Previous theoretical studies and some empirical studies suggested that the factors which affect female availability should influence male reproductive behavior. We noticed the female post-emergence behavior as one such factor, and investigated how it might influence male reproductive strategy in the butterfly, Pieris rapae crucivora. In the field and the laboratory newly-emerged females stayed on the underside of leaves 2.5 hr after emergence before they flew voluntarily into the open where they are more visible to males. Time spent before initial flight correlated negatively with ambient temperature, and initial flights increased significantly the possibility that the female would be detected by males. To evaluate whether these results could explain the time schedule of males' search for females in the field, female availability was estimated by shifting the observed schedule of female emergence according to the relationship between initial flight and effective cumulative temperature. The resultant female availability correlated well with temporal changes observed in the number of mate-seeking males. Thermal conditions may influence male reproductive behavior via female post-emergence behavior, as well as via male body temperature.