Abstract
In the preceding paper, the author reported that the decrease in number of femaleCulex tritaeniorhynchus trapped paralleled the decrease in human incidence. In an attempt to elucidate the factors affecting the decrease of mosquito, meteorological conditions and annual consumption of weeding agents and insecticides were analyzed. The following facts were noted.
In the years (1966,1967) when many mosquitoes were trapped, the mean temperature of the first decade of March (4.6-7.9°C) was higher than that of ordinary year (4.0°C). In 1969-1973, it was lower than the ordinary year and the number of mosquitoes was fewer than before.
Throughout the period, consumption of two insecticides, γ-BHC and Sumithion, was increased and negatively correlated with the mosquito population, while the consumption of other insecticides or weeding agents was the same or decreased. All these findings and the literature suggest that the mean temperature of the first decade of March and the consumption of two insecticides are the factors which influence the mosquito number.
