This study is devoted to studying Bacillus thuringiensis antigens and their insecticide activity as critical feature in bacterial differentiation. 190 samples were examined for flagellar antigenicity as well as the insecticidal activity exhibited. From a serological perspective, 122 isolates (64.2%) were attributed to 8 H-serogroups, including 3 non-typeable and 65 unverified. The dominant serotype was H3abc (82% frequency); H6 was less frequent (8.5%). The other 6 serotypes accounted for a low frequency of occurrence (up to 1.5%). Of the 190 isolates tested, 125 (65.8%) formed bipyramidal and 63 (33.2%) represented spherical inclusions. All H3abc isolates contained bipyramidal inclusions. The same applied to H8ab and H7 isolates. Insecticide activity was noted in 70.1% of populations. 128 samples were toxic to both species (Bombyx mori, Aedes sp.). Another 3 samples were toxic only to B. mori, and 2 for Aedes sp. Of the samples that showed toxicity for both species, 97.6% belonged to bipyramidal paraspore inclusions (H3abc). All H7 samples were toxic to two insect species. Monotoxic B. thuringiensis against Aedes sp. were found only among organisms producing spherical parasporal inclusions in the cell. Examples of such microorganisms include an isolate of H4ab/43 serotype.