Cross-resistance, biochemical mechanism and fitness costs of laboratory-selected resistance to pyridalyl in diamondback moth, Plutella xylostella.

Pyridalyl belongs to one novel type of insecticides with uncertain mode of action, and it showed significant efficacy against Plutella xylostella, which has been considered as one notorious insect pest in the world. To characterize pyridalyl resistance in P. xylostella, one susceptible strain XY-PS and one laboratory-selected pyridalyl-resistant strain XY-PR (34.4-fold) were used to establish cross-resistance patterns, and no cross-resistance to a series of popular insecticides in the XY-PR was observed. Activities of metabolic enzymes were measured and results showed that there was an approximate 5.2-fold significant increase in cytochrome P450 monooxygenase (P450) and no significant differences in glutathione S-transferase (GST) and esterase between XY-PR and XY-PS, indicating that the enhanced activity of P450 could be dominant mechanism of detoxification. Furthermore, expression profiles of three previously published resistance-associated P450 genes were established but no one was significantly different expression. Besides, fitness costs associated with pyridalyl resistance was observed in XY-PR, and it had been found that survival rate of larvae and hatchability were reduced in XY-PR. Then, by calculating the net replacement rate (R) of XY-PS, the fitness of XY-PR was established as 0.64. In conclusion, above results provided helpful data and information for studying further on mechanism of pyridalyl resistance, and will be conductive to design rational strategies of resistance management in P. xylostella.