COMBINING RELEASE ESTABLISHMENT OF DIADEGMA-SEMICLAUSUM (HELLEN) (HYM, ICHNEUMONIDAE) AND BACILLUS-THURINGIENSIS BERL FOR CONTROL OF PLUTELLA-XYLOSTELLA (L) (LEP, YPONOMEUTIDAE) AND OTHER LEPIDOPTERAN PESTS INTHE CORDILLERA REGION OF LUZON (PHILIPPINES)/

In 1991, the Philippine-German Biological Plant Protection Project (PG BPPP) started to release D. semiclausum I, a larval parasitoid of P. x ylostella, at a large scale in the two highland provinces Benguet and Mountain Province, Northern Luzon, Philippines. The intention was to c ontrol 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 ad ult beneficials were released at a ratio of 1 male: 2 female adults in farmer's fields. By the summer 1992 the parasitoid, released at four different areas, proved to be established in 11 out of 24 municipaliti es of the two provinces and was spreading to other areas. In combining D. semiclausum and B. thuringiensis (Bt), a strategy for the biologic al control of P. xylostella was developed. Two control threshold level s for the application of Bt, one for P. xylostella-larvae at four larv ae/plant and one for all the other lepidopterous larvae feeding on cru cifers at 0.5 larvae/plant were assessed in several field trials after the establishment of D. semiclausum. Either population exceeding thes e levels initiated the application of biological insecticides based on Bt. Results of field trials indicated a possible reduction of insecti cide application by at least 50-70%.