SELECTION OF SPECIES AND NUMBER OF RELEASES OF Trichogramma FOR SUPPRESSION OF MAJOR PEST OF CABBAGE, TOMATO AND MAIZE

Trichogramma is an important egg parasitoid on lepidopterans and per cent parasitizing efficiency, egg desiccation, egg hatching, parasitoid emergence and per cent female ratio of seven Trichogramma species was studied against Plutella xylostella on cabbage, Helicoverpa armigera on tomato and Chilo partellus on maize in order to select appropriate Trichogramma species for each pest for determination of the dosage and frequency of release for effective suppression of above mentioned pests. The dosage and frequency of release were determined based on cost : benefit ratio (CBR). T. pretiosum (arrehenotokous) was selected for P. xylostella and H. armigera as it provided higher parasitism, i.e., 45.3 and 49.3 per cent, whereas T. chilonis gave an higher parasitism of 43.9 per cent against C. partellus. For suppression of P. xylostella and H. armigera, arrehenotokous form of T. pretiosum should be released @ 50,000/ha twice during the brood of the pest at weekly interval and for suppression of C. partellus, T. chilonis should be released @ 50,000 twice during the brood of pest at weekly interval. The CBR was higher 1:2.1 and 1:7.6 when T. pretiosum was released twice at @ 50,000/ha to control P. xylostella and H. armigera, respectively, whereas it was 1:3.5 when T. chilonis was released at @ 50,000/ha to control C. partellus, compared to 1 or 3 releases and also when released at higher rate, i.e., @ 100,000/ha, 1-3 times.