The mass-outbreak of leafhoppers that occurred over almost all of Japan in 1940 led to the institution of a national pest forecasting system in 1941. Since then the method of forecasting insects, especially rice stem borer, has been modified to meet every change in the rice cultivation.
　In case of the rice stem borer forecasting should be, at least, composed of two elements; namely forecasting the time of insect appearance and population assessment. In all events, however, it is most desirable to forecast the peak-date of moth appearance, because the opportune time to apply insecticides can be worked out by knowing this. To this end, a so called "experimental method of forecasting" has been established and adopted by the observatory station. This method is based upon the time that moth appearance can be seen by measuring the degree  of some physiological development in the larval stage.
　On the other hand, although the method to forecast the population is unsatisfactory, many efforts have been made recently and some method which is better seems to developing. In fact, the goodneess of fit forecasting has reached as high as 90% or more of late year.