Encapsulation of Satureja hortensis L. (Lamiaceae) in chitosan/TPP nanoparticles with enhanced acaricide activity against Tetranychus urticae Koch (Acari: Tetranychidae)

Abstract

The objective of this study was the fabrication of encapsulated Satureja hortensis essential oil (S.EO) in chitosan/tripolyphosphate nanoparticles (CS/TPP-NPs) via ionic gelation technique and investigation of its acaricidal effect. A high encapsulation efficiency of 96.17% was obtained, which shows successful encapsulation of EOs in CS-TPP nanoparticles. Transmission electron microscopy (TEM) analysis proved the formation of spherical S. hortensis EO-loaded chitosan nanoparticles (S.EO@NPs). Fourier-transform infrared spectroscopy (FTIR) analysis demonstrated the presence of encapsulated S.EO in CS/TPP nanoparticles. The average size of nanoparticles was found to be 192.1 ± 11 nm using dynamic light scattering (DLS) technique. Moreover, durability and fumigant acaricide activity of S.EO@NPs against Tetranychus urticae Koch were investigated. The obtained results demonstrated that there were considerable differences between pure S. hortensis EO and S.EO@NPs in their ovicidal, adulticidal, and persistence activities against T. urticae. The LC₅₀ values of pure EO and as-prepared S.EO@NPs against adult mite were 4.95, 46.98 µL/L after 24 h exposure and 2.02, 31.30 µL/L after 72 h exposure, respectively. Fumigation exposure for 24 and 72 h showed that the sensitivity of adults T. urticae were more than the eggs of T. urticae. The LC₅₀ values of fumigant toxicity of pure S.EO and S.EO@NPs against eggs of T. urticae were measured after 24 and 72 h. The experimental results for 24 h treatment showed 6.71 and 211.66 µL/L air LC₅₀ values for pure S.EO and S.EO@NPs, respectively. In the case of 72 h exposure, The LC₅₀ values of pure S.EO and S.EO@NPs were 4.15 and 107.38 µL/L air, respectively. A sustained release of S.EO from S.EO@NPs was observed during 25 days of the study, indicating the persistence acaricide activity for a long time. The as-prepared S.EO@NPs and pure S.EO illustrated 67% and 2% mortality at 18th day exposure, respectively. The notable increasing of the residual fumigant toxicity may be related to the slow and sustainable release of the active ingredient of EO. Based on this study, the S.EO@NPs showed significantly residual adulticidal activity against adults of T. urticae. S.EO@NPs would be recommended as an alternative for pure EOs and other common acaricides.

Keywords: Acaricide; Chitosan; Nanoparticle; Persistence fumigant toxicity; Satureja hortensis essential oil.