Sexual receptivity and mating behavior of the cabbage aphid parasitoid Diaeretiella rapae McIntosh were studied under laboratory conditions. When male and female D. rapae were paired females, males actively courted females, while females kept themselves away from males and displayed grooming behavior. Males became sexually active immediately after emergence and made mating attempts, whereas females took longer to become receptive to mating. Virgin males quickly detected female presence, resulting in a significant increase in the frequency of male courtship. Males encountered females within 5 min of pairing, and 90% of the males displayed courtship behavior by fanning their wings and chasing the female for mating. Before successful mating, males tended to approach females more often than females approached males. The time between pairing and mating in newly emerged females was longer than in 1-d-old females. The overall mating success in D. rapae was about 70%, and successful mating was largely dependent on females' decision to mate. Unlike females, males remained sexually receptive after mating.