Abstract
This paper is a preliminary report on the adult biology and the role of bird predation on the adult stage of the fall webworm, Hyphantria cunea, accidentally introduced in Japan. The results are summarized as follows : (1) Progress of eclosion of the overwintering generation was restrained by low temperature, and the seasonal fluctuation of eclosion was precisely detected by the ligth-traps as well as by the direct observation. (2) The eclosion occurred during the evening and the night, and mating at dawn. Sexual flight of males ceased just after the beginning of the dawn chorus of the tree sparrow. (3) Fresh adults were very conspicous when resting on tree-trunks and they were intensively picked up by tree sparrows and grey starlings. From the preliminary numerical observations, tree sparrows were considered to be playing an important role in controlling the number of H. cunea.