Nano-emulsions of the essential oil of Baccharis reticularia and its constituents as eco-friendly repellents against Tribolium castaneum

Abstract

Nanoproducts based on natural products have been studied as ecologically and economically sustainable alternatives for crop pest control. Baccharis reticularia DC. is a shrub endemic to Brazil, which leaves are traditionally used in aromatic medicinal baths. This study aims to evaluate the repellent activities of nano-emulsions containing the B. reticularia phytochemically characterized essential oil and some of its monoterpene constituents (limonene, α-pinene, and β-pinene) against Tribolium castaneum (Herbst). Essential oil was obtained by hydrodistillation of fresh leaves and stems and yielded 0.28 % (w/w). The main constituents of the essential oil were: limonene (14.6 %), β-myrcene (12.6 %), and bicyclogermacrene (12.5 %). The required hydrophile-lipophile balance (rHLB) of the nano-emulsions were: 13 (α-pinene) and 15 (essential oil, limonene, and β-pinene). All nano-emulsions showed mean droplet sizes bellow 200 nm and remain stable, at least, for 28 days (limonene), 90 days (β-pinene), or 150 days (essential oil and α-pinene). All nano-emulsions exhibited repellent activity against T. castaneum at 8.8 μg/cm2. Limonene and α-pinene were the most active nano-emulsions, showing significant repellent action at 1.1 μg/cm2, which indicates that these compounds contribute to the repellent action of the essential oil of B. reticularia. The present study opens perspectives for the utilization of B. reticularia essential oil and its constituents as raw material of new promising nanopesticides produced using a low energy, solvent-free and ecofriendly method. Thus, this work contributes significantly to the search for new ecologically correct strategies for the control of T. castaneum.