Susceptibility of field populations of Spodoptera litura (Fabricius) (Lepidoptera: Noctuidae) in China to chlorantraniliprole and the activities of detoxification enzymes

Abstract

The cutworm Spodoptera litura is a major insect pest of vegetables and cotton in China, and has been reported to develop resistance to various classes of insecticides. Chlorantraniliprole, which has been registered recently in China, provides a novel option for control of this pest. The susceptibilities of S. litura collected from Southeast China to chlorantraniliprole were determined by diet incorporation assay with neonates. The susceptibility variation among 12 field populations was low (<4-fold), with median lethal concentration (LC50) values varying from 28.4 to 102.5 μg/l. However, all the 12 field populations were less susceptible to chlorantraniliprole than a laboratory susceptible population. The most tolerant populations were sampled from Guangdong and Anhui Provinces where S. litura had been frequently challenged by insecticides. However, no correlation was found between LC50 values and the number of applications of this chemical. Biochemical assays were performed to determine the potential mechanisms involved in the tolerance observed in field populations. Most field populations showed significantly enhanced activities of mixed function oxidase enzymes compared with the susceptible strain. Only a few populations had higher activities of esterase and glutathione-S-transferase than the susceptible strain. No correlations were observed between activities of metabolic enzymes and chlorantraniliprole toxicity, suggesting that these detoxification enzymes were not the main cause of the field tolerance observed in this study, and there might be other mechanisms conferring the tolerance variation to chlorantraniliprole in S. litura.