Insecticide resistance mechanisms and resistance risk assessment in diamondback moth (Plutella xylostella) populations

Abstract:

The diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae), is one of the most destructive insect pests of cruciferous vegetables worldwide and is characterized by a remarkable ability to develop resistance to insecticides representing diverse modes of action. The present study was designed to assess the susceptibility status, resistance mechanisms, cross-resistance patterns and resistance risk of P. xylostella populations collected from major crucifer-growing regions. Field populations were compared with a laboratory-maintained susceptible population using concentration–mortality bioassays. LC₅₀ and LC₉₅ values were estimated by probit analysis and resistance ratios were calculated relative to the susceptible population. Biochemical assays were used to investigate the activities of cytochrome P450 monooxygenases, glutathione-S-transferases (GSTs) and carboxylesterases (CarEs). Synergist bioassays were conducted to assess the contribution of metabolic detoxification, while laboratory selection was used to estimate resistance development and realized heritability. The results indicated considerable variation in susceptibility among field populations and insecticide classes. The highest resistance was observed against the diamide insecticides, particularly cyantraniliprole, whereas comparatively lower resistance was observed against selected alternative chemistries. Resistant populations exhibited elevated P450, GST and CarE activities, suggesting an important contribution of metabolic detoxification. Laboratory selection resulted in a progressive increase in LC₅₀, indicating considerable resistance risk under continuous selection pressure. The findings emphasize that resistance management in P. xylostella should integrate routine susceptibility monitoring, rotation of insecticides according to mode of action, treatment-window strategies, threshold-based applications, biological control and non-chemical tactics. Such an integrated approach is essential for preserving insecticide efficacy and achieving sustainable management of diamondback moth in cruciferous vegetable production.