Ecdysis triggering hormone (ETH) is a neuropeptide known for its role in the orchestration of ecdysis. However, its role in the regulation of Juvenile Hormone (JH) synthesis is unknown. In Aedes aegypti, JH is synthesized by the corpora allata (CA) and titers are tightly regulated by allatoregulatory factors. In this study I describe the effect of ETH on JH synthesis during the late pupal stage and in the adult female after blood feeding. Analysis of ETH receptor (ETHRs) expression showed that ETHRs are present in both the CA and the corpora cardiaca (CC), a neurohemal organ. The data suggest that ETH regulates JH synthesis directly through its receptors in CA. Our results show that in pupa, ETH has a stimulatory effect on JH synthesis while in adult blood fed females, ETH is inhibitory. These findings constitute the first evidence of ETH as a regulatory peptide in mosquito JH synthesis.