Realized heritability, mode of inheritance, and fitness costs of Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae) resistance to chlorantraniliprole.

The cotton leafworm, Spodoptera littoralis (Boisd.) (Lepidoptera: Noctuidae), is an economically important pest in Egypt. This study examines the inheritance patterns, potential for resistance development, and fitness costs associated with chlorantraniliprole (CHL) resistance in S. littoralis. Laboratory selection over 15 generations resulted in a substantial resistance level, with a resistance ratio of 402.85-fold. Genetic analysis, including reciprocal crosses and backcrosses, revealed that CHL resistance is autosomal, polygenic, and exhibits incomplete dominance. The estimated realized heritability (h²) of resistance was 0.37, indicating a considerable potential for resistance development under selection pressure. Fitness assessments revealed no significant reproductive penalties associated with resistance; however, the resistant strain exhibited a significant developmental delay in the larval and pre-adult stages. These findings suggest that CHL resistance can rapidly evolve and persist in field populations, thereby complicating control efforts. The polygenic inheritance pattern underscores the complex genetic mechanisms underlying resistance, necessitating integrated management strategies. The reduced fitness costs further emphasize the importance of implementing proactive resistance management, such as rotating insecticides with different modes of action and integrating nonchemical control measures, to sustain the efficacy of CHL. Overall, this study provides critical insights into the genetic and biological dynamics of CHL resistance in S. littoralis, underscoring the urgency of vigilant resistance monitoring and strategic control practices to mitigate resistance and prolong the utility of CHL in pest management programs.