Chemical Composition and Repellent Activity of Strobilanthes tonkinensis Foliar Extract and Its Fractions Against Tribolium castaneum.

Protecting stored grains from pest infestation (e.g., Tribolium castaneum) is crucial for cereal preservation and food safety. The insecticides commonly used for grain storage can leave toxic residues or byproducts that pollute the environment and harm humans. In this study, the repellent activity of natural products from Strobilanthes tonkinensis Lindau leaves against T. castaneum was investigated. Thirty-five chemical components were tentatively identified, and the repellent activities of the crude extract, its fractions, and estragole were evaluated. At the same concentrations (1%, equivalent to 10 mg/mL or 157.27 µg/cm2), the extracts (after 16 and 24 h of exposure) and Fraction 1 (after 6 h of exposure) exhibited repellency comparable to that of the positive control (DEET) against T. castaneum adults. The repellent activity and mechanism of estragole, a constituent of Fraction 1, were further investigated. The results indicated that estragole exerted dose- and time-dependent repellent effects. Moreover, similar to the commercial repellent DEET, estragole significantly upregulated the expression of the odorant-binding protein TcOBPC11 and chemosensory protein TcCSP9. In conclusion, natural products derived from S. tonkinensis leaves, including both the extracts and specific compound estragole, showed promising repellent activities, suggesting their potential as alternative agents for the management of T. castaneum.