Stability, Inheritance, Cross-Resistance, and Fitness Cost of Resistance to λ-Cyhalothrin in Cydia pomonella

Insecticides are commonly utilized in agriculture and forestry for pest control, but their dispersal can pose hazards to humans and environment. Understanding resistance, inheritance patterns, and fitness costs can help manage resistance. A λ-cyhalothrin-resistant population (LCR) of Cydia pomonella, a global pest of pome fruits and walnuts, was obtained through selective insecticide breeding for 15 generations, showing stable moderate resistance (23.85-fold). This population was cross-resistant to deltamethrin (4.26-fold) but not to β-cypermethrin, chlorantraniliprole, chlorpyrifos, and avermectin. Genetic analysis revealed the resistance was autosomal, incompletely dominant, and controlled by multiple genes. Increased activity of glutathione S-transferases and cytochrome P450 monooxygenases (P450s) played a primary role in resistance, with specific genes up-regulated in LCR, and exhibited significant expression in midgut. LCR also exhibited fitness costs, including delays in development, reduced fecundity, and slower population growth. These findings contribute to understanding λ-cyhalothrin resistance in C. pomonella and can guide resistance management strategies.