Natural biopesticide: Thymol's efficacy on beetle Tenebrio molitor

Tenebrio molitor is a key pest of stored products, and the search for sustainable control methods has led to increasing interest in plant-based insecticides. In this study, we evaluated the contact toxicity of thymol, a monoterpene extracted from Lamiaceae plants, against T. molitor larvae. A total of 1,200 fourth- and fifth-instar larvae were exposed to thymol-treated surfaces at concentrations ranging from 0 to 50 gL⁻¹. Larval mortality varied significantly among concentrations, with a clear dose-dependent response. Even at 0.1 gL⁻¹, thymol induced considerably higher mortality than the control group. Mortality rates exceeded 80% at concentrations ≥1 gL⁻¹, and most deaths occurred within the first 24 hours. The LC₅₀ and LC₉₀ values estimated for this period were 0.17 and 2.75 gL⁻¹, respectively, indicating high acute toxicity. These findings confirm thymol's potential as a fast-acting botanical insecticide for the management of stored-product pests. Future studies should investigate its efficacy under real storage conditions, long-term stability, and potential non-target effects.