Further Notes on the Early Summer Outbreak of the Oriental Armyworm on Grasslands of Tohoku District, 1971

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  • 東北地方の草地における1971年初夏のアワヨトウ異常発生原因特に成虫飛来日の再検討
  • トウホク チホウ ノ ソウチ ニ オケル 1971ネン ショカ ノ アワヨトウ

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In the early summer of 1971, an extensive outbreak of the oriental armyworm, Mythimna separata Walker, occurred on grasslands of Tohoku district, northern Japan. In a previous paper it was suggested that the outbreak might be caused by an immigration of the moth swarms brought by a southwesterly air-current which came from continental China to northern Japan on 25th May. However, the critical period of moth immigration is estimated to be in early June, if we take the thermal constant and the threshold temperature of the army-worm growth obtained by Okuyama and Tomioka as the substitute for those by Lin and Cheng, which were formerly employed for the estimation. During the early half of June, a strong southwesterly wind established over Tohoku district on the night of 4th June. Synoptic weather charts indicated that this wind followed a depression which rapidly moved towards northern Japan from Honan district of eastern China, where the moths emerge during late May and early June. On the other hand, the depression which caused the south-westerly wind of 25th May originated in the more south, where the moth activity was terminated ahead of this period. The results of moth trapping in two localities of Tohoku district supported the supposition that the moth swarms invaded the district on 4th June. Some comments upon the topographic effect on the migratory routes in mountainous areas of the district were given herewith.

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