Study On The Mechanisms Of Juvenile Hormone Regulating Ogenesis And Vitellogenesis In Propylea Japonica

Propylea japonica is an important predatory natural enemy in agricultural ecosystem.However,in the current artificial breeding process of P.japonica,no artificial diet has been found to completely replace the natural prey.The artificial diet leads to a significant decline in its reproductive capacity and even a failure in completing the generation well.However,the reason of this reproductive decline is not clear,and the molecular mechanism of reproductive in P.japonica is rarely studied to date.Clarifying the molecular mechanism of P.japonica reproduction are helpful to find the key regulatory factors for better artificial breeding of ladybirds.In this study,the developmental duration,fecundity,body length and width were investigated;the JH titers in different developmental stages of P.Japonica were measured;the morphological changes of ovaries and follicular epithelial cells of P.japonica were observed systematically.We choose the different development stages of P.japonica females for transcriptome sequencing and the time series expression profiles analysis,and a large number of differentially expressed gens（DEGs）related to reproduction at different developmental stages were identified.Finally,RNAi technology was used to explore the role of juvenile hormone and its receptor gene Met in reproductive regulation of P.japonica.The conclusions are as follow:1.The average duration of the 1^st,2^nd,3^rd,4^th instar larvae,pupal,female adults and male adults of P.japonica was 1.13 d,1.48 d,1.34 d,2.34 d,2.81 d,51.08 d and 48.36 d,respectively.Besides,the highest number of eggs produced per female per day was 14.42.The average number of eggs laid by a single female was 414.The maximum number of eggs laid by a single female was 654.The body length of P.japonica increases rapidly from 2^nd to 3^rd instars in larval stages.The larva reaches the longest body length of 9.32 mm at the 4^th instar stage,and the body width reaches the widest 3.70 mm in the adulthood.2.During the period of P2(2^ndday after pupation)and P3(3^rdday after pupation),two fully developed ovaries can be clearly observed.Besides,ovarioles in this period were surrounded by many microtubules.From P3 to D1 stage(1^stday after eclosion),the shape of the ovarioles was thin and short fusiform.From D1 to D2(2^nd day after eclosion)stage,the ovarioles gradually dilates and differentiates to form the egg chambers.From D2 to D3(3^rd day after eclosion)stage,one or two oocytes in different developmental stages can be observed,and the uptake of yolk proteins by the primary oocytes began.From D3 to D4(4^th day after eclosion)stage,the color of primary oocytes gradually darkens（changing from milky white to light yellow）,the oocytes deposit a large amount of vitellogenin,and even a few oocytes nearly matured.From D4 to D5(5^th day after eclosion)stage,the primary oocytes changed from light yellow to bright yellow,and a large number of oocytes were matured.3.From the 1^st day to the 3^rdday after adult emergence,the distance between nuclei of the follicular epithelia increased from 1.94μm to 4.57μm,the diameter of nuclei increased from 8.50μm to 11.06μm,the cells were closely arranged,and all nuclei occupied almost full of the whole cell.During this period,the cells gradually expanded,but patency between the follicular epithelial cells cannot be observed.During the development of female adult from the 3^rd day to the 5^th day,the nucleus spacing increased sharply from 4.57μm to 16.4μm,and the nucleus diameter also increased from 11.06μm to 15.76μm.The cells became round and patency could be clearly observed.4.The titer of JH III increased approximately two folds rapidly and reached the peak（1.14 ng/mg）in 2^ndinstar,and then decreased gradually to the lowest level（0.17 ng/mg）in the pupal stage.After eclosion,JH III titer rose again and peaked（1.08 ng/mg）in 2 days old female adulthood,then reduced drastically except a short and slight increase in the 4 days old adult stage.Transcriptome analysis indicated that a lot of JH synthesis and metabolism-related enzyme genes and some potential nutrient signal sensing and transduction related genes were significantly differentially expressed in the course of P.japonica reproductive development.We selected the JH receptor gene Met to investigate the effects of JH deprivation on the reproduction.Actually,the oogenesis,vitellogenesis and follicular epithelium development in the ds Met treatment group was significantly inhibited.In this study,the developmental duration,daily oviposition quantity,body length and body width of P.japonica were investigated.The development of the ovaries,the change dynamics of juvenile hormone titer and the development of follicular epithelial cells of P.japonica were determined.Dynamic transcriptome analysis and Methoprene-tolerant gene knockdown reveal that juvenile hormone regulates oogenesis and vitellogenin synthesis in P.japonica.