Effects Of Bistrifluron On The Fecundity And Expression Of Vitellogenin And Its Receptor In Spodoptera Litura

Spodoptera litura?Fabricius?is one of the main vegetable pests,which is apolyphagous pest insect distributed in worldwide.Due to the excessive reliance on the chemical control and and its rapid reproduction,S.litura has developed serious resistance on some traditional chemical insecticides.Bistrifluron is an efficient insect growth regulator and inhibits the insect chitin synthesis,which can be degraded rapidly in the environment.The resistance levels of 6 kinds of chemical insecticides to five field-collected populations of S.litura in Sichuan Province was determined.Based on the toxicity of tested insecticide to S.litura,the sensitive andresistant homologous strains were obtained through two-direction screening using DY population with the highest resistance to bistrifluron as parent.The differences of growth and development,reproduction,reproduction between sensitive andresistant-bistrifluron strains?Bis-UNSEL and Bis-SEL strains?were further determined.The expressions of vitellogenin?Vg?and its receptor?VgR?in pupa and female adults of Bis-UNSEL and Bis-SEL strains were analyzed by qRT-PCR,and the expressions of Vg and VgR genes in Bis-UNSEL and Bis-SEL strains were analyzed by transcriptome sequencing.The key genes influencing the fecundity of S.litura were analyzed and elucidated that the molecular mechanism of the Vg and VgR genes expressions and the fecundity difference during developing the resistance of S.litura to bistrifluron.The detail resultsare summarized as follows:The toxicities ofbata-cypermethrin,chlorpyrifos,methyl abamectin benzoate,methoxylhydrazide,chlorpyrifos,and bistrifluronon a susceptible strains?Lab-HN strain?of S.litura and five field populations?MS,LS,PZ,DY and YB?were assayed by stomachpoison method.The results showed that all populations had high resistance level to bata-cypermethrin?with resistance ratios?RR?of 5574.3-to 9003.7-fold?and chlorpyrifos?185.0-to 941.4-fold RRs?,and medium resistance level to methyl abamectin benzoate?12.5-to 40.0-fold RRs?,to methoxylhydrazide?28.2-to 36.1-fold RRs?,to chlorpyrifos?12.0-to 21.5-fold RRs?,and to bistrifluron?15.9-to 77.7-fold RRs?,respectively.The DY population with the highest resistance to bistrifluron?77.7-fold RRs?was used as parents to develop the Bis-UNSEL and Bis-UNSEL strains by the two-direction screening.After screening successively six generations,the Bis-UNSEL strain was sensitive to distrifluron compared with the Lab-HN strain,while the Bis-SEL strain increased to 113.8folds RRs.The growth and developmental parameters of Bis-UNSEL and Bis-SEL strains at each age stage were recorded and analyzed by the theory of tow-sex life table.The results indicated that the total preoviposition?TPOP?of Bis-SEL strain was significantly shorter than that of Bis-UNSEL strain,while the fecundity of Bis-SEL strain was higher than that of Bis-UNSEL strain.The intrinsic rate ofincreate?r?,finite rate of increase???and the net reproductive rate?R₀?of Bis-SEL strain were significantly promoted,while the total reproduction rate?GRR?and the mean generation time?T?were significantly shortened.The differences of reproductive indexes between Bis-UNSEL and Bis-SEL strains were further analyzed and found that pre-spawning period and oviposition duration of Bis-SEL strain were longer than that of Bis-UNSEL strain.The change trends of theresidual eggsnumber,production rate,hatching rate of larvae,weight of adult female,ratio of Bis-UNSEL testis and ovarian tube index of Bis-SEL strains were the same even through the difference was not significant.The proportion of ovary,life span and potential oviposition of adult female in Bis-UNSEL strain were lower than those in Bis-SEL strain.The expression of Vg and VgR genes in Bis-UNSEL and Bis-SEL strains were found to start in the stage of pupal stage using qRT-PCR analysis,and the expression level increased firstly and then decreased with the development of female adult ovary,and reached its peak at 36 h after emergence.Meanwhile,the relative expression quality of Vg gene in Bis-UNSEL strain was significantly higher than that in Bis-SEL strain,on the contrary,the expression level of VgR gene in two strains was opposite.The changes of Vg and VgR proteincontents in Bis-UNSEL and Bis-SEL strains were consistent with their gene expressions,and the protein content of Vg and VgR in Bis-UNSEL strain was lower than that in Bis-SEL strain.The differential expressed genes?DEGs?between Bis-UNSEL and Bis-SEL strains were analyzed by transcriptome sequencing analysis,and each strain was repeated three times.There was 46.61Gb Clean Dataand 633 new genes in total were discovered.There were20 DEGs,including 13 up-regulated genes and 7 down-regulated genes.Differential gene molecular functions are annotated into three categories:biological process,cellular component and molecular function.Cluster analysis showed that the expression of DEGs in Bis-UNSEL and Bis-SEL strains showed a high correlationexcept for gene1466 and gene3097 genes in Bis-UNSEL strain newgene3304 and newgene5403 in Bis-SEL strain.KEGG analysis showed that the DEGs were mainly mapped to lipid metabolism pathway.According to the classification of WGCNA functional modules,it was found that VgR gene was enriched in blue module.The main functions included:cellular processes,environmental information processing,genetic information processing and metabolism.Meanwhile,some detoxifying enzymes are also enriched in it.