Biochemical and molecular characterization of chlorantraniliprole resistance in Spodoptera littoralis (Lepidoptera: Noctuidae)

Resistance is one major problem that reduces the efficacy of insecticides against insect pests. Understanding the biochemical and molecular foundations of insect resistance to insecticides can help achieve the objectives of insect control and resistance management. In this study, resistance to chlorantraniliprole was developed in a field strain of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) over fifteen generations using the selection pressure. In addition, the biochemical basis of resistance and cross-resistance to other insecticides were investigated. Moreover, the expression of esterase and Cytochrome P450 (CYP450) genes was quantitatively estimated in S. littoralis on exposure to chlorantraniliprole by using real-time PCR. The LC50 values of chlorantraniliprole to the developed resistant strain (CHL-R) and the susceptible strain (Sus) were 2.256 and 0.0056mg/L (ppm), respectively, representing a resistance ratio (RR) of 402.85. The CHL-R strain showed no cross-resistance to chlorpyrifos, methomyl, lambada-cyhalothrin, emamectin benzoate, and spinetoram (RR ranged from 0.97 to 1.89). However, a low cross-resistance level was developed to methoxyfenozide (RR = 4.04) and a moderate level was developed to indoxacarb (RR = 30.83). Synergism assays suggested that CYP450 may be involved in resistance development in the CHL-R strain. Nevertheless, a significant decrease in Carboxylesterases (CarE) and Glutathione S-transferase (GST) activities was observed. Consistently, over-expression of the CYP450 gene was recorded in the CHL-R strain, which provides a foundation for understanding the mechanism of S. littoralis resistance to chlorantraniliprole in Egypt. Generally, our results provide valuable information for monitoring and managing S. littoralis resistance in Egypt.