none Aphidius ervi; RIBOSOMES-; Gene identification; MOLECULAR-GENETICS; Ribosomal genes & site specific insertion elements; Identification, characterization & evolutionary significance; EVOLUTION-; Evolutionary relationships within Aphidius; Evidence from ribosomal genes & site specific insertion elements We performed a molecular analysis of the Aphidius ervi ribosomal gene structure. This insect belongs to a set of closely related Aphidiinae species of the genus Aphidius Nees, of relevant interest in biological control. We constructed A. ervi genomic libraries, cloned and characterized several rDNA repeating units and sequenced different regions of the rDNA cistrons. We have found that insertion sequences interrupt the A. ervi 28S rDNA genes: the sequences of the two 5' and 3' insertion-28S junctions show that the elements are present at the position where R1 elements have been found in various insect species. In addition, the insertion of the element produces a duplication of the 14 nt target region. The sequence analysis indicates that the A. ervi elements belong to the R1 retrotransposon family with a highly conserved reverse transcriptase domain.