Biochemical Characterization and Insecticide Susceptibility of Two Egyptian Field Strains of Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae)

Fall armyworm (FAW) Spodoptera frugiperda ( S. frugiperda ) represents a major threat to cereal crops, particularly maize. This study aimed to evaluate the susceptibility of the second‐instar larvae from two Egyptian field strains of S. frugiperda to ten insecticides, comparing them with a susceptible laboratory strain. The laboratory strain demonstrated high susceptibility to bioinsecticides such as emamectin benzoate and spintoram (LC 50 = 0.003 mg/L), followed by spinosad (LC 50 = 0.01 mg/L). New chemical insecticides, including cyantraniliprole, chlorantraniliprole, and indoxacarb, exhibited moderate toxicity to the laboratory strain, with LC 50 values of 0.02, 0.19, and 0.26 mg/L, respectively. In contrast, conventional insecticides showed very low toxicity. Field populations from Giza (G) and Bani‐Sewif (BS), Egypt, were assessed for susceptibility. Resistance monitoring revealed that the Giza population displayed high resistance to indoxacarb, cyantraniliprole, and spinosyns (spinosad and spintoram), whereas the BS population exhibited high resistance only to spinosad. Additionally, significantly elevated levels of carboxylesterase (α and β‐esterase), cytochrome P450, glutathione S‐transferase (GST), and AChE were observed in the Giza population, whereas no significant differences were found in the BS population. This study illuminates a prominent resistance mechanism and underscores the need for tailored pest management strategies based on regional resistance profiles and biochemical characteristics.