Thymol as a potential botanical insecticide against Tuta absoluta: life history parameters, toxicity and enzymatic responses

This study evaluated the insecticidal potential of thymol against the pest Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae), its effects on key physiological enzyme activities, and investigated the duration of the insect's developmental stages. Initially, the study's complete objectives and conducted experiments were detailed, including toxicity assessment via topical bioassays and the estimation of lethal doses (LD 50 ) using probit analysis. Thymol exhibited high toxicity, with a 24-h LD 50 calculated at 6.866 µg/larva. The larval development period and adult longevity were significantly reduced at LD 30 and LD 50 compared to the control, and the oviposition rate also decreased. Biochemical assays revealed substantial alterations in the activities of detoxification and antioxidant enzymes. Antioxidant enzyme activities were elevated. In contrast, detoxification enzymes, including glutathione S-transferase, α- and β-esterases, and cytochrome P450 monooxygenases, were significantly and dose-dependently decreased, as was acetylcholinesterase. Thymol was also observed to reduce sodium–potassium adenosine triphosphatase (Na⁺/K⁺ ATPase) activity. The results indicate that thymol induces toxicity through multiple physiological pathways, including disruption of detoxification systems and ionic homeostasis. These findings introduce thymol as a promising candidate for a botanical insecticide in managing the T. absoluta .