Metabolomic and partial proteomic analyses of phosphine resistance in Sitophilus oryzae adults: Significant reduction in body weight after acquiring resistance.

Fumigation with phosphine (PH), the toxicity of which is related to reactive oxygen species (ROS) generation, is widely used to control insect pests such as Sitophilus oryzae in stored commodities. However, overuse and misuse of PH fumigation have led to severe resistance in the targeted insect pests, including S. oryzae. Prior to omics studies, we determined that the differences in LC (the lethal concentration to kill 50 % of the organisms) and CT (the concentration-time to kill 50 % of organisms) values for PH between the PH-susceptible and PH-resistant strains were 23.4-fold and 11.6-fold, respectively. The point mutation (N505T) in dld responsible for encoding dihydrolipoamide dehydrogenase found in the PH-resistant strain causes it to have a significantly lower body weight than the PH-susceptible strain. The activities of three enzymes (cytochrome c oxidase, catalase and carboxylesterase), transcript levels of detoxification- and antioxidant-related gene (cyp450, gst, abcg23, cat, and pod), and ROS level were significantly downregulated in PH-resistant S. oryzae, while histidine metabolism, Coenzyme A biosynthesis, and ascorbate and aldarate metabolism were significantly upregulated in the PH-susceptible strain. In the metabolomics analysis of the PH-resistant strain, 39 significant metabolites with p-value <0.05 and fold change >2 (including mannose-6-phosphate, spermine, aconotic acid, spermidine, and phenylalanine) were identified, while fumaric acid and lactose levels were significantly reduced. In conclusion, S. oryzae overcomes PH toxicity via a variety of metabolic processes, especially ROS-induced oxidative stress.