The solitary pupal endoparasitoid, Xanthopimpla stemmator (Thunberg), was introduced into South Africa from Mauritius as a biological control agent of lepidopteran stem borers of grain crops and sugarcane. The biology of the parasitoid was studied in the laboratory The mean pre-oviposition period of females was five days and oviposition period 64 days. Each female produced a mean of 95 offspring, with females comprising 64% of the progeny. There was a significant correlation between density of parent population and sex ratio of offspring, the greater the density the higher the percentage of female offspring. Minimum threshold temperature for development was 11.44 degree C and thermal constant 248.2 day-degrees. Females lived longer than males and the presence of hosts shortened the Life of both sexes. The stem borers Chilo partellus (Swinhoe) and Eldana saccharina Walker were suitable hosts for X. stemmator whereas the bollworm Helicoverpa armigera (Hubner) was not. Xanthopimpla stemmator was released in maize and grain sorghum fields in the Transvaal during four growing-seasons between 1987 and 1993. A few recoveries of parasitoids were made from the release sites, but X. stemmator failed to establish itself. The potential of X. stemmator as a biocontrol agent of lepidopteran stem borers in South Africa is discussed.