| As a worldwide pest mite,the carmine spider mite(Tetranychus cinnabarinus)is a wordwilde pest,causing serious loss to a variety of agricultural crops,thus,the control of T.cinnabarinus is of great importance to economy and ecology.At present,application of chemical pesticides is the main approach to control T.cinnabarinus in the filed.But owing to frequent use of acaricides,carmine spider mites can easily develop resistant to various pesticides,which lead to pest resurgence.It has been reported that sublethal doses of pyrethroids stimulate the fecundity of some pests.We also found that laboratory selected resistant strain of T.cinnabarinus(FeR)of the same origin has a stronger fertility than the susceptible strain(SS).Therefore,this study intended to investigate the underlying molecular mechanisms related to enhanced fecundity in FeR,which clarify the mechanism of resurgence caused by pyrethroids.Previous study confirmed that the protein and gene levels of vitellogenin(vg)and vitellogenin receptor(vgr)in FeR strains were higher than those in SS strains.As process of vitellogenesis is regulated by juvenile hormones or ecdysone in pest.We focused our research on the hormonal regulation mechanism.The content and results are as follows:1.Effect of fenpropathrin and hybridization on fecundity of T.cinnabarinus.SS and FeR were treated by sublethal dose of fenpropathrin,and it was found that the oviposition amount of both strains significantly decreased,indicating that sublethal dose of fenpropathrin did not stimulate the proliferation of both lines of T.cinnabarinus.2.The presence of MF(methyl farneyl ester)in T.cinnabarinus was identified by GC-MS,but JH III was not detected.There was no significant difference in MF titer of 5-day-old adult mites between two strains,indicating that juvenile hormone is not the main factor related to fertility.The total content of ecdysone in T.cinnabarinus was determined by Ecdysone enzyme-linked immunosorbent assay kit.It was found that the content of ecdysone at 5-day-old stage(5A)in both lines was higher than that at 1-day-old stage(1A)and 10-day-old stage(10A),which was consistent with the trend of daily average egg production,Furthermore,the total amount of ecdysone in the FeR was significantly higher than that in SS strain at 1A and 5A,and it was found at 10 A,indicating that ecdysone may be a contributing factor to the enhanced fertility of FeR.3.By analyzing the transcriptome data of T.cinnabarinus,we screened out the genes in ecdysone synthesis pathway and ecdysone receptor gene,which were: TcNvd(Rieske domain protein),TcSro(non-glossy/shroud),CYP307A1(spook),CYP302A1(disembodied),CYP315A1(shadow),CYP314A1(shade),EcR.The relative expression of these 7 genes in the 5-day-old adult of the two strains was detected.Four genes(TcSro,CYP315A1,CYP314A1,EcR)were up-regulated in FeR and RNAi was performed on CYP314A1 and EcR,respectively.When the expression of EcR was silenced,the relative expression of Tcvg1 significantly decreased by 61.26%,and the oviposition amount of T.cinnabarinus also significantly decreased by 35.93%.After CYP314A1 was silenced,the relative expression of Tcvg decreased by 57.73%,and the content of ecdysone decreased by 36.59%.The total number of eggs was significantly reduced by 34.48%.It indicated that CYP314A1 and EcR were involved in the spawning process of FeR strains,and ecdysone could regulate the oviposition behavior of T.cinnabarinus.The results suggested that exposure to sublethal does of fenpropanthrin could not stimulate the fecundity of T.cinnabarinus.Enhanced fecundity in FeR strains is a concomitant phenomenon of fenpropathrin resistance.The process of vitellogenesis of T.cinnabarinus is regulated by ecdysone.Compared with SS strain,the expression of ecdysone synthesis pathway genes TcSro,CYP315A1 and CYP314A1 were up-regulated in FeR,which resulted in the increase of ecdysone content,and expression of the nuclear receptor EcR was significantly up-regulated in FeR.So this lead to a corresponding increase in the content of vitellogenin,finally,which resulted in a significant increase in fertility.This mechanism may be the direct reason for the enhanced fertility of FeR. |
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