Adaptations of the nucleolar organizer regions (NOR) banding technique using precipitation of silver salts significantly improved the NOR characterization of some species of hymenopterans and one coleopteran. The bee Melipona marginata (2n = 18) showed one metacentric pair of chromosomes with a NOR in the pericentromeric position. The parasitic wasp Mellitobia australica (2n = 12) also showed one metacentric pair with a strongly Ag-positive NOR. The male lady-beetle Cycloneda sanguinea (2n = 18 + Xy(p)) displayed a NOR on a pair of acrocentric autosomes. In the male Euglossa sp. (a haplodiploid species) (n = 21) the NOR were multiple, and occurred in five chromosomes. In the bee Plebeia sp. 1 (2n = 34) the NOR seemed restricted to one of the homologues of a metacentric pair. The systematic advances brought out by using this technique in the context of current theories of karyotypic evolution of these taxa are described and discussed.