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Objective. To evaluate the functional activity of entomopathogenic strains of Bacillus thuringiensis 87 and 800 during bioassay on the target object — the Colorado beetle population depending on the characteristics of bacterial cultivation. Methods. Microscopic, microbiological (to cultivate bacteria on different media and determine the spore titre), bioassay (on the larvae of the natural population of Leptinotarsa decemlineata Say during the period of dominance of the younger age (L1–2), model laboratory and field experiments with potatoes (to determine the degree of entomocidity of the studied strains), weight (to estimate the yield of potatoes during continuous harvesting from plots), biochemical (to determine the content of starch and sugar in potato tubers), statistical. The entomocidal activity of the spore-crystal complex of bacteria was calculated according to Abbott and Franz. Results. The highest productive yield of entomocidal components in liquid presentations of B. thuringiensis occurs on yeast-polysaccharide and cabbage digest media (spore titre ranges from 2.2 to 3.1 billion/mL and 3.6 and 4.7 billion/mL, respectively). According to the entomocidal activity against the larvae of Leptinotarsa decemlineata Say. (L1–4), strains of B. thuringiensis 800 and 87 demonstrated effective parameters from 96.0% and higher at Day 10 of the laboratory experiment. In field conditions, the high functionality of B. thuringiensis 87 (entomocidal activity 95.0–98.0 %), which is not inferior to the chemical variant of spraying potato plants (Koginor, where the death of larvae at Day 7–10 is 96.0–99.0 %). Conclusion. As a result of the conducted research, the efficiency of the use of natural strains of B. thuringiensis 87 and 800 in the formation of potato plant protection systems against phytophages Leptinotarsa decemlineata Say was proven. This confirms high potential of justified application of these strains in agricultural production. |
