Insecticide binding mode analysis and biological effects of acetylcholinesterase target-site resistance mutations in Spodoptera frugiperda

It is urgent to solve insecticide resistance issues for fall armyworm (FAW), Spodoptera frugiperda. Some acetylcholinesterase-1 (Ace-1) mutations (A201S, G227A and F290V) have been identified as a cause of FAW resistance to organophosphates (OPs) and carbamates insecticides (CXs). However, the structural biological mechanisms on the relationship between the Ace-1 mutations and resistance to OPs and CXs still remain elusive. In this study, the A201S and F290V mutaions were found in eight fields populations of FAW except the G227A. Molecular docking revealed that the four Ace-1 proteins (Ace1-WT, Ace1-A201S, Ace1-G227A and Ace1-F290V) had the same binding modes and the same binding energies with acetylcholine (Ach), trichlorfon, chlorpyrifos, methomyl, carbaryl and chlorpyrifos oxide. The structural biological analysis revealed that the A201S mutations can enhance enzyme catalytic efficiency by introducing the hydroxyl group (-OH) from serine which performed the same function as the main-chain -NH and enhanced the interaction with the carboxy oxygen of acetylcholine (Ach), and the F290V mutation can effectively improve FAW resistance to insecticides by increasing the likelihood of Ach to enter the enzyme's active center for phenylalanine replaced by smaller valine under insecticide inhibition conditions. The bioassays and age-stage-specific life table analysis of FAW-SS and FAW-F290V populations revealed that F290V mutation effectively contributed to FAW resistance with a low fitness cost. This study provides a theoretical basis for future pest resistance management.