Through the collecting investigation of mosquitoss by light trap in Okayama prefecture in 1960, usually observed phenomenon that the incidence of Japanese B encephalitis follows the maximum peak of Culex tritaeniorhynchus about 2 weeks or 1 month later was not clearly observed.
A suggestion that the outbreak of Japanese B encephalitis begins south and spreads to north was not observed.
A prodigiously great number of C. tritaeniorhynchus were caught on each collection at some restricted places at Kurashiki City, where they might hibernate in Winter.
