BIOLOGICAL STUDIES OF XANTHOPIMPLA STEMMATOR (THUNBERG) (HYMENOPTERA,ICHNEUMONIDAE), A PARASITOID OF LEPIDOPTERAN STEM BORERS

The solitary pupal endoparasitoid, Xanthopimpla stemmator (Thunberg), was introduced into South Africa from Mauritius as a biological contro l 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 compri sing 64% of the progeny. There was a significant correlation between d ensity of parent population and sex ratio of offspring, the greater th e density the higher the percentage of female offspring. Minimum thres hold temperature for development was 11.44 degrees C and thermal const ant 248.2 day-degrees. Females lived longer than males and the presenc e of hosts shortened the life of both sexes. The stem borers Chile par tellus (Swinhoe) and Eldana saccharina Walker were suitable hosts for X. stemmator whereas the bollworm Helicoverpa armigera (Hubner) was no t. Xanthopimpla stemmator was released in maize and grain sorghum fiel ds 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.