Background: The destructive insect pest Agrotis ipsilon (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 (Cymbopogon citratus (DC.) Stapf) essential oil (EO), against the black cutworm A. ipsilon 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 LC₁₅ and LC₅₀ values were 427.67 and 2623.06 mg/L, respectively, of C. citratus EO on second-instar larvae of A. ipsilon. A slight significance in elongation of the larval duration with LC₁₅ and LC₅₀ value was found with control. By GC–MS analysis, the main compounds identified in the EO were α-citral and β-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 LC₁₅ and LC₅₀. Conversely, the detoxification enzyme activity shows an inhibition of CarE and GST enzymes of larvae exposed to LC₁₅ and LC₅₀ values in response to C. citratus EO. Conclusions: The present data show that lemongrass EO has insecticidal activity against the black cutworm, A. ipsilon.

Background: Spodoptera littoralis (Boisd.) is a prominent agricultural insect pest that has developed resistance to a variety of insecticide classes. In this study, the resistance of three field strains of S. littoralis, collected over three consecutive seasons (2018 to 2020) from three Egyptian Governorates (El-Fayoum, Behera and Kafr El-Shiekh), to six insecticides was monitored. Methods: Laboratory bioassays were carried out using the leaf-dipping method to examine the susceptibility of the laboratory and field strains to the tested insecticides. Activities of detoxification enzymes were determined in an attempt to identify resistance mechanisms. Results: The results showed that LC₅₀ values of the field strains ranged from 0.0089 to 132.24 mg/L, and the corresponding resistance ratio (RR) ranged from 0.17 to 4.13-fold compared with the susceptible strain. Notably, low resistance developed to spinosad in all field strains, and very low resistance developed to alpha-cypermethrin and chlorpyrifos. On the other hand, no resistance developed to methomyl, hexaflumeron or Bacillus thuringiensis. The determination of detoxification enzymes, including carboxylesterases (α- and β-esterase), mixed function oxidase (MFO) and glutathione-S-transferase (GST), or the target site of acetylcholinesterase (AChE), revealed that the three field strains had significantly different activity levels compared with the susceptible strain. Conclusion: Our findings, along with other tactics, are expected to help with the resistance management of S. littoralis in Egypt.