Physicochemical properties, insecticidal activity, and biochemical responses of a tea saponin-stabilized Zanthoxylum bungeanum essential oil nanoemulsion against stored-product pests.

Zanthoxylum bungeanum essential oil (ZEO) is a promising botanical insecticide, but its volatility and poor water dispersibility limit practical application. This study aimed to develop a tea saponin-stabilized ZEO nanoemulsion (TS-ZEO-NE) and evaluate its physicochemical properties, insecticidal and repellent activities, enzyme responses, molecular docking, and cytotoxicity. GC-MS identified limonene (43.45%), β-pinene (14.92%), linalool (14.29%), and linalyl acetate (13.31%) as the major constituents. TS-ZEO-NE had a mean droplet size of 133.00 nm, a PDI of 0.16, and a zeta potential of -21.65 mV, with spherical droplets and good physical stability. Contact, fumigant, repellent, and simulated storage assays were conducted against Tribolium castaneum and Lasioderma serricorne. TS-ZEO-NE showed lower contact LD50 values than ZEO against adults and larvae of both species, whereas ZEO exhibited greater fumigant activity. β-Pinene, limonene, and linalool generally exhibited greater contact or fumigant activity than linalyl acetate. TS-ZEO-NE maintained stronger repellency after prolonged exposure. In simulated storage chambers, 48-h repellency reached 51.4% and 47.8% against T. castaneum and L. serricorne, respectively. Enzyme assays showed that ZEO and TS-ZEO-NE exposure decreased AChE activity and increased CarE and GST activities in both species, while SDH activity decreased in T. castaneum, with TS-ZEO-NE generally inducing greater changes than ZEO. Molecular docking of the four major ZEO constituents with selected proteins indicated relatively weak to moderate predicted interactions (-3.54 to -5.60 kcal/mol). L-929 fibroblast viability remained above 80% at 0.05-0.80 mg/mL TS-ZEO-NE. Overall, TS-based nanoemulsification improved ZEO contact toxicity and prolonged repellency, supporting its potential for stored-product pest management.