Characteristics And Ecological Adaptability Of Cuticular Lipid In Locusta Migratoria

Cuticular lipids are located in the epicuticle of the integument.The main component is hydrocarbons.It has multiple functions such as water retention,desiccation resistance,pheromone,and prevent pathogen infection.It is the first barrier of the insect,which protect the insect body from external environmental pressure,and plays a vital protective role in the process of insect life metamorphosis.The composition,structure,content and distribution of the cuticular lipids are the main factors that determine whether they can survival in severe adversity.In this thesis,Locusta migratoria,an agricultural pest that mainly damages gramineous plants and has devastating damage was selected as the research object.The characteristics of cuticular lipids,the regional distribution characteristics of the cuticular lipids on different tissues of the L.migratoria,and its relationship with ecological adaptability were studied in this thesis,in order to provide a basic basis for the control of locusts.The main results are shown as follows:1.Analysis of cuticular lipids characteristics of L.migratoriaIn this chapter,eosin dying experiment was used to observe how eosin penetrates the cuticle of locusts at different temperatures;water-soluble dyes of different molecular weights,including toluidine blue,methylene blue,eosin,erythrosine and basic fuchsin,were selected to dying the L.migratoria,in order to observe the coloring of the cuticle,and further study the influence of external factors on the cuticular permeability of locusts cuticle.The results showed that,the color of the integument of the insect gradually darkened and the dye infiltrated into the body gradually increased with the temperature increased;the cuticle of the L.migratoria can be slightly colored,but the insect body is not colored at 45℃;while from 55℃,the surface and the inside of the insect body can be seen clearly red;at 65℃,the internal of the L.migratoria can be clearly observed red coloring.At a constant temperature of 45℃,among the red dyes,erythrosine has the strongest permeability,followed by basic fuchsin and eosin the weakest.Among blue dyes,the permeability of toluidine blue is stronger than that of methyl blue.No correlation between molecular weight and dye permeability is found according to the comparison of molecular weight.The above results showed that the difference in temperature and dye is one of the factors that affect the cuticular permeability.According to the difference in the elution efficiency of cuticular lipids by different organic solvents,five organic solvents,including chloroform,ethyl acetate,n-heptane,acetone,and n-hexane,were selected to elute the insects.After eosin staining,it was observed that the insect body after chloroform elution is the easiest to dying,and the inside and outside of the insect body is full of eosin dye;and followed by ethyl acetate and n-heptane.After elution with n-hexane,the thorax of the insect is colored,while the coloration is not obvious after acetone is eluted.The results showed that changes of the cuticular lipids of the L.migratoria caused by the elution of organic solvents affect the permeability of the cuticle of the L.migratoria.2.Regionalized distribution of cuticular lipids in L.migratoriaDifferent temperatures have different coloration on different parts of the cuticle of the L.migratoria.The lipid content of the cuticle is related to the cuticular permeability.The structure and distribution of lipids on the insect cuticle affect its adaptability in the living environment.This chapter uses nhexane to extract cuticular lipids in different tissues,including head,antennae,feet,wing buds and abdominal cuticle of the locust,and analyzes them by gas chromatography-mass spectrometry(GC-MS).The results show that there is no difference in the cuticular hydrocarbons on male and female nymphs.Obviously,female nymphs cuticular linear alkanes C27 and methyl branched alkanes 3-Me C27 are higher than male nymphs,and the content of other components is almost equal;but the cuticular hydrocarbons of different tissues of locusts are different.The content of cuticular hydrocarbons of the appendages(tentacles,feet and wings)of L.migratoria is significantly higher than that of the head,thorax and abdomen of the insect body.This difference is related to the permeability of the cuticle.3.Influence of cuticular lipids of L.migratoria on ecological adaptabilityBased on the previous research of our research group on the key gene functions of the cuticular lipids synthesis of the L.migratoria,the fatty acid synthase genes Lm FAS1 and Lm FAS3,and the fatty acyl-Co A reductase gene Lm FAR13,which affect the cuticular lipids biosynthesis pathway of the L.migratoria,were selected and silenced by RNA interference.The ecological adaptability of locusts under desiccation and insecticides,was analyzed.The results showed that the water-retaining ability of L.migratoria cuticle and insecticide resistance were reduced to varying degrees after RNAi,indicating that the content of cuticular lipids can affect the ecological adaptability of locusts.The study in this thesis showed that the cuticular permeability of L.migratoria gradually increases with the increase of the temperature,which may be caused by the lipid phase transition and the corresponding changes in arrangement;the permeability of different dyes to the cuticle is different;the organic solvents have different effects on the dissolve the cuticular lipids,which caused differences in the cuticular permeability of the L.migratoria;the regionalized distribution of cuticular lipids of the L.migratoria is consistent with the cuticular permeability;the silencing of key genes in the cuticular lipid synthesis of the L.migratoria reduced the ecological adaptability of the L.migratoria.This study provides a basis for pest control based on cuticular lipids.