[Aim]  To determine the effect of exposure to commonly used insecticides on expression of P450 genes in the wasps Trichogramma japonicum and Trichogramma chilonis, in order to further understanding of the mechanisms responsible for insecticide tolerance in these species, and promote their use for pest management purposes. [Methods]  Expression of the P450 genes of T. japonicum and T. chilonis populations that were either resistant, ortolerant , to imidacloprid, thiothiazide, thiazone and nitenpyram was determined using RT-qPCR. [Results]  The expression of several P450 genes varied across populations of T. japonicum. Among these, CYP4C1 and CYP4G15 were significantly upregulated in thiothiazide-tolerant populations, CYP4C1, CYP6A2, and CYP9E2 in thiazone-resistant populations, and CYP4C1, CYP4G15, CYP6A14, and CYP6K1 in nitenpyram-resistant populations of T. japonicum. CYP4AA1, CYP6A2, CYP9AG4, CYP9E2, CYP9P3, CYP307A1, and CYP315A1 were upregulated in imidacloprid-tolerant populations of T. chilonis, CYP9AG3 in thiothiazide-tolerant populations of T. chilonis, and CYP4AA1, CYP6A2, CYP9E2, and CYP307A1 in nitenpyram-tolerant populations of T. chilonis. [Conclusion]  These results show that two Trichogramma species from resistant, or tolerant, populations differ in P450 gene expression, a finding that improves understanding of the mechanism underlying pesticide resistance in these species, and lays a solid theoretical foundation for the release of resistant, or tolerant, Trichogramma wasps for biological control.