| Summary: | Background: The destructive insect pest <i>Agrotis ipsilon</i> (Hufnagel) (Lepidoptera: Noctuidae) is a polyphagous species targeting many economically important plants. The extensive and arbitrary use of insecticides has resulted in the build-up of insecticide resistance and pesticide residues accumulating in food. Therefore, it is becoming evident that alternative pest management tools are needed to reduce risks to humans, the environment, and non-target organisms, and at the same time, they should be used in field application at the lowest cost. Methods: In view of this objective, the present study demonstrates the toxicity of lemongrass (<i>Cymbopogon citratus</i> (DC.) Stapf) essential oil (EO), against the black cutworm <i>A. ipsilon</i> under controlled laboratory conditions in terms of measuring the activity of peroxidase and detoxification enzymes. The chemical components of the EO were analyzed using GC–MS. Results: The results show that after 96 h post treatment, the LC<sub>15</sub> and LC<sub>50</sub> values were 427.67 and 2623.06 mg/L, respectively, of <i>C. citratus</i> EO on second-instar larvae of <i>A. ipsilon</i>. A slight significance in elongation of the larval duration with LC<sub>15</sub> and LC<sub>50</sub> value was found with control. By GC–MS analysis, the main compounds identified in the EO were <i>α</i>-citral and <i>β</i>-citral with percentages of 35.91%, and 35%, respectively. The oxidative stress indicates a significant increase in CAT and lipid peroxidase enzyme activity after 96 h post treatment at the LC<sub>15</sub> and LC<sub>50</sub>. Conversely, the detoxification enzyme activity shows an inhibition of CarE and GST enzymes of larvae exposed to LC<sub>15</sub> and LC<sub>50</sub> values in response to <i>C. citratus</i> EO. Conclusions: The present data show that lemongrass EO has insecticidal activity against the black cutworm, <i>A. ipsilon</i>.
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