Insecticidal effects of substances from cinnamon bark – eugenol, trans-cinnamaldehyde and cinnamaldehyde on Tenebrio molitor (Coleoptera: Tenebrionidae)

Abstract

The use of synthetic pesticides is increasingly limited due to their environmental impact, development of pest resistance, and confirmed negative effects on human health. At the same time, the demand for food grown in accordance with the principles of organic farming is increasing. Integrated Pest Management (IPM) promotes the use of biopesticides - natural substances with low toxicity to nontarget species as alternatives to synthetic pesticides. These substances include, among others, compounds found in the bark of the Ceylon cinnamon tree (Cinnamomum verum J. Presl, Lauraceae), such as eugenol, trans-cinnamaldehyde and cinnamaldehyde. However, the mechanism of their action has not been sufficiently researched. Therefore, this study compared the effects of these substances and various modes of their application on important pests of cereal crops and food stores and on a model organism, Tenebrio molitor beetle (Coleoptera: Tenebrionidae). The tested compounds were administered by injection, inhalation, food, by immersing the tested larvae or by contacting them with substratum soaked in the tested compound. The results allowed us to determine the LT₅₀ parameter, and the probit analysis estimated the LC_20/30/50/95 values. The results showed that the most effective route for administering cinnamon bark compounds is contact and injection, and the most effective compound is eugenol, with an LC₅₀ value of 2.01 μl/ml (contact). The lowest LC₅₀ values for trans-cinnamaldehyde and cinnamaldehyde were 6.28 μl/ml (injection) and 15.66 μl/ml (contact), respectively. Second, cinnamaldehyde and trans-cinnamaldehyde (filter paper tests at 200 μl/ml) and eugenol (immersion test at 300 μl/ml) had the lowest LT₅₀ values. The test results also indicate that all the tested compounds cause morphological malformations in T. molitor larvae in the concentration range of 50–300 μl/ml. This research highlights the insecticidal potential of eugenol and cinnamaldehydes, indicating that cinnamon bark-derived pesticides could effectively control T. molitor populations. These compounds are promising for developing eco-friendly biopesticides.