Sudden occurrence of the common cutworm, Spodoptera litura (Lepidoptera:Noctuidae) in southern Japan during the typhoon season

Daily records of Spodoptera litura males caught in pheromone traps at Saga and Kagoshima (150 km south of Saga on the Kyushu mainland) were compared during 1990 and 1995, in relation to meteorological conditions. The temporal patterns of occurrence were similar at the two locations, but the total number of males caught at Kagoshima was two or three times larger than that at Saga. Prominent peaks in catches during the rainy seasons in early summer and early autumn were also characteristic of the Kagoshima but not the Saga records. There were essentially no correlations between the numbers of males caught in any years and the catches of the preceding autumn. The most conspicuous feature of these records was the sudden increases in many cases in the male catch recorded at the time of the approach of typhoons in these areas, after mid-August. Our estimations of developmental rates based on the effective accumulative temperature of this species generally failed to indicate local emergence of moths corresponding to peaks in trap catches at about a one generation interval preceding a typhoon's approach. These typhoons generally passed the Southwest Islands of Japan and ran through the East China Sea before approaching Kyushu. Thereafter, the male catch tended to increase prominently in autumn. The possibility of overseas long-distance migration of this non-diapausing species when typhoons approach Kyushu is discussed.