Thymol-Based\nNatural Deep Eutectic Solvents: New Trends\nin the Development of Bioinsecticides

The growing concern about the harmful effects of insecticides\non\nhuman health and the environment has led to an expansion of the search\nfor sustainable substitutes. In this context, the topical bioactivity\nof different hydrophobic natural deep eutectic solvents (NADES) prepared\nfrom plant secondary metabolites was evaluated for the first time\nas bioinsecticides against Tribolium castaneum and Sitophilus oryzae. The studied\nNADES included thymol/eucalyptol (T/E), thymol/benzyl alcohol (T/B),\nand thymol/menthol (T/M), evaluated in a range from pure NADES to\na 1:3 molar dilution with acetone. Additionally, the toxicities of\nthe individual compounds and their acetonic noneutectic mixtures were\nassessed. In a preliminary assay, T/M showed the most acute toxicity.\nIn contact assays, T/M achieved 85% mortality for T.\ncastaneum and 100% for S. oryzae. In repellent tests, T/M had activity against S.\noryzae for 16 days but showed no repellency against T. castaneum. In order to confirm the existence of\neutectic mixtures in the dilutions employed in biological tests and\nto understand the spatial interactions between their components, all\nthe NADES were analyzed by NMR spectroscopy. The obtained results\nallow us to conclude that the evaluated NADES, especially T/M, can\nbe considered as new alternatives for the development of bioinsecticides.