Monitor And Resistance Selection Of Diamondback Moth(Plutella Xylostella)to Pyridalyl In China

Pyridalyl is a new type of insecticide with significant control effect against the diamondback moth,Plutella xylostella(L.)(Lepidoptera:Plutellidae).However,the mode of action of pyridalyl remains unclear.In order to evaluate the resistance status of pyridalyl against Plutella xylostella in China and to reveal the mode of action of pyridalyl,the susceptibility of 16 Plutella xylostella was monitored during 2013-2017.At the same time,the XY-PR strain was selected with pyridalyl under laboratory conditions.The cross resistance spectrum of pyridalyl against Plutella xylostella was studied using resistance strain,and the synergistic effects of various synergists to pyridalyl were studied,and then the resistance mechanism were predicted.The susceptibility of 16 field population to pyridalyl was different,with a median lethal concentration(LC50 value)ranging from 1.573 to 1652 ppm.It can be seen that the population of Plutella xylostella in the south of China has a high resistance to pyridalyl,while the resistance of Plutella xylostella to pyridalyl is relatively moderate and low in the central and northern regions of China.After 10 generations of selecting with pyridalyl,the resistant XY-PR strain was obtained.The selected XY-PR strain displayed 32-fold resistance to pyridalyl compared to the XY-PS strain.The XY-PR strain did not display cross resistance to avermectin,emamectin benzoate,chlorfenapyr and chlorantraniliprole,but showed 40-fold cross resistance to fipronil.On the other hand,ZL-PR strain showed high cross resistance to the above insecticides.This suggests that Plutella xylostella is easy to develop resistance to pyridalyl in laboratory conditions.Plutella xylostella of continuously selected with pyridalyl is susceptible to cross resistance with fipronil,this two pesticides are not suggested to be used at the same time.In the XY-PR strain,PBO showed 5.8-fold synergistic effect to pyridalyl,while DEM and TPP did not show significant synergistic effect against pyridalyl;in the ZL-PR strain,PBO,DEM,and TPP did not show significant synergism.The synergist experiments showed that the resistance of XY-PR strain to pyridalyl may be related to the enhanced detoxification metabolic capacity of multifunctional oxidases,while ZL-PR strain may have different resistance mechanisms compared to the XY-PR strain.