Ten strains of Bacillus thuringiensis (Bt) were isolated from sludges collected from wastewater treatment plants and two strains were isolated from dead Tortricidae larvae sample collected from forest (Quebec, Canada). The bacterial isolates were characterized by PCR method using specific primers for amplification of the Cryl gene (Cry IA and Cry IC genes codes active toxin against Lepidoptera species), Cry III gene (active against some Coleoptera species) and Cry IV gene (toxic against Diptera species). This study showed that all the 12 bacterial strains yielded a PCR product for the Cry IA gene and five of them also possessed the Cry IC gene. The insecticidal activity or entomotoxicity of these strains against Lepidoptera species was confirmed through bioassays using third and fourth instar Choristoneura fumiferana larvae. Growth of new (INRS) strains in wastewater sludge gave higher values of viable total cell count and spore counts in comparison to standard strains. The entomotoxicity potential of the MS isolated strains varied between 10650 and 14750 SBU/mu l. These results of insecticidal activity were substantially higher than the reference strain of Bt var. kurstaki with an entornotoxicity value of 10789 SBU/mu l. Thus the isolated Bt strains could be used to develop a more efficient process for biopesticide production. (c) 2005 Elsevier Ltd. All rights reserved.