Inheritance and fitness costs of resistance to Bacillus thuringiensis toxin Cry2Ad in laboratory strains of the diamondback moth, Plutella xylostella (L.).

The diamondback moth, Plutella xylostella (Lepidoptera: Plutellidae), is one of the main pests of Brassica crops worldwide. Management of P. xylostella is particularly challenging, as different field populations have readily acquired resistance to a wide range of insecticides, including Bacillus thuringiensis (Bt) toxins. In this study, a novel strain of P. xyllostela (Fuzhou-R2Ad) with 120-fold resistance to Bt Cry2Ad was selected in the laboratory, after screening for 66 generations from the susceptible strain Fuzhou-S. In the absence of Bt Cry2Ad toxin, the Fuzhou-R2Ad had significantly lower fitness as compared to the susceptible strain, which might be related to induced genetic changes to Bt toxins. We used several models to measure the dominance levels of insecticide resistance among different strains and found an incompletely recessive inheritance pattern of the Fuzhou-R2Ad resistance, which might be controlled by multiple genes. This study constitutes the first report of laboratory-acquired resistance to Cry2Ad toxin in P. xylostella. Our work presents further insights into the mechanism of Bt resistance and has immediate implications for the integrated pest management of P. xylostella globally.