Influence of seasonal migration on evolution of insecticide resistance in Plutella xylostella

The diamondback moth, Plutella xylostella (L.), is one of the most destructive migratory pest species of cruciferous vegetables worldwide and has developed resistance to most of the insecticides used for its control. The migration regularity, migratory behavior, and relationship between flight and reproduction of P. xylostella have been widely reported. However, the effect of migration on insecticide resistance in this pest is still unclear. In this study, the effect of migration on P. xylostella resistance to seven insecticides was investigated using populations across the Bohai Sea that were collected in the early and late seasons during 2017-2019. The bioassay results showed that the early season populations of P. xylostella from south China possessed much higher resistance to insecticides because of intensive insecticide application; alternatively, the late season populations migrated from northeast China, where the insecticides were only used occasionally, showed much lower insecticide resistance. The genome re-sequencing results revealed that, among the eight mutations involved in insecticide resistance, the frequencies of two acetylcholinesterase mutations (A298S and G324A) responsible for organophosphorus insecticide resistance were significantly decreased in the late season populations. The results indicated that P. xylostella migration between tropical and temperate regions significantly delayed the development of insecticide resistance. These findings illustrated the effect of regional migration on the evolution of insecticide resistance in P. xylostella, and provided foundational information for further research on the relationship between migration and insecticide resistance development in other insects.