In many insects, female receives a large amount of sperm and ejaculates upon copulation, and keeps them in her uterus for some time, during which she stores sperm. After varying delays, the female removes unused sperm and ejaculates through sperm ejection behavior, which is known as a major mechanism for the post-copulatory sexual selection. In the fruitfly Drosophila melanogaster, timing of sperm ejection behavior is controlled by the diuretic hormone 44 (Dh44) pathway. To identify pathways that regulate Dh44 activities and sperm ejection, here we examine effects of olfactory cues. We will present our recent results suggesting that male odors can be one of upstream signaling pathway that modulates a brain neuropeptide pathway.