Preliminary Study On Sublethal Effect And Detoxification Metabolism Of Three Insecticides On Spodoptera Frugiperda

The fall armyworm（FAW）,Spodoptera frugiperda（J.E.Smith）（Lepidoptera:Noctuidae）is an important invasive agricultural pest.At present,the main method to control FAW is chemical control.In order to determine the effects of metaflumizone,indoxacarb and spinetoram on the population of FAW,the effects of sublethal concentrations of LC₁₀ and LC₃₀ on the growth and reproduction of F₀ and F₁ generations of FAW were studied by the amphoditic life table method.The synergies of enzyme inhibitors on the third instar larvae of FAW were measured.In addition,the activity of carboxylesterase（Car E）,glutathione S-transferase（GST）and mixed-function oxidases（MFO）were measured under the sublethal concentration.The main research results are as follows:1.Determination of sublethal doses of three insecticides and their effects on development and reproduction of F₀ and F₁generations of S.frugiperdaThe toxicity levels of metaflumizone,indoxacarb and spinetoram against the third instar larvae of FAW were determined by artificial feed toxicity mixing method,and the effects of sublethal concentrations(LC₁₀ and LC₃₀)of metaflumizone,indoxacarb and spinetoram on survival,growth and reproduction ability of FAW were studied.The results showed that the effects of sublethal concentrations of metaflumizone,indoxacarb and spinetoram on survival,growth and reproduction of FAW.According to the toxicity test results,the LC₁₀ values of metaflumizone,indoxacarb and spinetoram against FAW were 0.733 mg/kg,5.989 mg/kg and 0.031 mg/kg,respectively,and the LC₃₀values were 1.489 mg/kg,10.163 mg/kg and0.066 mg/kg,respectively.The study revealed that the pupal stages of FAW in both F₀ and F₁ generations had a prolonged developmental duration after being treated with LC₁₀ and LC₃₀ concentrations.Meanwhile,the lifespan and spawning period of female adults of F₀and F₁ generations shortened significantly compared with the control.During the F₀ and F₁generations,there was a notable decrease in both the number of eggs laid and the hatching rate.The pupation rate,pupa weight and emergence rate of F₀ generation were all decreased,but there was no significant difference in emergence rate between treatment group and control group.The larval stage of F₁ generation was prolonged significantly and increased with the increase of the concentration of the insecticides.Compared with the control group,the 5th and 6th instar larvae stages of F₀ generation were shortened at the concentrations of metaflumizone and indoxacarb LC₁₀ and LC₃₀,while the 4th,5th and 6th instar larvae stages of F₀ generation were prolonged at the concentrations of indoxacarb and LC₃₀.The intrinsic growth rate（r_m）,the peripheral growth rate（λ）and the net growth rate（R₀）were significantly decreased after the treatment of sublethal concentrations of the three insecticides,and the average generation period（T）was significantly prolonged,and increased with the increase of the concentration of the three insecticides.Sublethal concentrations of metaflumizone,indoxacarb and spinetoram affected the growth,development and reproduction of FAW and inhibited its population growth.2.Synergistic effects of synergists on three insecticides treated with third instar larvae of S.frugiperdaBefore conducting the toxicity test,corn leaves were impregnated with 100 mg/kg of triphenyl phosphate（TPP）,diethyl maleate（DEM）,and piperonyl butoxide（PBO）for phenyl phosphate.After 12 hours of feeding the third instar larvae of FAW,toxicity was determined using the artificial feed poisoning method.The control group was fed corn leaves without synergistic impregnation.The study aimed to determine the synergistic effects of TPP,DEM,and PBO on metaflumizone,indoxacarb and spinetoram.According to the study,the synergistic effect of TPP,DEM,and PBO on metaflumizone was found to be less than1.20 times when applied to third instar larvae.Additionally,the LC₅₀ value was not significantly different from that of the control group.This could be due to the fact that the metaflumizone strain used in the study was sensitive and had a weak detoxification ability.The findings revealed that the combination of DEM and PBO had a synergistic effect on indoxacarb toxicity,with synergistic multiples greater than 1.5 times.However,the synergistic multiples of TPP and DEM to spinetoram were lower than 1.3 times,while the synergistic multiples of PBO to spinetoram were 1.78 times.The results indicate that the detoxification metabolism of FAW to indoxacarb is associated with increased activity of GST and MFO,while the detoxification metabolism to spinetoram is related to increased activity of MFO.3.Effects of sublethal doses of metaflumizone and indoxacarb on the activities of three detoxification metabolizing enzymes in S.frugiperdaThe objective of this study was to examine the impact of metaflumizone and indoxacarb at sublethal concentrations(LC₁₀ and LC₃₀)on three detoxification metabolizing enzymes,namely Car E,GST,and MFO.Third instar larvae of FAW were treated with the chemicals and enzyme-linked immunosorbent assay was conducted at 12,24,48,and 72 hours after treatment to determine changes in enzyme activity.The study found that after treatment with a sublethal concentration of metaflumizone,the activity of MFO was initially induced and then inhibited,while the activity of GST was induced.The change in Car E activity was not significantly different from the control group within 72 hours.Similarly,sublethal indoxacarb treatment enhanced the activities of MFO and GST within 72 hours,but there was no significant difference in Car E activity compared to the control group.There is speculation that GST could has a significant impact on the detoxification metabolism of metaflumizone,MFO and GST may play an important role in the detoxification metabolism of indocarb by FAW.