Forecasting adult emergence and abundance of spotted cutworm, Xestia c-nigrum in the Tokachi district of Hokkaido [Japan]

The seasonal and annual prevalence of adult spotted cutworms in the Tokachi district of Hokkaido was investigated with a light trap from 1973 to 1986. The average date for 50% capture was June 28 for the overwintering generation and September 3 for the first generation. The average number of adults captured the 757 for the overwintering generation and 5, 900 for the first generation with two distinct seasonal peaks for the separate generations. The hypothetical zero point and effective heat accumulation were obtained by minimizing the coefficient of annual variation in the heat accumulation until the date of 50% moth capture by the light trap. This afforded better prediction of the dates for both the overwintering and first generations than for experimentally-reared ones. There was high correlation between the number of captured overwintering-generation adults and the total precipitation in October and December of the previous year. The relationship is expressed by the multiple regression equation, Y=2.475-0.804X7+1.175X9 (R2=0.838), where Y, X7, and X9 represent the trapped adult number and precipitation in October and December as logarithmic values, respectively. This equation estimates the real adult number with good accuracy. However, in the first generation, the correlation between the adult number and meteorological factors was not so high.