Optimizing the performance of Piper mikanianum essential oils by developing a slow-release layer-by-layer self-assembly for Tetranychus urticae control with selectivity toward its natural enemy

Nanoformulations containing essential oils (EOs) with oppositely charged biopolymers have gained recognition in arthropod pest management due to their biocompatibility and biodegradability. In this study, we formulated nanoemulsions (NEs) and nanocapsules (NCs) containing EO from Piper mikanianum (PMEO) using the Layer-by-Layer (LbL) method, with alternating layers of chitosan (NCs–PMEO–LbL₁) and sodium alginate (NCs–PMEO–LbL₂), for use in the management of the two-spotted spider mite, Tetranychus urticae. The PMEO yield was 0.9 ± 0.3 %, with epicyclocolorenone, germacrone, and 4,6-dimethyl-5-vinyl-1,2-benzodioxane identified as major compounds. Apparent hydrodynamic diameters were 174 ± 86 nm for NCs–PMEO–LbL₁ and 170 ± 30 nm for NCs–PMEO–LbL₂. Surface potential inversion of the NCs confirmed successful layer deposition, and the system demonstrated stability. Maximum incorporation efficiency ranged from 51.1 ± 6.0 % (NCs–PMEO–LbL₂) to 36.6 ± 4.7 % (NCs–PMEO–LbL₁). PMEO, NE-PMEO, and NCs–PMEO–LbL₂ exhibited topical toxicity to adults of T. urticae, achieving 89–97 % mortality. These formulations, including NCs–PMEO–LbL₁, reduced the egg viability of T. urticae and induced mite repellency on treated strawberry leaflets. Additionally, NCs-PMEO minimized or prevented phytotoxicity in strawberries leaflets compared to free EO. Ecotoxicological assessments revealed NCs-PMEO selectivity with Neoseiulus californicus, a predator of T. urticae, in persistence assays of biological activity. This study presents a cost-effective, solvent- and synthetic polymer-free approach to producing NCs as an eco-friendly bioacaricide for T. urticae control, offering a promising alternative to conventional synthetic acaricides.