the Togaviridae family, Alphavirus genus, was first isolated in 1952 in Tanzania 1. Emerging and reemerging outbreaks have occurred since its discovery in several regions in Africa, Asia, Indian Ocean islands and Mediterranean areas in Europe 2,3. In Brazil, the first Chikungunya autochthonous cases occurred in 2014 4. The virus spread throughout the country 5 , being in co-circulation with dengue (DENV) and Zika (ZIKV) viruses during this period 6. Zika, a virus belongs to Flaviviridae family, Flavivirus genus, was first isolated in 1947 7. For 60 years, only sporadic Zika cases were reported in humans, however in 2007 an outbreak occurred in Yap Island, Micronesia 8. Subsequently, ZIKV expanded throughout the Pacific islands and reached the Americas in 2015, turning into an epidemic in Brazil. It is currently considered a new public health threat 9-11. Both arboviruses (Zika and Chikungunya) are transmitted by the bite of mosquitoes of genus Aedes 7,12,13. Among them, the Aedes aegypti is the main vector in the urban transmission cycle 14-16. This domestic and anthropophilic species is anautogenous (the females need blood supply for eggs maturation) 17. After one or more blood feedings, egg maturation occurs in about 3 or 4 days. Each period between blood feeding and egg laying is called gonotrophic cycle (GC) 17-19. An Ae. aegypti female is able to lay approximately 100 eggs per GC 20. The ingestion of more than one blood meal by mosquito females within a single gonotrophic cycle is called gonotrophic discordance and can occur in Aedes aegypti mosquitoes. This feature is involved in vectorial capacity and is very important for the transmission of viruses 21-23. Comparatively, the biology of the egg phase is less explored than other in the mosquito life cycle. The Ae. aegypti eggs can survive for long periods in dry conditions at the end of their embryonic development 17,19,24-26. This important feature is related to ecological issues such as dormancy, that enables the embryo to survive