The aboveground activities of the larger black chafer (Holotrichia morosa Waterhouse) and the Korean black chafer (H. diomphalia Bates) adults were investigated in the field and laboratory from 1991 through 1992. In a field cage, H. morosa adults emerged from the ground between 7 : 40-9 : 00 p.m. and H. diomphalia adults emerged between 7 : 30-10 : 00 p.m. After emergence, both females and males flied actively for less than one minute in H. morosa, while males flied inactively and females did not fly at all in H. diomphalia. Once emerged, adults of the two species mated or fed on plant leaves and seemed to stay aboveground till dawn. H. mOTOsa adults were attracted to a blacklight trap mainly between 8 : 10-10 : 00 p.m. in the field. H. morosa males and females emerged from soil every other day in a glass cistern.