Study On The Effects Of Sublethal Dosage Of Methylthio-Diafenthiuron To Plutella Xylostella

Plutella xylostella is a kind of worldwide migratory pests which mainly harms cruciferous vegetables,this pest has great impact on the quality of vegetables.The main control measurement of this pest is spraying chemical pesticides.However,drug resistance maybe serious because of the lack of standardization on pesticide application methods and dosage in addition to the high reproductive rate,the large number of generations,and the serious overlapping of generations of Plutella xylostella.In order to prevent Plutella xylostella,this study investigated a new type of medicament called Methylthio-Diafenthiuron and compared the indoor toxicity of Methylthio-Diafenthiuron to Plutella xylostella with toxicity of several common insecticides,and take a study on the sub lethal effect of Methylthio-Diafenthiuron on Plutella xylostella,then screened out insecticide synergist for controlling Plutella xylostella,study on the effects of sublethal dosage of Methylthio-Diafenthiuron on the activities of detoxification enzymes and ATPase in Plutella xylostella.Results are shown as follows:By dip method,toxicity of Methylthio-Diafenthiuron and six kinds of common insecticides to the third larvae of Plutella xylostella,and the results shown that LC₅₀ of Methylthio-Diafenthiuron is 38.5019 mg/L,the toxicity is higher than the traditional thiourea insecticide Diafenthiuron.Amide pesticide has the highest toxicity with LC₅₀ 0.4098 mg/L,and the second is abamectin benzoate with LC₅₀ 1.2429 mg/L.Toxicity of Methylthio-Diafenthiuron is lower than that of lambda-cyhalothrin and indoxacarb,and higher than chlorpyrifos.Methylthio-Diafenthiuron can be used for the prevention to Plutella xylostella.Research finds that Methylthio-Diafenthiuron can significantly affect the growth and development of Plutella xylostella.With the increase of dose,the larval stage of the pupal stage and the first generation of Plutella xylostella were significantly extended,and the pupal stage was prolonged by 29.33 hours compared with control groups,and the larval period of the first generation has been extended for 2.55 days.The sublethal concentration of Methylthio-Diafenthiuroncan decrease the pupal weight of Plutella xylostella,and significantly reduce the emergence rate of pupa,LC₃₀ concentration treatment has the lowest pupal weight which reduced for 0.41 mg compared with the control groups,and the eclosion rate decreased by 47.30%.In addition,with the increase of the low lethal concentration of Methylthio-Diafenthiuron,the number of eggs per female was decreased,and the hatching rate of Plutella xylostella was decreased,by the same time,the number of eggs per female by LC30 concentration treatment was 115.4,42.4 lower than 157.6 of control groups,the egg hatchability was also reduced by nearly 20%.Although Plutella xylostella was treated by the sub lethal concentration of Methylthio-Diafenthiuron,pupation rate of parental generation was not significantly affected,and pupation rate of parental generation did not affect the adult period.In order to improve the control effect of Methylthio-Diafenthiuron on Plutella xylostella,the effect ratio and synergism ratio of DEM,TPP,PBO on the prevention of Methylthio-Diafenthiuron by dip method.These 3 kinds of synergist improved the effect ratio in varying degrees.The optimum proportion of Methylthio-Diafenthiuron with DEM,TPP,PBO were 1:5,1:5 and 1:4,and the synergism ratio were 1.61,2.11 and 2.39.And the ratio of the synergism was 1.27,1.47 and 1.38 at the optimum ratio.In this study,the effect of the LC₃₀0 and LC₁₀ of Methylthio-Diafenthiuron on the detoxification enzymes of third larvae from 6 hours to 72 hours.The result shown that the detoxification enzymes of third larvae was induced orderedly by Methylthio-Diafenthiuron.6hours after treatment,activity of glutathione-S-transferase and ODM were suppressed in Plutella xylostella pests,and activity of carboxylesterase was increased.12 hours after treatment,activity of glutathione-S-transferase,ODM and carboxylesterase were all suppressed.72 hours after treatment,activity of glutathione-S-transferase and O DM showed no difference compared with control groups,but the activity of carboxylesterase was significantly lower than the control group.Three kinds of ATPases in larvae of Plutella xylostella were all significantly lower than that of the control groups after the treatment with Methylthio-Diafenthiuron,and the inhibition rate of Na-K-ATPase,Ca-ATPase and Ca-Mg-ATPase in group 10 mg/L were20.07%,14.64%and 10.51%.The inhibition rate in group 100mg/L were 27.13%,30.59%and 19.49%.Campared to Diafenthiuron,The Methylthio-Diafenthiuron has no phytotoxicity on cabbage and rape.The Inhibition rate of Methylthio-Diafenthiuron is-1.23%⁴.57%.The Inhibition rate of Diafenthiuron is 5.80%¹8.32%,Methylthio-Diafenthiuron is more safer.