Essential Oil from <i>Curcuma Longa</i> Leaves: Using Nanotechnology to Make a Promising Eco-Friendly Bio-Based Pesticide from Medicinal Plant Waste

Nano-emulsions of essential oils (EO) and their chemical constituents are promising raw materials for the ecological control of <i>Tribolium castaneum</i>. <i>Curcuma longa</i> L. is a plant known for the properties of its rhizome, which is used in food, health, and hygiene products. Although its leaves are considered by-products with no commercial value, they produce an essential oil rich in bioactive monoterpenoids. This study aims to evaluate the repellency of nano-emulsions containing the EO from leaves of <i>C. longa</i> or its three main chemical constituents against <i>T. castaneum</i>. The representative mixture of EO extracted in four different months showed <i>p</i>-cymene (26.0%), 1,8-cineole (15.1%), and terpinolene (15.5%) as major compounds. Nano-emulsions of EO (HLB 16.7), terpinolene (HLB 15.0), 1,8-cineole (HLB15.0), and <i>p</i>-cymene (HLB 15.0) were repellent at concentrations of 11 μg/cm² (EO, terpinolene, and <i>p</i>-cymene) and 1.1 μg/cm² (1,8-cineole). The EO nano-emulsion droplet size increased linearly over time, remaining below 300 nm for 35 days. The EO nano-emulsion proved to be a green alternative to synthetic pesticides, as it was safe against the bioindicator <i>Chlorella vulgaris</i>. Furthermore, its main constituents were able to inhibit in silico the enzyme telomerase of <i>T. castaneum</i>, which is an enzyme essential for life. This study provides ideas for the utilization of EO from leaves of <i>C. longa</i> as raw material for new environmentally friendly plant-derived nanobiopesticides.