Diapause and Related Phenomena in Culex Mosquitoes: Their Relation to Arbovirus Disease Ecology

Abstract

Most mosquitoes in the genus Culex appear to overwinter as inseminated female adults, although individuals that have actually been observed overwintering in nature represent only a few species. Moreover, searches for such relatively common species as Culex salinarius Coquillett and C. restuans Theobald have repeatedly been unsuccessful. Aside from the importance of mosquito diapause as a biological phenomenon, there has been considerable interest in the subject because of the possibility that overwintering female mosquitoes may serve as hibernal reservoirs of arboviruses causing human and animal diseases (33, 81). Two North American mosquito-borne arboviruses of public health importance are transmitted by species of the genus Culex: St. Louis encephalitis (SLE) by C. pipiens Linneaus and C. tarsalis Coquillett, and western equine encephalomyelitis (WEE) transmitted by C. tarsalis. In Asia, C. tritaeniorhynchus Giles is the vector of Japanese encephalitis (JE) in temperate regions. Until the convincing demonstration of transovarial transmission of an arbovirus by a species of mosquito (115), few biomedical scientists gave much credence to the idea that mosquitoes played an important role as winter reservoirs of arboviruses. The isolation of SLE virus from overwintering Culex pipiens (3) focused attention on Culex mosquitoes in this context, although these isolations were not novel.