We attempted to search novelBacillus thuringiensisstrains that produce crystals with potential utility in plant protection and with higher activity than strains already used in biopesticide production. SevenB. thuringiensissoil and water isolates were used in the research. We predicted the toxicity of their crystals bycrygene identification employing PCR method. The isolate MPU B63 with interesting, according to us, genes content was used in evaluating its crystal toxicity againstCydia pomonellacaterpillars. The strain MPU B63 was cultured from water sample and hadcry1Ab,cry1B, andcry15genes. The LC50crystals of MPU B63 were compared to LC50of commercial bioinsecticide Foray determined againstC. pomonella(codling moth). The activity of MPU B63 inclusions against codling moth larvae was approximately 24-fold higher than that of Foray. The results are a promising introduction for further study evaluating the potential usefulness of isolate MPU B63 crystals in plant protection.

The purpose of this study was to evaluate potential usefulness of Bacillus thuringiensis crystalline toxin mixtures against crop pest representing the insect order Lepidoptera. Crystals of two B. thuringiensis strains, MPU B9 and MPU B63, were isolated using a gradient of sucrose density. Mixtures of crystals MPU B9/MPU B63 were prepared and their toxicity against the codling moth Cydia pomonella (Lepidoptera) was estimated. In parallel, the toxicity of separate crystal suspension of MPU B9 and MPU B63 was determined. The activities of the mixtures were compared with the toxicities of commercial biopesticides based on B. thuringiensis, recommended against lepidopteran pests. The LC 50 of crystal mixtures against the insects were lower than the LC 50 of suspensions of crystals of separate bacterial strains. Crystalline proteins of two B. thuringiensis isolates are synergistic in toxicity to C. pomonella. The activities of mixtures were higher in comparison with the toxicities of commercial bioinsecticide, which indicates a potential usefulness of mixtures in crop protection. This research participates in a search of a new virulent factor enriching a set of B. thuringiensis toxins already applied in the bioinsecticide production.

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