Mutations associated with diamides resistance in lab-selected strains and field-collected populations of Plutella xylostella (Lepidoptera: Plutellidae)

Insecticide resistance in Plutella xylostella (Linnaeus) (Lepidoptera: Plutellidae) is the major constraint for the production of cruciferous crops globally. Seven populations of P. xylostella were collected from major cruciferous growing areas in Taiwan. Further, a susceptible strain of P. xylostella (SH_ggt) was selected against chlorantraniliprole and tetraniliprole under laboratory conditions to get CHL_sel and TET_sel strains, respectively. The resistance level to chlorantraniliprole and tetraniliprole and mutation frequencies of the ryanodine receptor (PxRyR) gene in these field populations and both selected strains were determined. After resistance development, both lab-selected strains and a field population were reared without exposure to insecticides and analyzed the decline of resistance and mutation frequencies. The resistance ratio (RRs) for the field-collected populations was 4.5–683.0-fold for chlorantraniliprole and 12.6-5,871.1-fold for tetraniliprole, respectively. Similarly, continuous selection to 30 generations resulted in the development of the RRs 7,073.2-fold and 6,971.0-fold for CHL_sel and TET_sel strains, respectively. Among the five investigated mutations in PxRyR, two mutations (I4790K and G4946E) were detected in field populations and only I4790K was detected in both lab-selected strains. P. xylostella populations reared without exposure to any insecticide resulted in a decline in RRs and mutation frequencies. These results imply the potential correlation between insecticide use history and target-site mutation, which can be used as a basis to develop effective strategies for diamide resistance management in P. xylostella and other insects in the fields.