| Spodoptera litura mainly harms crops such as beans,cottons and vegetables.It is one of the main pests of crops and causes great economic losses to agricultural production in China.However,the resistance of pests to insecticides is increasing,which leads to increasing use of insecticides,environmental pollution and secondary disasters.Therefore,it is of great significance to find new insecticides to prevent and control pests and delay their resistance.Fluralaner is a new kind of insecticide with excellent insecticidal activity against Lepidoptera insects.However,its activity and sublethal effect on S.litura are still unclear.Therefore,the effects of fluralaner on the lethal and sublethal activities of S.litura were determined.The aim of study is to provide scientific basis for the application of fluralaner in the control of S.litura.1 Effects of fluralaner on insecticidal activity and growth and development of S.lituraTo investigate the insecticidal activity of fluralaner against S.litura,in this study,the toxicity of S.litura at different ages and the synergistic effect of synergists were determined by topical application and feeding application.The results showed that LD50 of fluralaner on 3rd instar larvae decreased from 6.14 ng/larva at 24 h to 3.24 ng/larva at 96 h and the 5th instar larvae decreased from 471.58 ng/larva at 24 h to 202.04 ng/larva at 96 h after topical application.The LD50 of fluralaner on 1st instar larvae decreased from 0.53 mg/kg at 24 h to less 0.0625 mg/kg at 96 h,3rd instar larvae decreased from 0.84 mg/kg at 24 h to 0.15 mg/kg at 96 h,5th instar larvae decreased from 1.15 mg/kg at 24 h to less 0.125 mg/kg at 96 h.The LC50 of adults at 24 h and 48 h were 38.97 mg/L and 4.29 mg/L,respectively.It was found that the sensitivity of S.litura to fluralaner decreased with the increase of age.The hatching rate of eggs was strongly decreased from 92.2 ± 4.84%of control to 45.56 ± 4.01%of 2 mg/L fluralaner.The results showed that the hatching rate decreased with the increase of the concentration of fluralaner.The synergistic effects of different synergists on fluralaner were different.The synergistic ratios of TPP,PBO and DEM for 3rd instar larvae were 1.55,1.21 and 0.92,respectively.The synergistic ratios for 5th instar larvae were 1.99,1.18 and 1.08,respectively.After feeding application,the synergistic ratios of PBO,DEM and TPP to 3rd instar larvae were 1.74,1.23 and 1.17,respectively.The data show that PBO has the strongest synergistic effect on fluralaner.In order to clarify the reasons for the above effects,the gene expression profiles of detoxification enzymes such as GSTs and P450s were analyzed.The relative expressions of SlCYP4M14,SlCYP6B47,5lCYP6B48 and SlCYP6B58 were significantly increased 1.56-6.45 times at 72 h after fluralaner treatment.The relative expression of SlGSTel,SlGSTs4 and SlGSTs5 respectively increased 5.6,4.3 and 20.4 times at 96 h.Therefore,P450 may be involved in the metabolism of fluralaner,which is consistent with the results of PBO synergistic experiment.In this study,LD15(0.54 mg/kg)were used to treat the larvae,and the effect of sublethal dose of fluralaner on the growth and development of S.litura were determined.The results showed that the average duration of larvae was prolonged 0.9 days at treatment.The average pupa duration of pupation was significantly prolonged 0.7 days at treatment.The pupa weight significantly decreased 16-30 mg/pupa.The adult life span was significantly shortened 0.8 days.This indicated that the sublethal dose of fluralaner had a significant effect on the growth and development of S.litura.In this study,the gene expression profiles of five developmentally related genes CHS,CHT5,Jhamt,JH-SRC and Toros-like were analyzed.The results showed that the expression of SlCHS decreased significantly to 60%at 48 h.The relative expression of SlCHT5 increased significantly to 2.3 times at 24 h,SlJhamt increased significantly 1.7-3.3 times at 24 h to 96 h,SlJH-SRC increased significantly 1.3 times at 24 h,SlTorso-like had the highest expression at 48 h and decreased at 96 h,which was 40%control group.These results suggest that fluralaner may affect the growth and development of S.litura by interfering with the expression of growth-related genes.2 Sublethal effects of fluralaner on GABA auxiliary proteins(nlg and LH4).The effects of insecticides on target receptors have been studied extensively,but the interference of target receptor auxiliary proteins are rare.Therefore,the gene expression of ionotropic GABA receptor auxiliary proteins(nlg and LH)were detected in S.litura in this study.Five Slnlg and one SlLH4 gene sequences of S.litura were obtained from NCBI database,and primers were designed according to the gene sequences.The amino acid sequence of nlg gene of S.litura was compared with that of other insects.From the phylogenetic tree,it was found that the nlg and LH4 of S.litura were clustered into one group with other insects,which indicated that the nlg and LH4 of these insects had close relationship.Gene expression profiles of different stages and tissues showed that the highest expression of Slnlg1、Slnlg2、Slnlg4-yl1、Slnlg5 genes were found in egg,larval stage and epidermis.The highest expression of Slnlg3 gene was found in adult stage and malpighian tube，they were 3.3 times as 6th instar larvae and 22.8 times as head.The highest expression of SILH4 was found in adult stage and head,they were 2.2 times as 3rd instar larvae and 9.3 times as fat body.After the treatment of Slnlg3 and SlLH4 genes with dsRNA,the expression of Slnlg3 gene was significantly inhibited at 6 h and SILH4 gene was significantly inhibited at 6 h and 12 h.The phenotypic changes and mortality of S.litura of interference with nlg and LH4 genes by dsRNA(dsnlg3 and dsLH4)after 96 h were observed.The average mortality was 3.33%in dsEGFP injection group,6.67%-13.33%in dsnlg injection group and 13.33%in dsLH4 injection group.There was no significant difference between the two groups.3rd instar larvae of S.litura were treated with LD15 fluralaner for 24 h.The expression of Slnlgl and Slnlg2 was significantly higher than control,while the expression of Slnlg3 and Slnlg4-yll remained unchanged,and the expression of Slnlg5 gene was significantly down-regulated.The expression of SlLH4 was L5 times higher than control group,but there was no significant difference.These results suggest that the gene expression profiles of Slnlg and SLH4 were significantly affected by fluralaner. |
PDF Full Text Request