none Entered (Aim) Superparasitism often occurs in parasitoids. In this study, we aimed to investigate the effects of superparasitism on the offspring growth and development of Cotesia ruficrus and to determine the factors that contribute to superparasitism. (Methods) The effects of oviposition times of C. ruficrus on the survival rate of the host (the 3rd instar larvae of Cnaphalocrocis medinalis) and the growth and development of the parasitoid offsprings, and the effects of exposure time and parasitoid density on superparasitism were detected in this study. (Results) Laboratory experiments demonstrated that the superparasitism occurred in C. ruficrus when it parasitized C. medinalis larvae. Female wasps, irrespective of the experience of oviposition, attacked hosts that had been parasitized by themselves or other individuals. The number of parasitoid cocoons increased with oviposition times, while the number of the dead parasitoid larvae increased when the host was parasitized 3 to 5 times. The mortality of the host before emergence of parasitoid adults increased with the oviposition times, and reached to 50% when the host was parasitized 5 times. Superparasitism prolonged the developmental duration, lowered the emergence rate and the female/male ratio of the parasitoid offsprings. The female body size of the parasitoid offsprings significantly decreased as the oviposition times increased, and the superparasitism rate increased with the parasitoid density and exposure time. (Conclusion) Ovipositing twice on host larvae shows to be the most beneficial to the growth and development of C. ruficrus offsprings, and ovipositing thrice causes superparasitism. Although superparasitism increases the number of parasitoid offsprings, it is detrimental to the progeny development. The superparasitism, therefore, should be avoided in mass rearing of C. ruficrus in laboratory, by means of controlling exposure time and density of the parasitoids. Oct 20 2014