Studies On The Resisitance Status And Resistance Mechanisms To Insecticides Of The Diamondback Moth(Plutella Xylostella) In Shaanxi Province

Diamondback moth(DBM)(Plutella xylostella.L)is one of the most destructive pest of cruciferous vegetables in China and elsewhere in the world.Managemnt of DBM has mainly relyied on chemical insecticides.Field-evolved resistnace to these insecticides of DBM populations has been a major concern for effective control of this damaging pest in the vegetable-growing regions in China.Cruciferous vegetables are planted in three different regions in shaanxi province,but the resistance status to nine currently-available insecticides,including abamectin,a-cypermethrin,diafenthiuron,chlorfluazuron,chlorfenapyr,indoxacarb,spinosad,chlorantraniliprole and the insecticidal protein Cry1Ac from Bacillus thuringiensis(Bt)of the field populations of DBM from the three vegetaible-growing regions and their resistance mechanisms remain largely known.To address these questions,I collected DBM field populations from the three regions,tested their resistance levels by bioassays,and determined their resistance mechanisms by synergism bioassays and enzymatic analyses.The main research results are as followsThe sensitivities to the nine insecticides of DBM field populations collected in 2012 and 2013 from three different representative vegetable-growing regions(Yangling,Baoji and Weinan)of shaanxi province were determined by the dose-response line bioassay and the discriminating dose bioassay in laboratory.The results showed that the DBM field populations collected from the three different regions during the last two years(2012-2013)have developed different levels of resistance to most of the nine insecticides.The Baoji,Weinan and Yangling populations have developed high to very high levels of resistance to a-cypermethrin,moderate to high levels of resistance to abamectin,low to moderate levels of resistance to chlorfenapyr and chlorfluazuron,and none to low levels of resistance to indoxacarb,spinosad and chlorantraniliprole.There were large differences in resistance ratios to Bt and diafenthiuron among the field populations from the three regions.Decreased sensitivity,low to moderate and moderate resistance to diafenthiuron were observed in Baoji,Yangling and Weinan populations,respectively.Yangling and Weinan populations displayed decreased sensitivity or low levels of resistance to Bt,whereas Baoji populations exhibited moderate levels of resistance to Bt.Use of a-cypermethrin and abamectin should be paused because high levels of resistance to these two insecticides have been detected in the field populations from all the three representative regions.The number of applications should be reduced for those insecticides,to which field populations of DBM have developed moderate levels of resistance.The insecticides to which field populations of DBM remain susceptible or only have low levels of resistance can be used as the main compounds to manage DBM populations.Furthermore,insecticides should be alternatively used to delay the development of resistance of DBM to these insecticides.Synergism bioassays of the susceptible lab strain and the resistant field population fromBaoji(called baoji population hereafter)with PBO(a MFO inhibitor),TPP(a CarE inhibitor)and DEM(a GST inhibitor)showed that none of the three inhibitors had synergistic effects on the toxicity of abamectin against the susceptible strain.By contrast,combinational use of PBO and TPP with abamectin against Baoji population resulted in 50%and 12.5%increase in mortality respectively,relative to the mortality of abamectin alone.While TPP and DEM did not increase the mortality of a-cypermethrin against the susceptible strain,they caused 52.5%and 15%mortality increase,respectively,against Baoji population.PBO significantly increased the mortality of a-cypermethrin against both the susceptible strain and the resistant Baoji population,but its synergistic effects were significantly greater against Baoji population than against the susceptible strain.Enzymatic analyses revealed that the total enzyme activities of MFO and CarE were 2.31 and 3.39 times higher in Baji population than in the susceptible strain.No significant difference was observed in the total enzyme activity of GST between the two populations.Taken together,these data suggest that enhanced MFO-and CarE-mediated metabolism of abamectin as well as enhaced MFO-,CarE-and GST-mediated metabolism of ?-cypermethrin are at least partially responsible for resistance of Baoji population to the two insecticides.