| Scale insects(Insecta,Hemiptera,Sternorrhyncha,Coccoidea)are recorded more than 8,300 species worldwide,most of which are main pests of forestry,agriculture,fruit trees and flowers.Scale insects are divided into two groups: Archaeococcoids and Neococcoids.There are a variety of wax glands on their body walls to secrete wax and form wax shells,which make difficult for chemicals to penetrate,and increase the difficulty of prevention and control.Ziziphus jujuba is one of the main host plants of scale insects.Its fruit called as Jujubi has high nutritional value,and is rich in many vitamins,iron and calcium.Jujubi has the functions of detoxification and beauty,soothing liver and relieving depression.It can also improve sleep quality,soothe the nerves and invigorate the brain.Drosicha corpulenta and Ceroplastes japonicus,belonging to Archaeococcoids and Neococcoids,respectively,are the main pest groups that damage Ziziphus jujuba Mill.They are distributed in the jujube planting areas of Shanxi Province,especially in the southern part of Shanxi.Outbreaks of scale insects will seriously affect their growth and reduce yield.Specie genetic variation and taxonomic status are very important for understanding its occurrence and formulating appropriate control methods.Mitochondrial DNA sequences as good markers are increasingly used in this area of research.At present,there are few studies on the mitochondrial genome of scale insects.Based on the next-generation high-throughput sequencing technology,we sequenced the genome of C.japonicus and D.corpulenta,and assembled their complete sequences of the mitochondrial genome,and analyze their length,base composition and genetic composition.Comparing with scale insect sequences published in GenBank,we analyzed sequence composition and structural variation,and further explore the variation of scale insect mitochondrial genome.We also Compared and analyzed the insect sequences of Sternorrhyncha published in GenBank,and constructed the phylogenetic relationship of Sternorrhyncha to analyze their calssification position.The main research results obtained are as followings:1.We obtained the complete sequence of the mitochondrial genome of C.japonicus.It is 15,091 bp in length and contains 33 genes: 9 protein coding genes(PCGs),22 tRNAs and 2 rRNAs.The AT content of the mitochondrial genome is85.3%,which has obvious AT preference.The 9 PCGs are: COI,COII,COIII,Cytb,ND1,ND3,ND4,ND5 and ATP6 genes.All PCGs use ATN as the start codon,and TAA is the stop codon except for COII which is terminated by a single T.Twenty-two tRNAs are between 44 bp-69 bp in length,8 tRNA genes are located on the light chain,and the others are located on the heavy chain.Among them,tRNA-Ser1,tRNA-Asn lack D loop and D stem,tRNA-Cys,tRNA-Trp lack D loop,tRNA-Glu,tRNA-Phe and Trp lack TΨC loop and TΨC stem,tRNA-Val lack TΨC loop,tRNA-Gly,tRNA-Pro and tRNA-Ser1 lack the TΨC stem,and the rest of the tRNA can form a clover structure.2.We obtained the incomplete sequence of the mitochondrial genome of D.corpulenta with the length 14,082 bp,containing 22genes: 8 PCGs and 14 tRNAs.The AT content of mitochondrial genome is 84.7%,which has obvious AT preference.The 8 PCGs are: COI,COII,COIII,Cytb,ND3,ND4,ND5 and ATP6 genes.All PCGs use ATN as the start codon and TAA as the stop codon except for COIII terminating with a single T and ND5 with TAG.The 14 tRNAs are between 46 bp-67 bp in length,among which 4 tRNA genes are located on the light chain,and the others are located on the heavy chain.Oonly 6 tRNAs can form a clover structure,whereas,the tRNA-Asn and tRNA-Arg lack D loop and D stem,tRNA-Glu,tRNA-Phe,tRNA-Gly,tRNA-Pro,tRNA-Arg,tRNA-Thr and tRNA-Trp lack TΨC loop,tRNA-Asp lacks the TΨC stem.3.We downloaded the mitochondrial genomes of C.japonicus,Saissetia coffeae,Ceroplastes rubens,Planococcus citri and Unaspis yanonensis from GenBank and re-annotated to perform the analysis of comparative genomes and BLASTn.The results showed that the number of protein-coding genes were between 8-13,and the number of tRNAs was 14-22.All protein-coding genes use ATN as the start codon except the COII genes of C.japonicus and S.coffeae using a single T.The stop codons are TAA or TAG except for the COIII gene of D.corpulenta using a single T.4.We downloaded the mitochondrial genome sequence of Sternorrhyncha from GenBank,and compared and analyzed its sequence composition.The size of the mitochondrial genome of Sternorrhyncha is between 14,496 bp-18,414 bp,and most of the species are between 15.0 kb-17.0 kb in length and consist of 33-41 genes.The gene order of the mitochondrial genome of Psylloidea is very conservative and the same as Drosophila melanogaster.In Coccoidea,gene rearrangement occurred between ND6-trn W,the other genes changed positions except the conservative Cytb-CR region.In Aphidoidea,the main feature of the mitochondrial genome was the existence of repetitive regions between tRNA-Glu-tRNA-Phe and tRNA-S1-tRNA-Glu,and some species exchanged positions of tRNA-Gln and tRNA-Met.In Aleyrodidae,the sequence of gene arrangement is relatively diverse.Most species involve the inversion of the ND3-tRNA-Gly-COIII gene,and some tRNAs have different frequency of gene rearrangements.5.We used 82 species of Sternorrhyncha with Aphaena discolor nigrotibiata as the outgroup to construct ML phylogentic tree based on 8 protein coding genes.The phylogenetic analysis supported the monophyly of the four superfamilies with 100%support value,and the relationships of the four superfamilies in the suborder Sternorrhyncha are:(((Coccoidea+Aphidoidea)+Aleyrodoidea)+Psylloidea).In summary,scale insects are a special group in the Sternorrhyncha,and there are great variations in the mitochondrial genome of scale insects,which need to be further studied. |
