Progress in studies on the overwintering of the mosquito Culex tritaeniorhynchus

A detailed review is presented of half a century's research in Japan, Korea and the temperate zone of China on the overwintering of Culex tritaeniorhynchus, the main vector of Japanese encephalitis. The evidence indicates that in the temperate zone, two types of overwintering strategy can be distinguished in Cx. tritaeniorhynchus, ie survival by adults in situ in a dormant state, or migration by individuals which are in reproductive diapause. The authors contend that the former strategy is not very effective, and individuals which overwinter in this way do not constitute the main source of the next season's mosquito populations. On the contrary, new mosquito populations seem to be established by groups of adults which appear suddenly, early in the year, and which are probably windborne migrants from the south. It is concluded that further research into the mode of overwintering of Cx. tritaeniorhynchus should focus on the effective source of the populations which appear in temperate areas in early spring, and that efforts should be made to increase our understanding of the migration patterns of this species.