Three criteria necessary for larval overwintering of Spodoptera litura were determined from the results of laboratory and field experiments in order to predict the overwintering areas of this insect in Japan. the first criterion is for the daily minimum temperature in winter to be higher than -5°C, which is the lethal low temperature of the larvae. On the other hand, larvae are known to require a daily effective temperature for development (DET) of more than 0.9 degree-days (DD). this necessary DET is decided in accordance with cold intensity and duration of sub-zero temperatures per day. Surplus or deficient DET for long term survival of larvae per day was calculated by subtracting the necessary DET from the actual DET. Consequently, the second criterion is summarized as follows: cumulative surplus DETs≧cumulative deficient DETs in winter (Dec. 15th to Mar. 15th). The third criterion is for the number of consecutive days with deficient DET to be 30 or less. these three criteria must be met in order for overwintering of S. litura larvae to occur. the likely overwintering areas of S. litura in Japan were predicted by analyzing temperature data of the Automated Meteorological Data Acquisition System (AMcDAS) on the basis of the three criteria mentioned above.