Resistance of Egyptian Field Populations of Spodoptera littoralis (Lepidoptera: Noctuidae) to Emamectin Benzoate and Role of Detoxification Enzymes

Background: One of the most significant pests that harm numerous agricultural crops ‎is the cotton leafworm Spodoptera littoralis (Boisduval) and it has evolved resistance ‎to various insecticides across most chemical classes, including the novel insecticide ‎emamectin benzoate. ‎Methods: The sensitivity of emamectin benzoate was evaluated in Egyptian cotton ‎leafworm field populations. ‎Results: According to bioassays performed using the leaf-dipping method, emamectin ‎benzoate sensitivity varied among 5 field populations, with LC50 values ranging from ‎‎2.78 to 6.86 ppm. Two S. littoralis populations demonstrated the low levels of ‎resistance at resistance ratios (RR) between 17.9- and 22.3-fold and three populations ‎showed moderate resistance at 33.5 to 42.8-fold compared with a susceptible ‎population. The findings demonstrated that diethyl maleate (DEM) and piperonyl ‎butoxide (PBO) have considerable synergistic effects on the toxicity of emamectin ‎benzoate. ‎Conclusion: The results suggest that emamectin benzoate resistance in the S. littoralis ‎populations studied may be caused by the enzyme systems monooxygenase (MO) and ‎glutathione S-transferase (GST).‎Highlights‎Emamectin benzoate efficacy is decreasing in populations of Spodoptera littoralis.‎‎Emamectin benzoate resistance in littoralis field populations ranges from low to ‎moderate. ‎‎The field populations’ monooxygenase and glutathione S-transferase activity were ‎higher than those of the susceptible population‎.