Winter dormancy in mosquitoes can be classified as diapause or quiescence. The primary function of diapause is seasonal adaptation, but it also serves to synchronize life cycles and determine patterns of voltinism. Among mosquito species that enter diapause, arrest of growth or development has been documented in each life history stage except the pupa. Only the female imago is known to undergo diapause. The potential relationships between overwintering mechanisms of certain arboviruses and their mosquito vectors and the demonstration of transovarial transmission by mosquitoes of several arboviruses provide ample justification for examining the phenomenon of diapause in overwintering mosquitoes in detail. In addition, the intrinsic biological significance of diapause as an adaptation for winter survival is well illustrated by the family Culicidae. Reproductive diapause is characteristic of insects preparing for migration or hibernation, and some species may undertake migratory flights prior to entering hibernation.