Experiments were carried out to detect and estimate the insect-killing effect of rapanone on the flour beetle T.castaneum. Two kinds ofessays were made: by ingestion and by contacto It was proved that rapanone has insecticide activity on T. castaneum. Relatively high LD50 were determined, in comprarison with those of conventional commercial insecticides. An inverse proportionality, between doses of rapanone and the mean productivity, was also found; adose of 7000 mg rapanone per kg standard culture medium is enough to exterminate, almost completely, a population of T. castaneum in one generation.