sentences:  A heptanucleotide that is located upstream of ORF (1897UUUUUUA) is found in both ESV and DXV.Together with phylogenetic analysis and the location differences of nucleotide and amino acids between CYV and ESV, it has been shown that CYV and ESV is one sister species to DXV.Although widely used in the laboratory, DXV has never been found as a natural infection of "Drosophila", and was originally identified in laboratory cell culture.