| Summary: | <i>Tuta absoluta</i> is a major pest, damaging tomato crops in many countries. Spinetoram, a novel insecticide, is increasingly used for the management of various insect pests. However, limited information is available on its lethal effects on <i>T. absoluta</i>. Therefore, this study was carried out to evaluate the toxicity of spinetoram concentrations in <i>T. absoluta</i> by exposing third-instar larvae to this insecticide through leaf-dipping bioassays under laboratory conditions. The results showed that sublethal spinetoram concentrations (LC<sub>10</sub> and LC<sub>20</sub>) extended the developmental duration of the larval and pupal stage, as well as the oviposition period, and decreased the pupal weight, pupation and eclosion rates, fecundity, sex ratio, and egg-hatching rate compared to the control group. LC<sub>10</sub> and LC<sub>20</sub> treatments up-regulated the activity of superoxide dismutase and catalase antioxidant enzymes in <i>T. absoluta</i> larvae by 51.14–88.72% and 39.34–87.76% at 12 h, 62.71–96.68% and 37.38–39.92% at 24 h, and 41.78–53.34% and 19.44–48.39% at 48 h, respectively, compared to the control. Conversely, the LC<sub>10</sub> and LC<sub>20</sub> treatments inhibited the activities of detoxifying enzymes, i.e., carboxylesterase (14.72–34.95%), acetylcholinesterase (9.02–48.86%), glutathione S-transferase (19.40–43.19%), and mixed-function oxidase (18.18–25.93%). These findings indicate that lethal concentrations of spinetoram influence the population dynamics of <i>T. absoluta</i> by reducing their survival and developmental potential and inhibiting the activity of detoxifying enzymes.
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