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Insecticidal activity of Bacillus thuringiensis crystals and thymol mixtures

Konecka, Edyta, Czarniewska, Elżbieta, Kaznowski, Adam, Grochowska, Joanna
Industrial crops and products 2018 v.117 pp. 272-277
Bacillus thuringiensis, Cydia pomonella, Dendrolimus pini, Spodoptera exigua, additive effect, bacterial toxins, biological production, chemical constituents of plants, crystals, hemocytes, insect larvae, insect pests, insecticidal properties, mixing, synergism, thymol, viability
Our research provides a proposition of biopreparation that combines insecticidal factors acting in synergy against plant-feeding pests of order Lepidoptera. We propose the usage of mixtures of B. thuringiensis crystals and thymol against insect pests. We determined, for the first time, the character of interactions between the components of this biopreparation against three different lepidopteran pests’ species representing different families: Cydia pomonella L., Spodoptera exigua Hübner, and Dendrolimus pini L. from families Tortricidae, Noctuidae, and Lasiocampidae, respectively. Mixing the B. thuringiensis crystals and thymol in proportion 1:100 exerted synergistic interaction against C. pomonella, D. pini and S. exigua. Combining the crystals and thymol in proportion 1:250 resulted in synergistic interaction against D. pini and S. exigua. An increase of thymol concentration to 500 ng per 1 ng of crystals demonstrated the additive effect of thymol and crystals in this combination against D. pini and S. exigua. The same effect was observed against C. pomonella and S. exigua when appling 1000 ng of thymol with 1 ng of crystals. The addition also occured between 1500 ng thymol mixed with 1 ng of crystals against C. pomonella. However, applying the combination of crystals and thymol in proportion 1:15 000 against C. pomonella showed antagonistic interaction between phytochemical and bacterial toxins. We did not find any differences in morphology and viability of haemocytes that had been isolated from caterpillars fed with thymol, crystals and the mixture of these components in comparison with the control insects. Our results suggest that the use of mixture composed of B. thuringiensis crystals and thymol in which the concentration of crystals is ≥0.4% increases the insecticidal efficacy of the formulation and, therefore, it allows for application of lower doses of the mixture to control the lepidopteran pests.