Research On Regulation Mechanism Of Juvenile Hormone On Reproduction And Diapause In Neoseiulus Barkeri

With the promotion of green prevention and control,natural enemy products have attracted a lot of attention,and predatory mites have been widely used as the dominant species of natural enemy to control small juice sucking pests and mites in the field.As a member of predatory mites,Neoseiulus barkeri is considered to be one of the dominant species of predatory mites due to its wide feeding capacity,strong predatory ability,strong reproductive ability and good diffusivity.However,it has been found in practical application that the mortality rate after long distance transportation is very high.Therefore,in order to solve this problem,the laboratory has bred the diapause strain of N.barkei with appropriate combination of light and temperature,so as to prolong the life and stress resistance,achieve the purpose of extending the shelf life and reducing the mortality rate during long distance transportation.How to quickly break the diapause and enhance the reproductive capacity of the diapause strains of N.barkeri has become a new issue to be solved in practical applications.Therefore,this article uses quantitative fluorescence and RNAi technology to explore the role of juvenile hormone and its receptor in the reproduction and diapause of N.barkeri.This work laid a foundation for further research on hormone-dependent switch from diapause to reproduction in N.barkeri.Below are our key research findings:1.Through bioinformatics analysis of the Met gene of N.barkeri,we found that it has the highest amino acid sequences similarity with those of Galendromus occidentalis.The open reading frame of NbMet is 1332 bp,encoding 466 amino acids The predicted relative molecular weight is 52619.50Da The theoretical isoelectric point is 6.90.The fat coefficient is 73.45 and the total average hydrophilicity(GRAVY)is-0.469.It is a hydrophilic protein,with neither signal peptide nor transmembrane region.The protein is mainly composed of α helix and random coil winding folds.Compared with the Met sequences of other species,NbMet shows characteristics of the b HLH-PAS(helix-loop-helix-Per-ARNT-Sim)transcription factor family.Analysis of the expression patterns of NbMet in different developmental stages and diapause adult female mites found that the expression abundance of NbMet was higher in the stages of larva and protonymph,and lowest during the diapause period of adult female mites.This suggests that NbMet may be involved in the regulation of reproductive diapause of N.barkeri.2.We found that JH plays an important role in the reproduction and diapause release of N.barkeri.After the first emergence of diapause,female adult of N.barkeri were treated with juvenile hormone analog(JHA)solution at a concentration of 75μg/mL.Accordingly,oviposition was observed on the 10 th day after ovary development.And the triglyceride abundance in the female adult was decreased on the 5th day.The expression of NbFas was downregulated,NbVg and NbVg R were upregulated.These results show that,in N.barkeri,JH can promote the development of the ovary of through increasing the transcription level of NbVg and NbVg R,andinhibit lipid synthesis through declining the expression of NbFas.Moreover,exogenous JH can induce Met transcription.3.To explore how NbVg,NbVg R and NbFas are regulated,we used RNAi technology to silence the Met in the first emerging non-diapause female adult of N.barkeri.Remarkably,5d after the knockdown experiment,ovarian development was delayed,reproductive capacity was reduced,life span was extended,the triglyceride content rose,NbVg and NbVg R expression levels were down-regulated,NbFas expression was up-regulated.This might indicate that Met is involved in the regulation of reproduction and diapause of N.barkeri.After being interfered with Met,the diapause female adults of N.barkeri were treated with JHA.As expected,compared with the control group,NbMet transcript cannot be enhanced by JH,both NbVg and NbVg R could no longerexpressed normally,the expression of NbFas was up-regulated.The results show that in the case of Met silencing,JH cannot play the function of promoting reproduction and eliminating diapause.Taken together,Met is proved to be a key receptor in the JH signaling pathway of N.barkeri.Our results demonstrate that JH increases the expression of NbVg and NbVg R through Met,in order to promote the reproduction and inhibit the occurrence of diapause of N.barkeri.JH-Met can also suppress the expression of NbFas,inhibit the formation of lipids,so as to inhibit the occurrence of diapause.