In 1991, the Philippine-German Biological Plant Protection Project (PGBPPP) started to release D. semiclausum, a larval parasitoid of P. xylostella, at a large scale in the two highland provinces Benguet and Mountain Province, Northern Luzon, Philippines. The intention was to control this serious pest in cruciferous crops by biological means. The parasitoid was imported from Indonesia and successfully mass-reared. The hatching rate of D. semiclausum was around 90% and the sex ratio (male: female) 1:0.8. From April 1991 to June 1992 more than 12 000 adult beneficials developed. Two control threshold levels for the application of Bt, one for P. xylostella-larvae at four larvae/plant and areas. In combining D. semiclausum and B. thuringiensis (Bt), a strategy for the biological control of P. xylostella was one for all the other lepidopterous larvae feeding on crucifers at 0.5 larvae/plant were assessed in several field trials after the establishment of D. semiclausum. Either population exceeding these levels initiated the application of biological insecticides based on Bt. Results of field trials indicated a possible reduction of insecticide application by at least 50-70%. none