Molecular Identification And Phylogenetic Studies Of Coccidae

The family Coccidae(Hemiptera:Coccoidea)is the third largest family of scale insects,which is a pest that seriously endangers many kinds of cash crops in China.Rapid and accurate identification is the basis of monitoring and effective prevention and control,but there are many difficulties and deficiencies in traditional morphological identification methods.A total of 367 DNA barcode data were extracted from 44 species,belonging to 19 genera of Coccidae by used DNA barcode technology.We acquired 151 sequences of COI genes,116 sequences of 28 S genes and 100 sequences of 18 S genes,expanded the number of sequences and species in the Gen Bank database,and improved the identification ability of the database.Based on the barcode data of other Coccidae insects in Gen Bank,it can be concluded that: COI gene had the highest degree of variation,with an average mutation site accounting for 90.2%,A+T content was 78.1%,C+G content was 21.9%,and the base composition had obvious A+T bias.The ratio of transformation to transversion was 0.9,which was higher than the critical value of 0.4.Transformation and transversion mainly occur at the third codon;The average mutation site of 28 S gene was 90.1%,A+T content was 36.5%,less than 63.5% of C+G content.The base composition had C+G bias,and the ratio of transformation to transversion was 1.0(>0.4);18S gene was the most conserved,with a mean ectopic point of 40.0%,an average A+T content of 47.2% and a C+G content of 52.8%.there was no obvious base bias,and the ratio of conversion to turnover was 1.3(>0.4).The genetic distance between the COI genes was the largest,ranging from 0.19% to 48.88%,with an average inter-species genetic distance of 23.00%;the genetic distance between 28 S sequence genes ranged from 0.00% to 41.43%,but the minimum genetic distance between 12 species was 0,with an average inter-species genetic distance of 13.00%;the genetic distance between 18 S genes was the smallest,ranging from 0.00% to 24.61%,and the minimum genetic distance between 20 species was 0,with an average inter-species genetic distance of 6.00%.According to the results of phylogenetic analysis,Coccidae can be divided into three parts: A-group,B-group and Toumeyalla-group.A-group includes: Paralecaniini,Megapulvinaria,Filippiinae,Cardiococcinae and Eulecaniinae.B-group can be broadly divided into two smaller branches: The first is Ceroplastinae;The second includes Coccini,Saissetiini and most of Pulvinariini.Molecular data support the monophyletic group of Ceroplastinae,the other subfamilies are multiphyletic groups,and do not support the division of Filippiinae.According to the results of the study,it is suggested that Paralecaniini should be separated from Coccinae as a subfamily,and Megapulvinaria should be separated from Pulvinariini.