Studies On The Wax Compositions And Its Biosynthesis Related Gene Far In Cotton Mealybug,Phenacoccus Solenopsis Tinsley(Hemiptera:Pseudococcidae)

The cotton mealybug,Phenacoccus solenopsis Tinsley(Hemiptera:Pseudococcidae),is an alien invasive pest that is expanding in China and posing a threat to agricultural production of the country.The body surface of this mealybug is covered with wax powder which putatively has important functions,in particular protecting themselves.However,its compositions,synthesis related genes and their its expressional patterns as well as biological functions remain unknown.In this study,we observed the category and structure of wax glands,identified the chemical compositions of wax secretions,and determined the expression level of wax synthesis related genes fars in different developmental stages of the cotton mealybug.Several far genes were also interference by RNAi.The results are as follows:1.Three kinds of waxy glands were observed on the body surface of P.solenopsis,dominated by trilocular pores,followed by tubular glands and multilocular disc pores.According to the results of GC-MS,wax secretions were mainly composed of hydrocarbons,alcohols,fatty acids,ketones,aldehydes and esters,as well as derivatives that contain aromatic groups.2.Four fatty acyl-CoA reductases(FAR,found to be involved in wax biosynthesis in other organisms)show gene expansion,named as Psfar-1,Psfar-2,Psfar-3,and Psfar-4.Analysis on amino acid sequences showed that they possessed a rossmann folding domain at their N-terminal which contained both NAD(P)H binding motif TGXXGXXG and FAR active site motif YXXXK.Among them,Psfar-1,Psfar-2 and Psfar-3 were highly in the pupa stage;and relatively lower in nymphal stages,while Psfar-4 was highly expressed in nymphal stages and adult females,but lowly in the pupa stage.All these four genes were lowly expressed in adult males.3.After microinjection of dsRNA into 3rd-instar nymphs,the expression levels of Psfar-1 and Psfar-2 were significantly decreased,however,wax on the body surface of injected nymphs did not reduce significantly.In short,this study clarified the types of wax glands and the chemical constituents of wax secretions in P.solenopsis,and clarified the expression levels of four far genes at different developmental stages.The results are expected to be informative for further studyies wax biosynthesis processes and its biological functions.